Magnetics.ppt [compatibility mode]

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Introduction to advanced ceramics

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Magnetics.ppt [compatibility mode]

  1. 1. Magnetic Ceramics Marzia Hoque Tania
  2. 2. Introduction  Magnetism is the force of attraction or repulsion of a magnetic material due to the arrangement of its atoms, particularly its electrons.  All magnetic phenomena result from forces between electric charges in motion.  Magnetism is the force of attraction or repulsion of a magnetic material due to the arrangement of its atoms, particularly its electrons.  All magnetic phenomena result from forces between electric charges in motion.
  3. 3. Demonstration of the magnetic moment associated with (a) an orbiting electron and (b) a spinning electron.
  4. 4. Classifications  There are various types of magnetic material classified by their magnetic susceptibilities: diamagnetic paramagnetic and ferromagnetic/ferrimagnetic.  There are various types of magnetic material classified by their magnetic susceptibilities: diamagnetic paramagnetic and ferromagnetic/ferrimagnetic.
  5. 5. Weak Magnetism Diamagnetism  Induced magnetic dipoles directed reverse to the external magnetic field.  Requirements: atoms with completely filled orbitals  Magnetic moment: no magnetic moment without applied field compensation of spin moments  Permeability / susceptibility: μr< 1 , χm < 0 (weak effect)  Materials: inert gases, ionic crystals, semiconductors, Cu, Au, Ag Diamagnetism  Induced magnetic dipoles directed reverse to the external magnetic field.  Requirements: atoms with completely filled orbitals  Magnetic moment: no magnetic moment without applied field compensation of spin moments  Permeability / susceptibility: μr< 1 , χm < 0 (weak effect)  Materials: inert gases, ionic crystals, semiconductors, Cu, Au, Ag
  6. 6. Weak Magnetism: Diamagnetism  direction of magnetic moments (H = 0):  impact on lines of flux in a homogeneous magnetic field:  direction of magnetic moments (H = 0):  impact on lines of flux in a homogeneous magnetic field:
  7. 7. Weak Magnetism: Diamagnetism
  8. 8. Weak Magnetism: Diamagnetism
  9. 9. Weak Magnetism: Diamagnetism
  10. 10. Weak Magnetism Paramagnetism  Alignment of permanent magnetic dipoles in the direction of the external magnetic field.  requirements: atoms with partially filled orbitals  magnetic moment: permanent magnetic moment <<, without external field disordering of magnetic moments  permeability / susceptibility: μr > 1 , χm > 0 (weak effect)  materials: Alkali- and transition metals, rare earth metals O2, Al, Sn, Pt Paramagnetism  Alignment of permanent magnetic dipoles in the direction of the external magnetic field.  requirements: atoms with partially filled orbitals  magnetic moment: permanent magnetic moment <<, without external field disordering of magnetic moments  permeability / susceptibility: μr > 1 , χm > 0 (weak effect)  materials: Alkali- and transition metals, rare earth metals O2, Al, Sn, Pt
  11. 11. Weak Magnetism: Paramagnetism  direction of magnetic moments (H = 0):  impact on lines of flux in a homogeneous magnetic field:  direction of magnetic moments (H = 0):  impact on lines of flux in a homogeneous magnetic field:
  12. 12. Weak Magnetism: Paramagnetism
  13. 13. Weak Magnetism: Paramagnetism
  14. 14. Weak Magnetism: Paramagnetism
  15. 15. Strong Magnetism Ferromagnetism  Spontaneous alignment of all permanent magnetic dipoles within a domain in the crystal lattice (only metals).  requirements: atoms with partially filled orbitals  magnetic moment: large magnetic moment, spontaneous magnetization formation of domains  permeability: μr>> 1 , χm > 0 (strongest type of magnetism)  materials: Fe, Co, Ni, alloys Ferromagnetism  Spontaneous alignment of all permanent magnetic dipoles within a domain in the crystal lattice (only metals).  requirements: atoms with partially filled orbitals  magnetic moment: large magnetic moment, spontaneous magnetization formation of domains  permeability: μr>> 1 , χm > 0 (strongest type of magnetism)  materials: Fe, Co, Ni, alloys
  16. 16. Strong Magnetism: Ferromagnetism  direction of magnetic moments (H = 0):  impact on lines of flux in a homogeneous magnetic field:  direction of magnetic moments (H = 0):  impact on lines of flux in a homogeneous magnetic field:
  17. 17. Strong Magnetism: Ferromagnetism  Ferromagnetic material is one that undergoes a phase transition from a high-temperature phase that does not have a macroscopic magnetic moment to a low- temperature phase that has a spontaneous magnetization even in the absence of an applied magnetic field.  The macroscopic magnetization is caused by the magnetic dipole moments of the atoms (which are aligned randomly in the high-temperature paramagnetic phase tending to line up in the same direction.  Ferromagnetic material is one that undergoes a phase transition from a high-temperature phase that does not have a macroscopic magnetic moment to a low- temperature phase that has a spontaneous magnetization even in the absence of an applied magnetic field.  The macroscopic magnetization is caused by the magnetic dipole moments of the atoms (which are aligned randomly in the high-temperature paramagnetic phase tending to line up in the same direction.
  18. 18. Strong Magnetism: Ferromagnetism  The spontaneous magnetization means that ferromagnetic materials tend to concentrate magnetic flux density (they have a large positive permeability), which leads to their widespread use in applications such as transformer cores, permanent magnets, and electromagnets, for which large magnetic fields are required.  The spontaneous magnetization means that ferromagnetic materials tend to concentrate magnetic flux density (they have a large positive permeability), which leads to their widespread use in applications such as transformer cores, permanent magnets, and electromagnets, for which large magnetic fields are required.
  19. 19. Strong Magnetism: Ferromagnetism  There are two phenomenological theories of ferromagnetism that have been successful in explaining many of the properties of ferromagnets: 1. Curie Weiss localized-moment theory 2. Stoner band theory of ferromagnetism
  20. 20. Weak Ferromagnetism: Antiferromagnetism Antiferromagnetism  Compensation of all magnetic dipoles due to an antiparallel alignment.  requirements: atoms with partially filled orbitals, atomic distance << magnetic moment: full compensation of the magnetization by antiparallel alignment  permeability: μr≈ 1 , χm ≈ 0 (weak magnetism)  materials: MnO, FeO, CoO, NiO and other metal-oxides Antiferromagnetism  Compensation of all magnetic dipoles due to an antiparallel alignment.  requirements: atoms with partially filled orbitals, atomic distance << magnetic moment: full compensation of the magnetization by antiparallel alignment  permeability: μr≈ 1 , χm ≈ 0 (weak magnetism)  materials: MnO, FeO, CoO, NiO and other metal-oxides
  21. 21. Weak Ferromagnetism: Antiferromagnetism  direction of magnetic moments (H = 0):  impact on lines of flux in a homogeneous magnetic field:  direction of magnetic moments (H = 0):  impact on lines of flux in a homogeneous magnetic field:
  22. 22. Weak Ferromagnetism: Antiferromagnetism Antiparallel magnetic spins in MnO.
  23. 23. Weak Ferromagnetism: Antiferromagnetism
  24. 24. Weak Ferromagnetism: Antiferromagnetism  Antiferromagnets do not find wide application in magnetic technologies because they do not have a net overall magnetization.
  25. 25. Strong Magnetism: Ferrimagnetism Ferrimagnetism  Spontaneous alignment of a part of the permanent magnetic dipoles within a domain in the crystal lattice (predominantly in one direction).  requirements: atoms with partially filled orbitals, crystal structure  magnetic moment: partial compensation results in a magnetization  permeability: μr >> 1 , χm > 0 (strong magnetism)  materials: ferrites: spinell type metal oxides (AB2O4) Ferrimagnetism  Spontaneous alignment of a part of the permanent magnetic dipoles within a domain in the crystal lattice (predominantly in one direction).  requirements: atoms with partially filled orbitals, crystal structure  magnetic moment: partial compensation results in a magnetization  permeability: μr >> 1 , χm > 0 (strong magnetism)  materials: ferrites: spinell type metal oxides (AB2O4)
  26. 26. Strong Magnetism: Ferrimagnetism  direction of magnetic moments (H = 0):  impact on lines of flux in a homogeneous magnetic field:  direction of magnetic moments (H = 0):  impact on lines of flux in a homogeneous magnetic field:
  27. 27. Strong Magnetism: Ferrimagnetism
  28. 28. Strong Magnetism
  29. 29. Magnetic Hysteresis
  30. 30. Initial Magnetization Curve J(H) and B (H) Curve
  31. 31. Magnetic Hysteresis
  32. 32. Magnetic Hysteresis  The suitability of ferromagnetic materials for particular applications is determined largely from characteristics shown by their hysteresis loops. For example-  a square-shaped hysteresis loop, with two stable magnetization states, is suitable for magnetic data storage;  a small hysteresis loop that is easily cycled between states is suitable for a transformer core with a rapidly switching field direction.  The suitability of ferromagnetic materials for particular applications is determined largely from characteristics shown by their hysteresis loops. For example-  a square-shaped hysteresis loop, with two stable magnetization states, is suitable for magnetic data storage;  a small hysteresis loop that is easily cycled between states is suitable for a transformer core with a rapidly switching field direction.
  33. 33. Domains  Domains form to minimize and in some cases to completely eliminate demagnetisation fields (HD); they are not random structures.  Domains form to minimize and in some cases to completely eliminate demagnetisation fields (HD); they are not random structures.
  34. 34. Schematic showing how formation of domains lowers the energy of the system, (a) No domains, (b) Two domains separated by a 180 wall, (c) The 90 domains are called closure domains because they result in the flux lines being completely enclosed within the solid. Closure domains are much more common in cubic crystals than in hexagonal ones because of the isotropy of the former
  35. 35. Alignment of individual magnetic dipoles within a 180o wall.
  36. 36. Soft and Hard Magnetism  All ferromagnetic materials are divided into two broad groups- soft and hard magnetic materials. Soft Magnetic Materials:  Materials, which have, a steeply rising magnetization curve, relatively small and narrow hysteresis loop and consequently small energy losses during cyclic magnetization are called soft magnetic materials.  All ferromagnetic materials are divided into two broad groups- soft and hard magnetic materials. Soft Magnetic Materials:  Materials, which have, a steeply rising magnetization curve, relatively small and narrow hysteresis loop and consequently small energy losses during cyclic magnetization are called soft magnetic materials.
  37. 37. Soft Magnetic Materials  Soft magnetic materials are therefore employed in building cores for use in alternating magnetic fields. Examples are nickel-iron alloy and soft ferrites.  Structure :Spinel (Cubic Ferrites) 1 MeO: 1Fe2O3 Me= Ni, Co, Mn, Zn  Soft magnetic materials are therefore employed in building cores for use in alternating magnetic fields. Examples are nickel-iron alloy and soft ferrites.  Structure :Spinel (Cubic Ferrites) 1 MeO: 1Fe2O3 Me= Ni, Co, Mn, Zn
  38. 38. Hard Magnetic Material  Magnetic materials, which have a gradually rising magnetisation curve, large hysteresis loop area and large energy losses for each cycle of magnetisation, are called hard magnetic materials.  Such materials are used for making permanent magnets. Examples are carbon steel, tungsten steel alnico.  Magnetic materials, which have a gradually rising magnetisation curve, large hysteresis loop area and large energy losses for each cycle of magnetisation, are called hard magnetic materials.  Such materials are used for making permanent magnets. Examples are carbon steel, tungsten steel alnico.
  39. 39. Hard Magnetic Material  Structure: Magnetoplumbite ( Hexagonal Ferrites) 1 MeO: 6Fe2O3 MeO= divalent materials BaO, CaO, SrO  Structure: Magnetoplumbite ( Hexagonal Ferrites) 1 MeO: 6Fe2O3 MeO= divalent materials BaO, CaO, SrO
  40. 40. Soft and Hard Magnetism
  41. 41. Soft and Hard Magnetism Type Industry where used Composition Soft Magnet Entertainment electronics, Mn, Zn, Fe oxides Radio communication Ni, Zn, Fe Oxides Military electronics Ni, Cu, Zn, Fe oxides Hard Maget Permanent motors Ba, Fe oxides, Sr, Pb,
  42. 42. Perovskite Metal Oxides  Ideal form of the crystal structure of cubic ABX3 perovskite consisting of corner sharing [BX6] octahedra with the A cation occupying the 12-fold coordination site formed in the middle of the cube of eight such octahedra.  The perovskite family of oxides is probably the best studied family of oxides.  The interest in compounds belonging to this family of crystal structures arise in the large and ever surprising variety of properties exhibited and the flexibility to accommodate almost all of the elements in the periodic system.  Ideal form of the crystal structure of cubic ABX3 perovskite consisting of corner sharing [BX6] octahedra with the A cation occupying the 12-fold coordination site formed in the middle of the cube of eight such octahedra.  The perovskite family of oxides is probably the best studied family of oxides.  The interest in compounds belonging to this family of crystal structures arise in the large and ever surprising variety of properties exhibited and the flexibility to accommodate almost all of the elements in the periodic system.
  43. 43. Perovskite Metal Oxides  Distorted perovskites have reduced symmetry, which is important for their magnetic properties. Thus leading towards great industrial importance.  Distorted perovskites have reduced symmetry, which is important for their magnetic properties. Thus leading towards great industrial importance.
  44. 44. Perovskite Metal Oxides  If the large oxide ion is combined with a metal ion having a small radius the resulting crystal structure can be looked upon as close packed oxygen ions with metal ions in the interstitials. This is observed for many compounds with oxygen ions and transition metals of valence +2, e.g. NiO, CoO, and MnO. In these crystal structures the oxygen ions form a cubic close packed lattice (ccp) with the metal ion in octahedral interstitials (i.e. the rock salt structure).  If the large oxide ion is combined with a metal ion having a small radius the resulting crystal structure can be looked upon as close packed oxygen ions with metal ions in the interstitials. This is observed for many compounds with oxygen ions and transition metals of valence +2, e.g. NiO, CoO, and MnO. In these crystal structures the oxygen ions form a cubic close packed lattice (ccp) with the metal ion in octahedral interstitials (i.e. the rock salt structure).
  45. 45. Perovskite Metal Oxides  Replacing one fourth of the oxygen with a cation of approximately the same radius as oxygen (e.g. alkali, alkali earth or rare earth element) reduces the number of octahedral voids, occupied by a small cation, to one fourth.  The chemical formula can be written as ABX3 and the crystal structure is called perovskite. X is often oxygen but also other large ions such as F– and Cl– are possible.  Replacing one fourth of the oxygen with a cation of approximately the same radius as oxygen (e.g. alkali, alkali earth or rare earth element) reduces the number of octahedral voids, occupied by a small cation, to one fourth.  The chemical formula can be written as ABX3 and the crystal structure is called perovskite. X is often oxygen but also other large ions such as F– and Cl– are possible.
  46. 46. Perovskite Metal Oxides  Most perovskites are distorted and do not have the ideal cubic structure.  Three main factors are identified as being responsible for the distortion: 1. Size effects, 2. deviations form the ideal composition and 3. Jahn-Teller effect. It is rare that a distortion of a certain perovskite compound can be assigned to a single effect. In most cases several factors act on the structure.  Most perovskites are distorted and do not have the ideal cubic structure.  Three main factors are identified as being responsible for the distortion: 1. Size effects, 2. deviations form the ideal composition and 3. Jahn-Teller effect. It is rare that a distortion of a certain perovskite compound can be assigned to a single effect. In most cases several factors act on the structure.
  47. 47. Perovskite Metal Oxides Outline of the ideal cubic perovskite structure SrTiO3 that has (a) a three dimensional net of corner sharing [TiO6] octahedra with (b) Sr2+ ions in the twelve fold cavities in between the polyhedra.
  48. 48. Perovskite Metal Oxides  Perovskites with transition metal ions (TMI) on the B site show an enormous variety of intriguing electronic or magnetic properties. This variety is not only related to their chemical flexibility, but also and to a larger extent related to the complex character that transition metal ions play in certain coordinations with oxygen or halides .  Perovskites with transition metal ions (TMI) on the B site show an enormous variety of intriguing electronic or magnetic properties. This variety is not only related to their chemical flexibility, but also and to a larger extent related to the complex character that transition metal ions play in certain coordinations with oxygen or halides .
  49. 49. Perovskite Metal Oxides  While magnetism and electronic correlations are usually related to unfilled 3d electron shells of the TMI, where as dielectric properties are connected with filled 3d electron shells.  While magnetism and electronic correlations are usually related to unfilled 3d electron shells of the TMI, where as dielectric properties are connected with filled 3d electron shells.
  50. 50. Perovskite Metal Oxides  Nevertheless, in the presence of competing interactions, canted moments or in composites large magneto- capacitive couplings have been reported.  To some extend these aspects also touch application areas, as e.g. capacitors, transducers, actuators, sensors and electrooptical switches.  Nevertheless, in the presence of competing interactions, canted moments or in composites large magneto- capacitive couplings have been reported.  To some extend these aspects also touch application areas, as e.g. capacitors, transducers, actuators, sensors and electrooptical switches.
  51. 51. Perovskite Metal Oxides  Magnetism or orbital (electronic) ordering phenomena of various kinds are observed in perovskites with TMI that have unfilled 3d electron shells.  Electronic correlations of such 3d states are generally strong, as the ratio Ud/W of the Coulomb repulsion energy Ud vs. the bandwidth W is larger compared to other electronic states, i.e. they have a more local character and a tendency for insulating states or metal-insulator transitions.  Hopping and superexchange of these electrons takes place via oxygen sites due to the overlap of the respective wave function. Thereby, the properties and phase diagrams of a perovskite strongly depend on nonstoichiometries and even more on tilting or distortions of the [BO6] octahedra.  Magnetism or orbital (electronic) ordering phenomena of various kinds are observed in perovskites with TMI that have unfilled 3d electron shells.  Electronic correlations of such 3d states are generally strong, as the ratio Ud/W of the Coulomb repulsion energy Ud vs. the bandwidth W is larger compared to other electronic states, i.e. they have a more local character and a tendency for insulating states or metal-insulator transitions.  Hopping and superexchange of these electrons takes place via oxygen sites due to the overlap of the respective wave function. Thereby, the properties and phase diagrams of a perovskite strongly depend on nonstoichiometries and even more on tilting or distortions of the [BO6] octahedra.
  52. 52. Perovskite Metal Oxides  Further aspects rely on order/disorder processes of the orbital part of the 3d wave function, charge doping and charge/orbital inhomogeneous states that lead to colossal response, e.g. to external magnetic fields.  Further aspects rely on order/disorder processes of the orbital part of the 3d wave function, charge doping and charge/orbital inhomogeneous states that lead to colossal response, e.g. to external magnetic fields.
  53. 53. Perovskite Metal Oxides  Before, however, considering such effects the properties of the system are given by a hierarchy of energies based on the electronic structure, i.e. 1. the number of 3d electrons, 2. the Hunds Rule coupling, 3. the crystalline electric field or Jahn-Teller splitting of the 3d electron states and 4. due to exchange energies.  Before, however, considering such effects the properties of the system are given by a hierarchy of energies based on the electronic structure, i.e. 1. the number of 3d electrons, 2. the Hunds Rule coupling, 3. the crystalline electric field or Jahn-Teller splitting of the 3d electron states and 4. due to exchange energies.
  54. 54. Magnetic Ferroelectric or Multiferroic  Magnetoelectrics are materials that are both ferromagnetic and ferroelectric in the same phase.  have a spontaneous magnetization that can be switched by an applied magnetic field, a spontaneous polarization that can be switched by an applied electric field, and often some coupling between the two.  Very few exist in nature or have been synthesized in the laboratory.  Magnetoelectrics are materials that are both ferromagnetic and ferroelectric in the same phase.  have a spontaneous magnetization that can be switched by an applied magnetic field, a spontaneous polarization that can be switched by an applied electric field, and often some coupling between the two.  Very few exist in nature or have been synthesized in the laboratory.
  55. 55. Magnetic Ferroelectric or Multiferroic  Multiferroism involves a number of subtle competing factors, with d-electron occupancy on the transition metal being a critical variable.  Multiferrocity, a coexistence of spontaneous ferroelectric and ferromagnetic moments, is a rare phenomenon due to the small number of low-symmetry magnetic point groups that allow a spontaneous polarization.  Multiferroism involves a number of subtle competing factors, with d-electron occupancy on the transition metal being a critical variable.  Multiferrocity, a coexistence of spontaneous ferroelectric and ferromagnetic moments, is a rare phenomenon due to the small number of low-symmetry magnetic point groups that allow a spontaneous polarization.
  56. 56. Applications  Permanent Magnet  Core, Transformer. Motor, Generator  Transducer: Nyquist Frequency, High Frequency  Data Storage etc.  Permanent Magnet  Core, Transformer. Motor, Generator  Transducer: Nyquist Frequency, High Frequency  Data Storage etc.
  57. 57. Engineering for Ferromagnets  FM-C-FM Structure (GMR)  Ferromagnet-Conductor-Ferromagnet Structure  The resistance of the conductor varies by FMs  Applications: Hard disk, MRAM, Magnetic sensors  FM-I-FM Structure (TMR)  Ferromagnet-Insulator-Ferromagnet Structure  The tunneling current through insulator varies by FMs  Larger MR ratio than GMR  Applications: MRAM  FM-S-FM Structure  Ferromagnet-Semiconductor-Ferromagnet Structure  Applications: Spin FET, LED  FM-C-FM Structure (GMR)  Ferromagnet-Conductor-Ferromagnet Structure  The resistance of the conductor varies by FMs  Applications: Hard disk, MRAM, Magnetic sensors  FM-I-FM Structure (TMR)  Ferromagnet-Insulator-Ferromagnet Structure  The tunneling current through insulator varies by FMs  Larger MR ratio than GMR  Applications: MRAM  FM-S-FM Structure  Ferromagnet-Semiconductor-Ferromagnet Structure  Applications: Spin FET, LED
  58. 58. Magnetic Storage Schematic representation showing how information is stored and retrieved using a magnetic storage medium
  59. 59. MRAM  Magnetic RAM
  60. 60. SCM (Storage Class Memory) Previous technology-  Memory (fast, expensive, volatile)  Storage (slow, cheap, non-volatile) By Storage Class Memory-  <200nsec (<1µ µµ µsec) Read/Write/Erase time  >100,000 Read I/O operations per second  Lifetime of 108 – 1012 write/erase cycles  10x lower power than enterprise HDD  No more than 3-5x the Cost of enterprise HDD (< $1 per GB in 2012) Previous technology-  Memory (fast, expensive, volatile)  Storage (slow, cheap, non-volatile) By Storage Class Memory-  <200nsec (<1µ µµ µsec) Read/Write/Erase time  >100,000 Read I/O operations per second  Lifetime of 108 – 1012 write/erase cycles  10x lower power than enterprise HDD  No more than 3-5x the Cost of enterprise HDD (< $1 per GB in 2012)
  61. 61. References  Book: Materials Science and Engineering: An Introduction; William D. Callister, Jr  Book: Fundamentals of Ceramics; M W Barsoum  Book: Modern Ceramic Engineering; David W. Richardson  Storage Class Memory, Technology and Use; IBM Almaden Research Center. 2008  Magnetic Control Device, And Magnetic Component and Memory Apparatus using the same,, Patent No: US 6,590,268 B2. 2003  Multiferroics: different ways to combine magnetism and ferroelectricity, D. Khomskii, Cologne University, Germany. 2006  Crystallography and Chemistry of Perovskites, Mats Johnsson and Peter Lemmens  Feature Article: Why Are There so Few Magnetic Ferroelectrics? Nicola A. Hill, University of California. 2000  Book: Materials Science and Engineering: An Introduction; William D. Callister, Jr  Book: Fundamentals of Ceramics; M W Barsoum  Book: Modern Ceramic Engineering; David W. Richardson  Storage Class Memory, Technology and Use; IBM Almaden Research Center. 2008  Magnetic Control Device, And Magnetic Component and Memory Apparatus using the same,, Patent No: US 6,590,268 B2. 2003  Multiferroics: different ways to combine magnetism and ferroelectricity, D. Khomskii, Cologne University, Germany. 2006  Crystallography and Chemistry of Perovskites, Mats Johnsson and Peter Lemmens  Feature Article: Why Are There so Few Magnetic Ferroelectrics? Nicola A. Hill, University of California. 2000

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