This document summarizes a review article on exchange bias in ferromagnetic-antiferromagnetic systems. Exchange bias is a phenomenon where cooling a system through the Neel temperature of an antiferromagnet in the presence of a ferromagnet induces an anisotropy (exchange bias) in the ferromagnet. The key findings of the review are:
1. Exchange bias was first discovered in 1956 when studying cobalt particles embedded in cobalt oxide.
2. It has since been observed in small particles, inhomogeneous materials, ferromagnetic films on antiferromagnetic single crystals, and thin films.
3. Various theoretical models have been proposed to explain exchange bias based on interface coupling, anisotropies, and domain formation.
Superconductivity is characterized by zero electrical resistance and the Meissner effect, where magnetic fields are expelled. There are two types of superconductors - Type I, which have an abrupt transition to the normal state, and Type II, which have a more gradual transition. The BCS theory explains superconductivity as electrons pairing up into Cooper pairs at low temperatures, acting as bosons that condense into the same quantum state. Superconductors have applications in medical imaging, maglev trains, and power transmission due to their ability to carry high currents and create strong magnetic fields.
This document summarizes the history and principles of thermoelectricity. It discusses how in the 1820s, Thomas Seebeck discovered that connecting two different metals and maintaining a temperature difference between them produces an electric current, known as the Seebeck effect. Later, Jean Peltier found that applying a current to two metals produces heating or cooling at their junction. In 1851, Lord Kelvin discovered the Thomson effect regarding heat absorption or production based on current direction. The document then explains key concepts in thermoelectric materials like the Seebeck coefficient and figures of merit involving electrical conductivity and thermal conductivity. It also discusses applications of thermoelectric generators and coolers in various technologies.
Synthesis of Cobalt ferrite by Solid Reaction Methodsank_sanjay
Cobalt ferrite nano-crystalline powder was synthesized from the powder mixture of cobalt carbonate and iron oxide by mixed oxide ceramic method. The effects of temperature of calcination as well as molar ratio of CoCO3/Fe2O3 on the phase structure, morphology and magnetic properties of the products were studied using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM) techniques, respectively. The samples calcined at 800 and 900˚C consisted of cobalt ferrite, iron oxide and cobalt oxide. In the sample calcined at 1000˚C, the reaction was completed and single phase CoFe2O4 with a mean crystallite and particle sizes of 49 and 300 nm, respectively was obtained.
Spintronics is a NANO technology which deals with spin dependent properties of an electron instead of charge dependent properties.
One of the main advantage of spintronics over electronics is the magnets tend to stay magnetize which is sparking in the industry an interest for replacing computer’s semiconductor based components with magnetic ones, starting with the RAM.
With an all-magnetic RAM, it is now possible to have a computer that retains all the information put into it. Most importantly, there will be no ‘boot-up’ waiting period when power is turned on.
Another promising feature of spintronics is that it doesn’t require the use of unique and specialized semiconductor, there by allowing it to work with common metals like Cu, Al, Ag.
Spintronics will use less power than conventional electronics, because the energy needed to change spin is a minute fraction of what is needed to push charge around.
Conventional electronic devices ignore the spin property and rely strictly on the transport of the electrical charge of electrons.
Adding the spin degree of freedom provides new effects, new capabilities and new functionalities.
Hello, I am Subhajit Pramanick. I and my classmate, Anannya Sahaw, both presented this ppt in seminar of our Institute, Indian Institute of Technology, Kharagpur. The topic of this presentation is on exchange interaction and their consequences. It includes the basic of exchange interaction, the origin of it, classification of it and their discussions etc. We hope you will all enjoy by reading this presentation. Thank you.
superparamagnetism and its biological applicationsudhay roopavath
- Superparamagnetism occurs in small ferromagnetic or ferrimagnetic nanoparticles and implies single-domain particle sizes of a few nanometers. The magnetic moments of individual atoms combine to form a giant magnetic moment for the nanoparticle as a whole.
- Below the blocking temperature, nanoparticles behave superparamagnetically, with spontaneous fluctuations of the magnetization direction between θ=00 and θ=1800. Above the blocking temperature, nanoparticles behave paramagnetically.
- Superparamagnetism allows applications in areas like drug delivery, hyperthermia cancer treatment, magnetic resonance imaging, and gene therapy by exploiting the magnetic properties at the nanoscale.
This document discusses the history and properties of dielectric materials. It covers:
- The early history of dielectric materials from the 18th century experiments of Cunaeus and Musschenbroek to Maxwell's unified electromagnetic theory.
- The dynamic range over which dielectric spectroscopy can measure relaxation processes, from 10-5 to 10-12 seconds.
- The four main polarization mechanisms in dielectric materials: electronic, ionic, orientation, and space-charge polarization.
- Key dielectric concepts such as permittivity, dielectric constant, electric susceptibility, and the Clausius-Mossotti relation.
Thin film fabrication using thermal evaporationUdhayasuriyan V
Thermal evaporation is a physical vapor deposition technique where a material is heated in a vacuum until its surface atoms evaporate and are deposited as a thin film on a substrate. The document discusses the principles and working of thermal evaporation, including how the source material is resistively heated to evaporation, how substrates are cleaned, and the advantages of producing films in a high vacuum like reduced impurities. Thermal evaporation can deposit pure elements or compounds and is used to fabricate thin films for applications like semiconductors, solar cells, and optics.
Superconductivity is characterized by zero electrical resistance and the Meissner effect, where magnetic fields are expelled. There are two types of superconductors - Type I, which have an abrupt transition to the normal state, and Type II, which have a more gradual transition. The BCS theory explains superconductivity as electrons pairing up into Cooper pairs at low temperatures, acting as bosons that condense into the same quantum state. Superconductors have applications in medical imaging, maglev trains, and power transmission due to their ability to carry high currents and create strong magnetic fields.
This document summarizes the history and principles of thermoelectricity. It discusses how in the 1820s, Thomas Seebeck discovered that connecting two different metals and maintaining a temperature difference between them produces an electric current, known as the Seebeck effect. Later, Jean Peltier found that applying a current to two metals produces heating or cooling at their junction. In 1851, Lord Kelvin discovered the Thomson effect regarding heat absorption or production based on current direction. The document then explains key concepts in thermoelectric materials like the Seebeck coefficient and figures of merit involving electrical conductivity and thermal conductivity. It also discusses applications of thermoelectric generators and coolers in various technologies.
Synthesis of Cobalt ferrite by Solid Reaction Methodsank_sanjay
Cobalt ferrite nano-crystalline powder was synthesized from the powder mixture of cobalt carbonate and iron oxide by mixed oxide ceramic method. The effects of temperature of calcination as well as molar ratio of CoCO3/Fe2O3 on the phase structure, morphology and magnetic properties of the products were studied using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM) techniques, respectively. The samples calcined at 800 and 900˚C consisted of cobalt ferrite, iron oxide and cobalt oxide. In the sample calcined at 1000˚C, the reaction was completed and single phase CoFe2O4 with a mean crystallite and particle sizes of 49 and 300 nm, respectively was obtained.
Spintronics is a NANO technology which deals with spin dependent properties of an electron instead of charge dependent properties.
One of the main advantage of spintronics over electronics is the magnets tend to stay magnetize which is sparking in the industry an interest for replacing computer’s semiconductor based components with magnetic ones, starting with the RAM.
With an all-magnetic RAM, it is now possible to have a computer that retains all the information put into it. Most importantly, there will be no ‘boot-up’ waiting period when power is turned on.
Another promising feature of spintronics is that it doesn’t require the use of unique and specialized semiconductor, there by allowing it to work with common metals like Cu, Al, Ag.
Spintronics will use less power than conventional electronics, because the energy needed to change spin is a minute fraction of what is needed to push charge around.
Conventional electronic devices ignore the spin property and rely strictly on the transport of the electrical charge of electrons.
Adding the spin degree of freedom provides new effects, new capabilities and new functionalities.
Hello, I am Subhajit Pramanick. I and my classmate, Anannya Sahaw, both presented this ppt in seminar of our Institute, Indian Institute of Technology, Kharagpur. The topic of this presentation is on exchange interaction and their consequences. It includes the basic of exchange interaction, the origin of it, classification of it and their discussions etc. We hope you will all enjoy by reading this presentation. Thank you.
superparamagnetism and its biological applicationsudhay roopavath
- Superparamagnetism occurs in small ferromagnetic or ferrimagnetic nanoparticles and implies single-domain particle sizes of a few nanometers. The magnetic moments of individual atoms combine to form a giant magnetic moment for the nanoparticle as a whole.
- Below the blocking temperature, nanoparticles behave superparamagnetically, with spontaneous fluctuations of the magnetization direction between θ=00 and θ=1800. Above the blocking temperature, nanoparticles behave paramagnetically.
- Superparamagnetism allows applications in areas like drug delivery, hyperthermia cancer treatment, magnetic resonance imaging, and gene therapy by exploiting the magnetic properties at the nanoscale.
This document discusses the history and properties of dielectric materials. It covers:
- The early history of dielectric materials from the 18th century experiments of Cunaeus and Musschenbroek to Maxwell's unified electromagnetic theory.
- The dynamic range over which dielectric spectroscopy can measure relaxation processes, from 10-5 to 10-12 seconds.
- The four main polarization mechanisms in dielectric materials: electronic, ionic, orientation, and space-charge polarization.
- Key dielectric concepts such as permittivity, dielectric constant, electric susceptibility, and the Clausius-Mossotti relation.
Thin film fabrication using thermal evaporationUdhayasuriyan V
Thermal evaporation is a physical vapor deposition technique where a material is heated in a vacuum until its surface atoms evaporate and are deposited as a thin film on a substrate. The document discusses the principles and working of thermal evaporation, including how the source material is resistively heated to evaporation, how substrates are cleaned, and the advantages of producing films in a high vacuum like reduced impurities. Thermal evaporation can deposit pure elements or compounds and is used to fabricate thin films for applications like semiconductors, solar cells, and optics.
This document summarizes Konrad Dziatkowski's research on magnetic anisotropy in dilute magnetic semiconductors, specifically (III,Mn)V materials. It provides an overview of ferromagnetism in (Ga,Mn)As and challenges in growing high-quality films. It also describes experiments using ferromagnetic resonance to characterize magnetic anisotropy, including polar, azimuthal, and reorientation effects. Exchange biasing of (Ga,Mn)As with MnO is shown to induce unidirectional anisotropy. The goal is to understand magnetic interactions and anisotropy in these materials for applications in spin-based electronics.
Vivek Kumar Bhartiya presents on applications and the enigma of high temperature superconductors. He discusses how conventional theory like BCS theory explains low-temperature superconductors but does not predict room temperature superconductivity. The key enigma is understanding the mechanism behind high-temperature superconductors. His research aims to develop cheaper manufacturing techniques by doing theoretical work closely tied to experiments to help predict and achieve room temperature superconductivity.
High Entropy Alloy was discovered in 1996. Being a completely new topic, it is unknown to us in all aspects. It's excellent combination of all mechanical properties is representing a new frontier in Materials Engineering field of research.
This document discusses multiferoic materials, which exhibit more than one "primary ferroic order parameter" simultaneously. The four primary ferroic order parameters are ferromagnetism, ferroelectricity, ferroelasticity, and antiferromagnetism/ferrimagnetism. The document provides examples of natural and synthetic multiferoic materials and discusses their properties and applications. It also explains related effects like magnetoelectricity and piezoelectricity, describing how certain materials can generate an electric potential or mechanical strain in response to a magnetic or electric field.
This document summarizes a seminar on magnetic nanocomposites. It discusses how nanocomposites have particles mixed at the nanoscale, including magnetic nanocomposites containing ferromagnetic particles. The history of magnetic nanocomposites is reviewed, from early amorphous alloys to developments in the 1980s-1990s of alloys like FINEMET, NANOPERM, and HITPERM. Recent developments discussed include core-shell nanoparticles, colloidal crystals, mesoporous nanocomposites, and functional polymers. Applications mentioned are using magnetic fields to destroy tumor cells, transformers, and DC-DC power converters. Challenges remaining are controlled synthesis, understanding mechanisms, cost, toxicity
This document provides an introduction to 2D materials, including a brief history and overview of types. It discusses graphene, the earliest known 2D material, which consists of a single layer of carbon atoms arranged in a honeycomb structure. Graphene is nearly transparent, yet over 100 times stronger than steel. It has the highest thermal and electrical conductivity of any known material. The document also mentions other 2D materials like germanene, silicene, phosphorene, and transition metal dichalcogenides.
B.tech sem i engineering physics u iii chapter 2-superconductivityRai University
Superconductivity is a state where electrical resistance becomes zero below a critical temperature. The document discusses properties of superconductors like zero resistance, Meissner effect, magnetic flux quantization. It also explains BCS theory of superconductivity involving Cooper pairs and the energy gap. Applications of superconductors like MRI, maglev trains, Josephson junction devices like SQUIDs used for magnetic sensing are summarized.
Pieter Zeeman was a Dutch physicist who shared the 1902 Nobel Prize in Physics with Hendrik Lorentz for his discovery of the Zeeman effect in 1896. The Zeeman effect is the splitting of spectral lines into multiple components when in the presence of a magnetic field. Zeeman observed that each emission line from a light source split into several lines when under the influence of a magnetic field. This splitting, known as the Zeeman effect, demonstrated that atomic energy levels are affected by magnetic fields.
1) Ferrites are magnetic ceramic materials that have a wide variety of applications from microwave to radio frequencies due to their properties like high resistivity and permeability.
2) They are classified based on their crystal structure into spinel, garnet, ortho, and hexagonal ferrites. Soft ferrites are used in transformers while hard ferrites are used in permanent magnets.
3) Ferrites are synthesized using methods like solid state reaction, sol-gel, and precipitation. Their properties can be modified by controlling synthesis parameters.
4) Major applications of ferrites include transformers, inductors, antennas, recording heads, and magnetic shielding due to their advantages over metals.
Ferroelectric and piezoelectric materialsZaahir Salam
The document discusses piezoelectric and ferroelectric materials. It defines key terms like dielectric, polarization, and piezoelectric effect. It explains that piezoelectric materials can convert mechanical energy to electrical energy and vice versa. Ferroelectric materials are a special class of piezoelectric materials that exhibit spontaneous polarization without an electric field. Examples of naturally occurring and man-made piezoelectric crystals and ceramics are provided. Common applications of piezoelectric materials include sensors, actuators, generators, and memory devices.
Scanning tunneling microscopy (STM) allows investigation of surfaces down to the atomic scale by using quantum tunneling of electrons between a sharp tip and conductive sample. An STM works by scanning the tip across the sample in a constant-height or constant-current mode maintained by a feedback loop. The tunneling current depends exponentially on the tip-sample distance, enabling atomic resolution. STM is useful for imaging surfaces in materials science, physics, and biology and can provide topographic and spectroscopic information.
This document discusses superconductors and their properties. It begins by defining superconductivity as the phenomenon where certain materials conduct electricity without resistance when cooled below a critical temperature. It then discusses key properties of superconductors including zero electrical resistance, the effects of impurities and pressure, isotope effects, magnetic field effects, critical current density, and the Meissner effect. It categorizes superconductors as either type 1 or type 2 and provides examples of each. Finally, it outlines several applications of superconductors such as magnetic levitation trains, SQUID devices, and RF/microwave filters.
The document discusses 1st order and 2nd order phase transitions. 1st order transitions involve a release or absorption of latent heat and result in discontinuous changes in properties like entropy. 2nd order transitions do not involve latent heat and result in continuous changes in properties across the transition. The Landau theory of phase transitions provides a framework for describing transitions using a thermodynamic potential and order parameter. Gibbs free energy must be minimized at equilibrium, and 1st order transitions exhibit a discontinuity in the temperature dependence of entropy while 2nd order transitions do not.
Ferrites are iron-based magnetic compounds consisting of iron and one or more divalent metal ions such as magnesium, iron, or nickel. There are two types of ferrite crystal structures: regular spinel, where divalent ions occupy tetrahedral sites and trivalent iron ions occupy octahedral sites; and inverse spinel, where trivalent iron ions occupy both tetrahedral and half of the octahedral sites, with the remaining sites occupied by divalent ions. Ferrites are brittle ceramic materials with high resistivity and magnetic properties that make them useful for applications like transformer cores, ultrasound production, memory devices, and microwave components.
Ferromagnetic materials have three main characteristics:
1) They become spontaneously magnetized in the absence of an external magnetic field due to parallel alignment of magnetic moments.
2) They have a magnetic ordering temperature called the Curie temperature, above which they become paramagnetic.
3) They are used in many devices like transformers, electromagnets, and computer hard drives due to their magnetic properties.
The Wigner-Seitz cell is a Voronoi cell used to study crystalline solids in physics. It is defined as the region in space closer to a given lattice point than any other. The Wigner-Seitz cell of the reciprocal lattice is called the first Brillouin zone. In one dimension the Wigner-Seitz cell is an interval, in two dimensions it is typically a hexagon, and in three dimensions it takes the shape of the smallest polyhedron enclosing the lattice point and its nearest neighbors. Higher order Brillouin zones are identified by planes perpendicular to reciprocal lattice vectors, with the first zone being the smallest such region around the origin.
This document discusses magnetic properties of solids. It defines key terms like magnetization, magnetic susceptibility, paramagnetism and diamagnetism. Paramagnetism occurs in materials with partially filled electron subshells, allowing isolated atomic magnetic dipole moments to align with an external magnetic field. Diamagnetism is a weaker effect where an applied field induces orbital electron currents that create a magnetic field opposing the external field. The document outlines the classical and quantum mechanical origins of these magnetic behaviors.
This document discusses copper pairs and quantum tunneling in superconductivity. It first provides context on superconductivity, the Meissner effect, and BCS theory. It then explains that below the superconducting transition temperature, paired electrons called Cooper pairs form a condensate occupying a single quantum state, allowing them to flow without resistance. Cooper pairs consist of two electrons bound together at low temperatures according to BCS theory, despite their negative charges which would normally cause repulsion. The document also briefly mentions the concept of quantum tunneling in relation to superconductivity.
1. The document discusses the Fermi-Dirac distribution function, which describes the occupancy of energy levels by electrons in a solid.
2. The probability that an energy level E is filled by an electron is given by the Fermi-Dirac distribution function f(E) = 1/(1+e^(E-EF)/kT), where EF is the Fermi level energy.
3. The derivation of the Fermi-Dirac distribution function maximizes the logarithm of the multiplicity function, or number of configurations that electrons can occupy energy states, to find the occupancy probability that corresponds to thermal equilibrium.
Presentation of Licentiate in Physics Engineering of Francisco AlmeidaFrancisco Almeida
This seminar was presented to show the results of my research on magnetic thin films for my Licentiate diploma in Physics Engineering. This is a subset (although the biggest portion) of the analysis performed.
(note: the two last slides are not part of the actual presentation).
Magnon crystallization in kagomé antiferromagnetsRyutaro Okuma
This document summarizes research on magnon crystallization in kagomé antiferromagnets. Key points include:
1) Observation of a series of magnetization plateaus up to 160 T in CdK and a 1/3 magnetization plateau over 150 T in herbertsmithite.
2) Theoretical calculation showing hexagonal magnon localization and crystallization phases with different magnetization values as the field is increased.
3) Experimental studies of the S=1/2 kagomé magnets volborthite, herbertsmithite, and Cd-kapellasite using ultra-high magnetic fields up to 200 T to observe magnon crystallization phenomena.
This document summarizes Konrad Dziatkowski's research on magnetic anisotropy in dilute magnetic semiconductors, specifically (III,Mn)V materials. It provides an overview of ferromagnetism in (Ga,Mn)As and challenges in growing high-quality films. It also describes experiments using ferromagnetic resonance to characterize magnetic anisotropy, including polar, azimuthal, and reorientation effects. Exchange biasing of (Ga,Mn)As with MnO is shown to induce unidirectional anisotropy. The goal is to understand magnetic interactions and anisotropy in these materials for applications in spin-based electronics.
Vivek Kumar Bhartiya presents on applications and the enigma of high temperature superconductors. He discusses how conventional theory like BCS theory explains low-temperature superconductors but does not predict room temperature superconductivity. The key enigma is understanding the mechanism behind high-temperature superconductors. His research aims to develop cheaper manufacturing techniques by doing theoretical work closely tied to experiments to help predict and achieve room temperature superconductivity.
High Entropy Alloy was discovered in 1996. Being a completely new topic, it is unknown to us in all aspects. It's excellent combination of all mechanical properties is representing a new frontier in Materials Engineering field of research.
This document discusses multiferoic materials, which exhibit more than one "primary ferroic order parameter" simultaneously. The four primary ferroic order parameters are ferromagnetism, ferroelectricity, ferroelasticity, and antiferromagnetism/ferrimagnetism. The document provides examples of natural and synthetic multiferoic materials and discusses their properties and applications. It also explains related effects like magnetoelectricity and piezoelectricity, describing how certain materials can generate an electric potential or mechanical strain in response to a magnetic or electric field.
This document summarizes a seminar on magnetic nanocomposites. It discusses how nanocomposites have particles mixed at the nanoscale, including magnetic nanocomposites containing ferromagnetic particles. The history of magnetic nanocomposites is reviewed, from early amorphous alloys to developments in the 1980s-1990s of alloys like FINEMET, NANOPERM, and HITPERM. Recent developments discussed include core-shell nanoparticles, colloidal crystals, mesoporous nanocomposites, and functional polymers. Applications mentioned are using magnetic fields to destroy tumor cells, transformers, and DC-DC power converters. Challenges remaining are controlled synthesis, understanding mechanisms, cost, toxicity
This document provides an introduction to 2D materials, including a brief history and overview of types. It discusses graphene, the earliest known 2D material, which consists of a single layer of carbon atoms arranged in a honeycomb structure. Graphene is nearly transparent, yet over 100 times stronger than steel. It has the highest thermal and electrical conductivity of any known material. The document also mentions other 2D materials like germanene, silicene, phosphorene, and transition metal dichalcogenides.
B.tech sem i engineering physics u iii chapter 2-superconductivityRai University
Superconductivity is a state where electrical resistance becomes zero below a critical temperature. The document discusses properties of superconductors like zero resistance, Meissner effect, magnetic flux quantization. It also explains BCS theory of superconductivity involving Cooper pairs and the energy gap. Applications of superconductors like MRI, maglev trains, Josephson junction devices like SQUIDs used for magnetic sensing are summarized.
Pieter Zeeman was a Dutch physicist who shared the 1902 Nobel Prize in Physics with Hendrik Lorentz for his discovery of the Zeeman effect in 1896. The Zeeman effect is the splitting of spectral lines into multiple components when in the presence of a magnetic field. Zeeman observed that each emission line from a light source split into several lines when under the influence of a magnetic field. This splitting, known as the Zeeman effect, demonstrated that atomic energy levels are affected by magnetic fields.
1) Ferrites are magnetic ceramic materials that have a wide variety of applications from microwave to radio frequencies due to their properties like high resistivity and permeability.
2) They are classified based on their crystal structure into spinel, garnet, ortho, and hexagonal ferrites. Soft ferrites are used in transformers while hard ferrites are used in permanent magnets.
3) Ferrites are synthesized using methods like solid state reaction, sol-gel, and precipitation. Their properties can be modified by controlling synthesis parameters.
4) Major applications of ferrites include transformers, inductors, antennas, recording heads, and magnetic shielding due to their advantages over metals.
Ferroelectric and piezoelectric materialsZaahir Salam
The document discusses piezoelectric and ferroelectric materials. It defines key terms like dielectric, polarization, and piezoelectric effect. It explains that piezoelectric materials can convert mechanical energy to electrical energy and vice versa. Ferroelectric materials are a special class of piezoelectric materials that exhibit spontaneous polarization without an electric field. Examples of naturally occurring and man-made piezoelectric crystals and ceramics are provided. Common applications of piezoelectric materials include sensors, actuators, generators, and memory devices.
Scanning tunneling microscopy (STM) allows investigation of surfaces down to the atomic scale by using quantum tunneling of electrons between a sharp tip and conductive sample. An STM works by scanning the tip across the sample in a constant-height or constant-current mode maintained by a feedback loop. The tunneling current depends exponentially on the tip-sample distance, enabling atomic resolution. STM is useful for imaging surfaces in materials science, physics, and biology and can provide topographic and spectroscopic information.
This document discusses superconductors and their properties. It begins by defining superconductivity as the phenomenon where certain materials conduct electricity without resistance when cooled below a critical temperature. It then discusses key properties of superconductors including zero electrical resistance, the effects of impurities and pressure, isotope effects, magnetic field effects, critical current density, and the Meissner effect. It categorizes superconductors as either type 1 or type 2 and provides examples of each. Finally, it outlines several applications of superconductors such as magnetic levitation trains, SQUID devices, and RF/microwave filters.
The document discusses 1st order and 2nd order phase transitions. 1st order transitions involve a release or absorption of latent heat and result in discontinuous changes in properties like entropy. 2nd order transitions do not involve latent heat and result in continuous changes in properties across the transition. The Landau theory of phase transitions provides a framework for describing transitions using a thermodynamic potential and order parameter. Gibbs free energy must be minimized at equilibrium, and 1st order transitions exhibit a discontinuity in the temperature dependence of entropy while 2nd order transitions do not.
Ferrites are iron-based magnetic compounds consisting of iron and one or more divalent metal ions such as magnesium, iron, or nickel. There are two types of ferrite crystal structures: regular spinel, where divalent ions occupy tetrahedral sites and trivalent iron ions occupy octahedral sites; and inverse spinel, where trivalent iron ions occupy both tetrahedral and half of the octahedral sites, with the remaining sites occupied by divalent ions. Ferrites are brittle ceramic materials with high resistivity and magnetic properties that make them useful for applications like transformer cores, ultrasound production, memory devices, and microwave components.
Ferromagnetic materials have three main characteristics:
1) They become spontaneously magnetized in the absence of an external magnetic field due to parallel alignment of magnetic moments.
2) They have a magnetic ordering temperature called the Curie temperature, above which they become paramagnetic.
3) They are used in many devices like transformers, electromagnets, and computer hard drives due to their magnetic properties.
The Wigner-Seitz cell is a Voronoi cell used to study crystalline solids in physics. It is defined as the region in space closer to a given lattice point than any other. The Wigner-Seitz cell of the reciprocal lattice is called the first Brillouin zone. In one dimension the Wigner-Seitz cell is an interval, in two dimensions it is typically a hexagon, and in three dimensions it takes the shape of the smallest polyhedron enclosing the lattice point and its nearest neighbors. Higher order Brillouin zones are identified by planes perpendicular to reciprocal lattice vectors, with the first zone being the smallest such region around the origin.
This document discusses magnetic properties of solids. It defines key terms like magnetization, magnetic susceptibility, paramagnetism and diamagnetism. Paramagnetism occurs in materials with partially filled electron subshells, allowing isolated atomic magnetic dipole moments to align with an external magnetic field. Diamagnetism is a weaker effect where an applied field induces orbital electron currents that create a magnetic field opposing the external field. The document outlines the classical and quantum mechanical origins of these magnetic behaviors.
This document discusses copper pairs and quantum tunneling in superconductivity. It first provides context on superconductivity, the Meissner effect, and BCS theory. It then explains that below the superconducting transition temperature, paired electrons called Cooper pairs form a condensate occupying a single quantum state, allowing them to flow without resistance. Cooper pairs consist of two electrons bound together at low temperatures according to BCS theory, despite their negative charges which would normally cause repulsion. The document also briefly mentions the concept of quantum tunneling in relation to superconductivity.
1. The document discusses the Fermi-Dirac distribution function, which describes the occupancy of energy levels by electrons in a solid.
2. The probability that an energy level E is filled by an electron is given by the Fermi-Dirac distribution function f(E) = 1/(1+e^(E-EF)/kT), where EF is the Fermi level energy.
3. The derivation of the Fermi-Dirac distribution function maximizes the logarithm of the multiplicity function, or number of configurations that electrons can occupy energy states, to find the occupancy probability that corresponds to thermal equilibrium.
Presentation of Licentiate in Physics Engineering of Francisco AlmeidaFrancisco Almeida
This seminar was presented to show the results of my research on magnetic thin films for my Licentiate diploma in Physics Engineering. This is a subset (although the biggest portion) of the analysis performed.
(note: the two last slides are not part of the actual presentation).
Magnon crystallization in kagomé antiferromagnetsRyutaro Okuma
This document summarizes research on magnon crystallization in kagomé antiferromagnets. Key points include:
1) Observation of a series of magnetization plateaus up to 160 T in CdK and a 1/3 magnetization plateau over 150 T in herbertsmithite.
2) Theoretical calculation showing hexagonal magnon localization and crystallization phases with different magnetization values as the field is increased.
3) Experimental studies of the S=1/2 kagomé magnets volborthite, herbertsmithite, and Cd-kapellasite using ultra-high magnetic fields up to 200 T to observe magnon crystallization phenomena.
Polymorphic Nanocrystalline Metal Oxidesshantanusood
This document discusses polymorphic nanocrystalline metal oxides and their thermodynamics and applications. It explains that nanocrystalline metal oxides exhibit polymorphic phase transitions at lower temperatures and pressures than their bulk counterparts due to effects of increased internal pressure and surface energy at the nanoscale. A thermodynamic model is presented to explain how surface area to volume ratio and internal pressure effects can lower the activation barrier for phase transitions. Examples of different polymorphic phases exhibited by various metal oxides at the bulk and nanoscale are provided. Applications of polymorphic nanocrystalline metal oxides in gas sensing, catalysis, solid oxide fuel cells, and electrochemical energy storage are discussed.
Magnetic materials form magnetic domains to minimize their magnetostatic energy. Domain walls separate domains with different magnetization orientations. Bloch walls have spins rotating continuously across the wall, while Neel walls have spins rotating in the plane of the wall. The equilibrium domain size and wall thickness are determined by a balance of exchange, anisotropy, magnetostatic, and wall energies. Various techniques like SEMPA, MFM, and magneto-optical imaging are used to observe domain structures with high resolution.
Report on Giant Magnetoresistance(GMR) & Spintronicsaltafmahmood1
This document provides background information on giant magnetoresistance (GMR). It discusses how GMR was discovered in 1988 by two research groups who found that thin film structures made of alternating ferromagnetic and nonmagnetic layers exhibited a significant decrease in electrical resistance of up to 80% in the presence of an external magnetic field. This effect occurs because the magnetization of adjacent ferromagnetic layers changes from antiparallel to parallel when a field is applied, lowering magnetic scattering and resistance. The discovery of GMR opened up new possibilities for data storage technologies and magnetic sensors.
This document summarizes research on designing annular ring frequency selective surfaces (FSS) using different dielectric substrate materials. The research aims to achieve dual-band frequency response with controllable shift in resonance frequencies. FSS designs with annular ring elements are simulated using substrates like Teflon, Mica and FR4. Simulation results show dual transmission bands in C-band and X-band, with the frequencies shifting based on the dielectric constant of the material. Teflon provides the highest resonance frequencies while Mica and FR4 shift the frequencies down as their dielectric constants increase. The study demonstrates annular ring FSS can produce dual-band response with substrate material choice enabling predictable frequency shifts.
This document summarizes recent developments in magnetic separation techniques. It discusses how magnetic separation works by exploiting differences in magnetic susceptibility between materials. Advances in permanent magnets and electromagnets have allowed generation of stronger magnetic fields and gradients, enabling separation of finer and less magnetic particles. The key developments include more powerful rare-earth permanent magnets generating over 1.9T fields, resistive electromagnets producing over 2T, and use of ferromagnetic matrices increasing field gradients over 50,000T/m. These innovations have expanded the range of materials that can be separated magnetically from coarse to colloidal sizes.
Decay of helical and non-helical magnetic links and knotsSimon Candelaresi
The decay characteristics of magnetic fields of the form of interlinked structures and knots depends heavily on the magnetic helicity. However there are cases where other topological invariants may play are role.
www.nordita.org/~iomsn/
This document discusses the recycling of magnetic flux in the quiet Sun's corona. It presents a study that uses magnetogram observations to track photospheric magnetic flux fragments over time and models their evolution using a potential field approximation. The main findings are:
1) The quiet Sun's coronal flux is generally recycled on much shorter timescales, around 3 hours, than the corresponding recycling timescale of photospheric flux, which is around 8-19 hours.
2) When also considering emergence and cancellation of photospheric flux, the net replacement time of coronal flux is estimated to be only 1.4 hours.
3) The amount of magnetic reconnection driven by the motions and interactions of photospheric
This document summarizes research on amphiphiles and Langmuir monolayers. It discusses how amphiphiles are composed of a hydrophilic head and hydrophobic tail. When spread on water, amphiphiles form Langmuir monolayers where the heads interact with water and tails with air. Pressure-area isotherms of these monolayers show phase transitions as pressure increases. Adding metal ions to the water subphase can induce superlattice formation underneath the monolayer. Studies using x-ray diffraction and other techniques characterized the structures of various Langmuir monolayers and how they change with conditions like subphase pH and metal ion type.
Enhanced Exchange Pinning Field For Fe Mn Spin Valvesguestc57e7ed
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2. Exchange bias [Journal of Magnetism and Magnetic Materials, 192, (1999) 203-232]
J. Nogues, Ivan K. Schuller
3. When materials with ferromagnetic (FM)-antiferromagnetic (AFM) interfaces are cooled
through the Neel temperature of the AFM (with the Curie temperature of the FM larger than
Neel temp.) an anisotropy (exchange bias) is induced in the FM.
Discovered in 1956 by MeikleJohn and Bean
when studying Co particles embedded in
their native antiferromagnetic oxide (CoO)
1. Material Used : Co as a Core and CoO as a Shell
2. Method : Electrodeposition
3. Particle Size : ~200Å
4. The material is cooled from the paramagnetic state of the
oxide to the antiferromagnetic state in a saturating
magnetic field. Since the Neel temperature of cobaltous
oxide is 293K, the material was cooled from 300K to 77K
in a magnetic field.
Ref : W.H. Meiklejohn, C.P. Bean, Phys. Rev. 102 (1956) 1413.
Definition:
4. Other Systems in which this anisotropy discovered
1. Small particles
2. Inhomogeneous materials
3. FM films on AFM single crystal
4. Thin films
Phenomenology:
Ref : J. Nogues, T.J. Moran, D. Lederman, I.K. Schuller, K.V. Rao, Phys. Rev. B
• Static magnetic field from a temperature above TN but below TC to temp.
T<TN
• After T<TN Field cooling procedure shifts the hysteresis loop in opposite
direction
• Absolute value of coercive field for decreasing and increasing field is
different
• This loop shift is normally called as Exchange Bias, HE
• Coercivity increased after field cool procedure
• Both effect disappear at (or) close to Neel Temp.
7. Materials:
1. Small Particles:
• Parameter exhibited by most fine particles:
1. Non-vanishing rotational hysteresis
2. Increase of coercivity below TN.
• These properties related to surface layer of the particle which due to the
changes in the atomic coordination form a layer of disordered spins.
• Particles behaves as a two magnetic system.
Disadvantage:
• Difficult to compare results quantitatively
• Non ideal for Exchange Bias:
1. Distribution of particle shapes and size is always present
2. Difficulty to identify the nature of interface.
3. Stoichiometry
4. Crystallinity
Ref : W.H. Meiklejohn, C.P. Bean, Phys. Rev. 102 (1956) 1413.
8. Ref : Review: J.S. Kouvel, J. Phys. Chem. Sol. 24 (1963) 795.
2. Inhomogeneous materials: (materials without well defined interfaces)
Spin glass and some ferrimagnets
Example:
1. Cu1-xMnx
2. Ag1-xMnx
3. Ni1-xMnx
(Au1-xFex)
Exchange bias is an intrinsic property of material rather than a sample preparation artifact.
(Which has been observed)
Polycrystalline
Single crystal
Thin film form
Amorphous materials
• Fe1-xZrx
• Ni1-xMnx
• P16B6Al3
Other example of inhomogeneous materials: (multiple FM-AFM interface)
• Co sputtered in low O2 pressure atm.
• Co-sputtered CoCr or NiO with NiFe2O3 precipitates.
9. 3. Coated antiferromagnetic single crystals:
1. Role of spin configuration at the interface (by selecting different crystallographic directions)
2. Role of the roughness (by controllably damaging the AFM surface before depositing the FM)
(two important aspect of Exchange bias)
Exchange bias exhibited ay all three systems are substantially smaller than the one obtained in small particles
or thin films.
1. AFM surface is contaminated before transferring the single crystal to the deposition chamber.
2. Very little dependence of the Exchange bias on the spin configuration of the AFM at the interface.
(Why?)
Compensated AFM surface Uncompensated AFM surface
Ref: J. Nogue, I.K. Schuller / Journal of Magnetism and Magnetic Materials 192 (1999) 203-232
10. 4. Thin films:
• Interface can be quite effectively controlled and characterized
• Most of the device application are in thin film form
Some interesting phenomenon:
• AFM thickness
• Interface disorder or Orientation dependence
• The magnitude of Exchange bias is described in terms of an
interface energy per unit area
∆𝑬 = 𝑴 𝑭𝑴 𝒕 𝑭𝑴 𝑯 𝑬
1. Oxide AFM
2. Metallic AFM
3. Ferrimagnets
4. Other AFM
(Types)
Saturation magnetisation
Thickness of Ferro-magnet
This kind of samples are difficult to compare
Oxide layer can measured accurately
Film oxidized through grain boundaries
Increasing the interface surface
Antiferromagnetic oxides have been
sputtered directly from the oxide or in a
reactive oxygen atmosphere.
Surprisingly, well oriented AFM oxides can exhibit smaller exchange bias than oxidized metallic layers or polycrystalline
AFM layers, probably due to oxidation through grain boundaries, increasing the effective interface area or other magnetic
or microstructural factors.
Problems
Solution
Ref: J. Nogue & I.K. Schuller / Journal of Magnetism and Magnetic Materials 192 (1999) 203-232
13. Applications:
• Permanent magnet materials
• High density Recording media
• Perpendicular Recording media
• Magnetic Recording Media
• Domain Stabilizer
(In recording media heads based on
anisotropic magnetoresistance. An AFM layer
is deposited on the edge of the FM layer, to
avoid closure domains and thus reduce the
Barkhausen noise of the devices.)
Recently Exchange Bias became part of new class of ‘spin-valve’ devices, based on GMR.
This type of device consists of two FM layers separated be a non magnetic layer.
FM
FM
AFM
Free
Pinned
Ref: B. Dieny, V.S. Speriosu, S.S.P. Parkin, B.A. Gurney, D.R.Wilhoit, D. Mauri, Phys. Rev. B 43 (1991) 1297.
Low to high resistance occurs at rather low fields.
GMR in Exchange Bias
Read heads
Magnetic sensors
Magnetoresistive memories
15. 𝑬 = −𝑯𝑴 𝑭𝑴 𝒕 𝑭𝑴 𝐜𝐨𝐬 𝜽 − 𝜷 + 𝑲 𝑭𝑴 𝒕 𝑭𝑴 𝒔𝒊𝒏 𝟐 𝜷 + 𝑲 𝑨𝑭𝑴 𝒕 𝑨𝑭𝑴 𝒔𝒊𝒏 𝟐 𝜶 − 𝑱 𝑰𝑵𝑻 𝐜𝐨𝐬(𝜷 − 𝜶)
Effect of applied field on FM layer Effect of FM anisotropyEffect of AFM anisotropy Effect of interface coupling
Condition: 1
𝐊 𝐅𝐌 𝐭 𝐅𝐌 ≪ 𝐊 𝐀𝐅𝐌 𝐭 𝐀𝐅𝐌
𝑬 = −𝑯𝑴 𝑭𝑴 𝒕 𝑭𝑴 𝐜𝐨𝐬 𝜽 − 𝜷 + 𝑲 𝑨𝑭𝑴 𝒕 𝑨𝑭𝑴 𝒔𝒊𝒏 𝟐
𝜶 − 𝑱 𝑰𝑵𝑻 𝐜𝐨𝐬(𝜷 − 𝜶) 𝑯 𝑬 =
𝑱 𝑰𝑵𝑻
𝑴 𝑭𝑴 𝒕 𝑭𝑴
𝐊 𝐀𝐅𝐌 𝐭 𝐀𝐅𝐌 ≫ 𝐉𝐈𝐍𝐓
𝐊 𝐀𝐅𝐌 𝐭 𝐀𝐅𝐌 ≪ 𝐉𝐈𝐍𝐓
System is minimized by keeping α small independently of β.
It is energetically more favourable to keep (β-α) small, i.e. AFM-FM spins rotates together
The AFM spins follow the motion of FM layer, thus no loop shift should be observed, only an increase in coercivity.
Condition: 2
16. If JINT is taken to be similar to the ferromagnetic exchange, HE is predicted to be several orders of magnitude
larger than the experimental result.
1. Formation of domains in the AFM or FM layer
2. Field effect on AFM layer
3. Grain size distribution
4. Induced thermoremanent magnetization in the AFM layer
5. Non-collinearity of AFM-FM spins
6. Random anisotropy in the AFM layer or uncompensated surface spins
Important parameter in Exchange Bias which
are not considered in basic formula.
Ref :
• R. Jungblut, R. Coehoorn, M.T. Johnson, J. aan deStegge, A. Reinders, J. Appl. Phys. 75 (1994) 6659.
• K. Takano, R.H. Kodama, A.E. Berkowitz, W. Cao, G.Thomas, Phys. Rev. Lett. 79 (1997) 1130.
• A.A. Glazer, A.P. Potapov, R.I. Tagirov, Y.S. Shur, Sov. Phys. Sol. State 8 (1967) 2413.
• E. Fulcomer, S.H. Charp, J. Appl. Phys. 43 (1972) 4190.
17. • In a recent model in which quantum mechanical Hamiltonian is solved for spin compensated AFM surfaces,
HE arises from spin waves transmitted across the interface.
• This model assumes unidimensional and collinear spins.
Another model:
AFM Domains Perpendicular coupling
• The formation of AFM domains perpendicular to the
interface plane due to the random field created by
roughness and it is contribution of energy difference
between the different random domains which produce
Exchange Bias.
• Other model claims that formation of AFM domains
parallel to the interface when the FM layer rotates can
also cause Exchange Bias.
Ref:
1. A.P. Malozemoff, Phys. Rev. B 35 (1987) 3679.
2. A.P. Malozemoff, J. Appl. Phys. 63 (1988) 3874.
3. D. Mauri, H.C. Siegmann, P.S. Bagus, E. Kay, J. Appl.Phys. 62 (1987) 3047.
4. N.C. Koon, Phys. Rev. Lett. 78 (1997) 4865.
• For a compensated surface the interfacial energy
is minimized for perpendicular coupling between
the FM and AFM layers.
Ref: N.C. Koon, Phys. Rev. Lett. 78 (1997) 4865.
Ref: H. Suhl, I.K. Schuller, Phys. Rev. B 58 (1998) 158.
18. Unsolved Issues:
1. Thickness dependence
FM Thickness AFM Thickness
𝑯 𝑬 ∝
𝟏
𝒕 𝑭𝑴
Ref: Review: F.S. Luborsky, Electro-Technology (Sept. 1962)107.
• As the AFM thickness is reduced HE decreases abruptly
and finally for thin enough AFM layers HE becomes zero.
• Exchange bias requires the condition:
• As tAFM is reduced condition is violated.
𝐊 𝐀𝐅𝐌 𝐭 𝐀𝐅𝐌 ≫ 𝐉𝐈𝐍𝐓
2. AFM orientation
Compensated – Uncompensated:
1. Net spin averaged over a microscopic length scale is zero Zero magnetization.
2. If the spin arrangement is such that the surface magnetization is non zero the surface is uncompensated.
3. For compensated surfaces the spin pinning of FM layers cancel giving rise to a net zero HE.
4. A compensated surface remains compensated in the presence of unit cell random roughness however
more complicated roughness could result in uncompensated surfaces.
5. All compensated surfaces exhibit Exchange Bias.
Ref: T.J. Moran, J.M. Gallego, I.K. Schuller, J. Appl. Phys. 78(1995) 1887., A.E. Berkowitz, J.H. Greiner, J. Appl. Phys. 36 (1965)3330.
19. Out of the plane spins:
An intuitive explanation for this effect comes from the FM-AFM spin-spin interaction strength,
𝑺∗
𝑨𝑭𝑴. 𝑺∗
𝑭𝑴 = 𝑺 𝑨𝑭𝑴 𝑺 𝑭𝑴 𝒄𝒐𝒔𝜶
If FM spins lay in the interface plane due to shape anisotropy α is the angle between the AFM spins and the interface
plane. Therefore for in plane AFM spins:
α = 0° cosα = 1 HE maximum
and for out of plane spins:
α = 90° cosα = 0 HE = 0
Another possible explanation assumes that the dominant factor in HE is AFM domain formation.
𝑯 𝑬 ∝ 𝑲 𝑨𝑭𝑴 𝑨 𝑨𝑭𝑴
Thus in case of out of plane AFM spins, the effective AFM in plane anisotropy Keff and stiffness Aeff would play a
mojor role.
Due to angle of AFM spins, effective anisotropy and stiffness at the interface plane should scale with cosα.
𝑯 𝑬 ∝ 𝑲 𝑬𝒇𝒇 𝑨 𝑬𝒇𝒇 = 𝑲 𝑨𝑭𝑴 𝑨 𝑨𝑭𝑴 𝒄𝒐𝒔𝜶
Ref: D. Mauri, H.C. Siegmann, P.S. Bagus, E. Kay, J. Appl.Phys. 62 (1987) 3047, A.P. Malozemoff, Phys. Rev. B 35 (1987) 3679.
20. 3. Interface disorder
Roughness
Magnitude of HE decreases with
increasing roughness.
This behaviour appears to be independent
of the interface spin structure i.e.
compensated, uncompensated or out of
plane.
Magnitude of HE increasing with
increasing roughness has been observed
for FM coated AFM single crystal
indicating that microstructure may
play an important role.
HE for samples with polycrystalline AFM
layers appear to be less sensitive to
roughness.
Ref:
K. Takano, R.H. Kodama, A.E. Berkowitz, W. Cao, G.
Thomas, Phys. Rev. Lett. 79 (1997) 1130.
A.P. Malozemoff, J. Appl. Phys. 63 (1988) 3874.
Crystallinity
The crystallinity may be determined using
XRD from the FWHM of rocking curve
however some information can be
obtained from θ-2θ scans and TEM.
If AFM is textured in single orientation HE
increases with increasing texture.
If the sample has a wider rocking curve
the different grains will have a wider
range of coupling FM-AFM angles thus
reducing HE
Ref:
R.P. Michel, A. Chaiken, Y.K. Kim, L.E. Johnson,
IEEE Trans. Magn. 32 (1996) 4651.
C.M. Park, K.I. Min, K.H. Shin, J. Appl. Phys. 79
(1996) 6228.
Grain Size
Role of grain size in Exchange bias
remains unclear.
AFM grain size are expected to be
similar to thickness effects i.e. HE
and TB should decrease with reduced
AFM grain size.
The role of grain size is related not
only to the change in its size but
also to the degree of the texture,
the spin structure and AFM
anisotropy.
Ref:
C.H. Lai, T.C. Anthony, R. Iwamura, R.L.
White, IEEE Trans. Magn. 32 (1996) 3419.
C.H. Lai, H. Matsuyama, R.L. White, T.C.
Anthony, IEEE Trans. Magn. 31 (1995) 2609.
21. Anisotropy
• The Exchange bias should be larger for larger AFM anisotropy.
• The main difficulty in analysing these results rises from the fact that they involve mixtures or dilution of AFM materials,
therefore the absolute value of anisotropy is usually unknown.
• It is important to consider that different materials have different blocking temperature thus HE should be considered at the same
reduced temperature T/TB.
• The anisotropy of AFM materials and HE depend on microstructure of AFM layer, Exact quantitative analysis is
difficult.
Ref: M.J. Carey, A.E. Berkowitz, Appl. Phys. Lett. 60 (1992) 3060, C.H. Lai, W.E. Bailey, R.L. White, T.C. Anthony, J. Appl. Phys. 81 (1997) 4990.
Blocking Temperature
• Exchange bias vanishes above a temperature often denoted as blocking temperature, TB.
• The origin of this effect is seems to be related at least in part to the grain size and thickness of the AFM layer, through finite
size effects.
• Other size effect are caused by the fact that the anisotropy of the AFM depends on its dimension and that the condition
• Other factors influencing TB include stoichiometry or presence of multiple phases of certain thin film systems.
Ref: Y. Tsuchiya, K. Kosuge, S. Yamaguchi, N. Nakayama,Mater. Trans. JIM 38 (1997) 91. , M. Tsunoda, Y. Tsuchiya, M. Konoto, M. Takahashi, J. Magn. Magn.
Mater. 171 (1997) 29.
𝐊 𝐀𝐅𝐌 𝐭 𝐀𝐅𝐌 ≫ 𝐉𝐈𝐍𝐓
22. Training Effect:
• It is well known that in many Exchange biases film systems, HE depends on the number of measurements, a property often
called a Training Effect.
• If several consecutive hysteresis loops are measured, the shift of these decreases. This phenomenon has also been observed
using others techniques such as torque measurement.
• It is important to note that this phenomenon is more important in polycrystalline AFM, and very small or non-existent
in system based on single crystal.
• This effect is seems to be related to partial reorientation of the AFM domains with each FM magnetization reversal.
Ref: D. Paccard, C. Schlenker, O. Massanet, R. Montmory, A.Yelon, Phys. Stat. Sol. 16 (1966) 301., T.J. Moran, J.M. Gallego, I.K. Schuller, J. Appl. Phys. 78 (1995)
1887
Coercivity:
• The coercivity usually increases below TB, which is probably linked to the anisotropy of the AFM layer.
• In the case of an AFM with small anisotropy, when the FM rotates it ‘drags’ the AFM spins irreversibly, hence increasing
the FM coercivity.
• For a large AFM anisotropy the FM decouples because it can not drag AFM spins, consequently the coercivity is reduced.
Ref: M.J. Carey, A.E. Berkowitz, Appl. Phys. Lett. 60 (1992)3060., C.H. Lai, H. Matsuyama, R.L. White, T.C. Anthony, G.G. Bush, J. Appl. Phys. 79 (1996) 6389.
23. Perpendicular Coupling:
• Several system exhibit a perpendicular coupling at the interface between the FM and AFM spins.
• Perpendicular coupling has been observed in compensated and uncompensated AFM surfaces.
• This effect has been theoretically predicted for AFM-FM systems when the FM has a low anisotropy.
• Some degree of non collinear coupling has been observed in others systems by torque magnetometry and domain observation.
• The lowest energy configuration for a compensated surface is with the FM orientated perpendicular to the two AFM
sublattices.
• This reasoning can be extended to uncompensated surfaces if due to the fluctuations, e.g. roughness, domain formation, etc., the
AFM spins arrange themselves antiparallel at the interface.
Ref: T.J. Moran, I.K. Schuller, J. Appl. Phys. 79 (1996)5109., T.J. Moran, J. Nogue«s, D. Lederman, I.K. Schuller, Appl. Phys. Lett. 72 (1998) 617.,
C. Schlenker, Phys. Stat. Sol. 28 (1968) 507.0