The document reports on the observation of microwave-assisted magnetization reversal (MAMR) in a 700 Gbit/in2 perpendicular recording media sample. MAMR was induced by applying microwave magnetic fields from a coplanar waveguide placed on the sample. For microwaves near the ferromagnetic resonance frequency of the media, MAMR occurred above a threshold microwave power. For high microwave power, MAMR was observed over a broad frequency range centered below the resonance frequency. Magnetic force microscopy images showed magnetization reversal in regions exposed to the microwaves. The results indicate microwave-assisted switching of grains in the perpendicular recording media.
Effects of Carbon Nanotube Dispersion on the
Material Properties of Polymer Matrix Composites by Azadeh Tavousi Tabatabaei, Seyed Hossein Mamanpush* and Bahareh Tavousi Tabatabaei in Evolutions in Mechanical Engineering
Performance Investigation and Enhancement of Fiber Bragg Gratingfor Efficient...IOSRJECE
In this paper, the performance of various windowfunctions for Fiber Bragg Grating Sensor (FBGS)is investigated and evaluated in order to get optimized reflection spectrum with high reflectivity and an efficient side lobe suppression for efficient sensing measurement applications.For this purpose, a wide range of design parameters which include grating length and refractive index modulation amplitudehas been chosen to evaluate the sensor design. The performances of the different windowfunctions have been then compared in terms of reflectivity, full width half maximum bandwidth (FWHM), and sidelobe level(SLL) so as to get the most suitable design parametersto be used for sensing measurement.The simulation results presented in this paper show the effectiveness of the optimizedFBG sensor, which can be further implemented for high performance sensing applications.
Effects of Carbon Nanotube Dispersion on the
Material Properties of Polymer Matrix Composites by Azadeh Tavousi Tabatabaei, Seyed Hossein Mamanpush* and Bahareh Tavousi Tabatabaei in Evolutions in Mechanical Engineering
Performance Investigation and Enhancement of Fiber Bragg Gratingfor Efficient...IOSRJECE
In this paper, the performance of various windowfunctions for Fiber Bragg Grating Sensor (FBGS)is investigated and evaluated in order to get optimized reflection spectrum with high reflectivity and an efficient side lobe suppression for efficient sensing measurement applications.For this purpose, a wide range of design parameters which include grating length and refractive index modulation amplitudehas been chosen to evaluate the sensor design. The performances of the different windowfunctions have been then compared in terms of reflectivity, full width half maximum bandwidth (FWHM), and sidelobe level(SLL) so as to get the most suitable design parametersto be used for sensing measurement.The simulation results presented in this paper show the effectiveness of the optimizedFBG sensor, which can be further implemented for high performance sensing applications.
Finite Element Analysis of Single Slot Antenna for Microwave Tumor AblationIOSR Journals
This study is aimed at investigating the characteristics of various slot sizes of microwave antenna suitable for ablation of hepatic and other tumors. The single slot antenna for hepatic MWA was designed using COMSOL MULTIPHYSICS 4.3b software. A total number of 140 antennas models were designed out of which one was selected based on the variation in its reflection coefficient, total power density and Specific Absorption Ratio. The three antennas have different geometry parameters based on the effective wavelength in liver tissue at 2.45GHz. The inner and outer conductors of the antenna were modeled using perfect electric conductor (PEC) boundary conditions. The model was simulated at multiple discrete lengths of slot between 2.5mm and 4.5mm, using 0.1mm increment to determine the antenna efficiency. The antenna has a reflection coefficient as low as -44.67618 dB, with a corresponding total power dissipation of 9.47744 W at slot size 3.5 mm. The results show that the antenna operates with low reflection coefficient which at high power levels prevents overheating of the feedline. Feedline overheating may damage the coaxial line, thereby making it is suitable for ablation of hepatic and other tumors
Profile of Single Mode Fiber Coupler Combining with Bragg GratingTELKOMNIKA JOURNAL
This paper describes a numerical experiment of design and operation of a fiber coupler between
single mode fiber and fiber Bragg grating (FBG). Both components are coupled depending with optical
waveguide and source parameters. A characterization of fiber coupler is simulated by varying long grating
of 10 mm to 60 mm using transfer matrix method based on coupled mode equation. The wave peak,
transmission, and dispersion parameters are analyzed to determine the performance of the fiber coupler.
The transmission spectrum showed the wave peaks rise to any increase in the grating length on channel
1 and channel 2. Transmission on channel 1 and channel 2 decreased from the wavelength range of
1.45μm–1.55μm and rised in the range of 1,55μm–1,65μm for each increment in length of grating. The
dispersion showed the zero dispersion at specific wavelength for each increase in length of grating. This
component can be applied for controlling information signal in wide range communication.
Design, Electrostatic and Eigen Frequency Analysis of Fixed– Fixed Beam MEMS ...IOSR Journals
The objective of this paper is to design of fixed–fixed MEMS Resonator. The beam of resonator is
made up of poly-silicon. This paper also presents the electrostatic and Eigen frequency analysis of MEMS
resonator. The resonator used in oscillator which can be fabricated on chip. It can also be used as Switch. The
size of crystal oscillator is in order of centimeter but the size of MEMS Resonator is in order of microns, so by
replace a crystal oscillator by MEMS Resonator, we can reduce the size of the system. The dc voltage is given to
the beam of resonator for electrostatic analysis & Eigen frequency analysis in different modes
Scanning electron microscopy (SEM) Likhith KLIKHITHK1
Scanning Electron Microscope functions exactly as their optical counterparts except that they use a focused beam of electrons instead of light to “image” the specimen and gain information as to its structure and composition. Given sufficient light, the unaided human eye can distinguish two points 0.2 mm apart. If the points are closer together, they will appear as a single point. This distance is called the resolving power or resolution of the eye. Similarly, light microscopes use visible light (400- 700nm) and transparent lenses to see objects as small as about one micrometer (one millionth of a meter), such as a red blood cell (7 μm) or a human hair (100 μm). Light microscope has a magnification of about 1000x and enables the eye to resolve objects separated by 200 nm. Electron Microscopes were developed due to the limitations of light microscopes, which are limited by the physics of light. Electron Microscopes are capable of much higher magnifications and have a greater resolving power than a light microscope, allowing it to see much smaller objects at sub cellular, molecular and atomic level. The smallest the wavelength of the illuminating sources is the best resolution of the microscope. De Broglie defined the wavelength of moving particles (electron) λ = h/mv, Where λ= wavelength of particles, h= Planck, s constant, m= mass of the particle (electron), v= velocity of the particles; after substituting the known values, λ = 12.3 Ao/V. The resolution of an optical microscope is defined as the shortest distance between two points on a specimen that can still be distinguished by the observer or camera system as separate entities. Resolution (r) = λ/ (2NA), Where λ is the imaging wavelength, NA is objective numerical aperture. Magnification is the process of enlarging the appearance, not physical size, of something. Magnification is defined as the ratio of image distance versus object distance. M= v/u, Where M= magnification, u= object distance, v= image distance. Magnification is also defined as the ratio of the resolving power of the eye to resolving power (δ) of the microscope M= δ eye/ δ microscope.
A SIMPLE METHOD TO AMPLIFY MICRO DISPLACEMENTijics
A simple method to amplify the micro displacements produced by magnetostrictive effect, giant
magnetostrictive, converse piezoelectric and photo strictive effect, respectively, is reported. The device
consists mainly of two material rods with different coefficients of strains vs intensity of external fields,
which are rigidly jointed, so that the displacements created by different rods can be added directly. In
contrast with all other methods reported so far, which are all based on the principle of lever, this approach
holds some unique advantages that can be applied to respond to the electromagnetic fields with high
frequency because there is no friction caused by the relative motion between levers and furthermore, an
ideal and smooth amplification of micro displacement can be obtained with ease in principle.
Transmission spectra of single ring coupled-waveguide resonator configuration...TELKOMNIKA JOURNAL
Development of optical waveguide resonators have greatly expanded and continues to grow since they have kinds potential applications such as wavelength filtering, switching, coupling and multiplexing. One of resonators, coupled waveguides, ring resonators are designed and operated using various coupling configurations. Ring resonators can be particularly used as wavelength filter if the wavelength can fit a whole multiple time in the circumference of the ring. This article proposes to investigate the transmission spectra from the power source and amplify it in linearized ring resonator configurations and varies the input amplitude on five different wavelengths. With finite difference time domain method, the geometry and power source are simulated to obtain the better result and configuration. The results show the intensity phenomena of filtering in optical circuit.
Core-cladding mode resonances of long period fiber grating in concentration s...IOSR Journals
Long period fiber grating (LPFG) is photoinduced fiber device that facilitates the coupling of core
mode to different cladding modes resulting into series of transmission dips in the transmission spectrum. Here
we present LPFG chemical sensor to determine the concentration of Manganese in water at ppm level. We
fabricated LPFG of period 600μm in single mode communication fiber using 12W carbon dioxide laser
applying point by point method. The fabricated LPFG is directly used as chemical sensor since cladding modes
coupled to core mode directly come in contact with surrounding chemicals. Concentration of manganese in our
collected sample is found to be 0.0329ppm. The result is verified with sophisticated Atomic Absorption
Spectrometer (AAS).
Andrii Sofiienko - Electron range evaluation and X-ray conversion optimizatio...Andrii Sofiienko
Electron range evaluation and X-ray conversion optimization in tungsten transmission-type targets with the aid of wide electron beam Monte Carlo simulations
Finite Element Analysis of Single Slot Antenna for Microwave Tumor AblationIOSR Journals
This study is aimed at investigating the characteristics of various slot sizes of microwave antenna suitable for ablation of hepatic and other tumors. The single slot antenna for hepatic MWA was designed using COMSOL MULTIPHYSICS 4.3b software. A total number of 140 antennas models were designed out of which one was selected based on the variation in its reflection coefficient, total power density and Specific Absorption Ratio. The three antennas have different geometry parameters based on the effective wavelength in liver tissue at 2.45GHz. The inner and outer conductors of the antenna were modeled using perfect electric conductor (PEC) boundary conditions. The model was simulated at multiple discrete lengths of slot between 2.5mm and 4.5mm, using 0.1mm increment to determine the antenna efficiency. The antenna has a reflection coefficient as low as -44.67618 dB, with a corresponding total power dissipation of 9.47744 W at slot size 3.5 mm. The results show that the antenna operates with low reflection coefficient which at high power levels prevents overheating of the feedline. Feedline overheating may damage the coaxial line, thereby making it is suitable for ablation of hepatic and other tumors
Profile of Single Mode Fiber Coupler Combining with Bragg GratingTELKOMNIKA JOURNAL
This paper describes a numerical experiment of design and operation of a fiber coupler between
single mode fiber and fiber Bragg grating (FBG). Both components are coupled depending with optical
waveguide and source parameters. A characterization of fiber coupler is simulated by varying long grating
of 10 mm to 60 mm using transfer matrix method based on coupled mode equation. The wave peak,
transmission, and dispersion parameters are analyzed to determine the performance of the fiber coupler.
The transmission spectrum showed the wave peaks rise to any increase in the grating length on channel
1 and channel 2. Transmission on channel 1 and channel 2 decreased from the wavelength range of
1.45μm–1.55μm and rised in the range of 1,55μm–1,65μm for each increment in length of grating. The
dispersion showed the zero dispersion at specific wavelength for each increase in length of grating. This
component can be applied for controlling information signal in wide range communication.
Design, Electrostatic and Eigen Frequency Analysis of Fixed– Fixed Beam MEMS ...IOSR Journals
The objective of this paper is to design of fixed–fixed MEMS Resonator. The beam of resonator is
made up of poly-silicon. This paper also presents the electrostatic and Eigen frequency analysis of MEMS
resonator. The resonator used in oscillator which can be fabricated on chip. It can also be used as Switch. The
size of crystal oscillator is in order of centimeter but the size of MEMS Resonator is in order of microns, so by
replace a crystal oscillator by MEMS Resonator, we can reduce the size of the system. The dc voltage is given to
the beam of resonator for electrostatic analysis & Eigen frequency analysis in different modes
Scanning electron microscopy (SEM) Likhith KLIKHITHK1
Scanning Electron Microscope functions exactly as their optical counterparts except that they use a focused beam of electrons instead of light to “image” the specimen and gain information as to its structure and composition. Given sufficient light, the unaided human eye can distinguish two points 0.2 mm apart. If the points are closer together, they will appear as a single point. This distance is called the resolving power or resolution of the eye. Similarly, light microscopes use visible light (400- 700nm) and transparent lenses to see objects as small as about one micrometer (one millionth of a meter), such as a red blood cell (7 μm) or a human hair (100 μm). Light microscope has a magnification of about 1000x and enables the eye to resolve objects separated by 200 nm. Electron Microscopes were developed due to the limitations of light microscopes, which are limited by the physics of light. Electron Microscopes are capable of much higher magnifications and have a greater resolving power than a light microscope, allowing it to see much smaller objects at sub cellular, molecular and atomic level. The smallest the wavelength of the illuminating sources is the best resolution of the microscope. De Broglie defined the wavelength of moving particles (electron) λ = h/mv, Where λ= wavelength of particles, h= Planck, s constant, m= mass of the particle (electron), v= velocity of the particles; after substituting the known values, λ = 12.3 Ao/V. The resolution of an optical microscope is defined as the shortest distance between two points on a specimen that can still be distinguished by the observer or camera system as separate entities. Resolution (r) = λ/ (2NA), Where λ is the imaging wavelength, NA is objective numerical aperture. Magnification is the process of enlarging the appearance, not physical size, of something. Magnification is defined as the ratio of image distance versus object distance. M= v/u, Where M= magnification, u= object distance, v= image distance. Magnification is also defined as the ratio of the resolving power of the eye to resolving power (δ) of the microscope M= δ eye/ δ microscope.
A SIMPLE METHOD TO AMPLIFY MICRO DISPLACEMENTijics
A simple method to amplify the micro displacements produced by magnetostrictive effect, giant
magnetostrictive, converse piezoelectric and photo strictive effect, respectively, is reported. The device
consists mainly of two material rods with different coefficients of strains vs intensity of external fields,
which are rigidly jointed, so that the displacements created by different rods can be added directly. In
contrast with all other methods reported so far, which are all based on the principle of lever, this approach
holds some unique advantages that can be applied to respond to the electromagnetic fields with high
frequency because there is no friction caused by the relative motion between levers and furthermore, an
ideal and smooth amplification of micro displacement can be obtained with ease in principle.
Transmission spectra of single ring coupled-waveguide resonator configuration...TELKOMNIKA JOURNAL
Development of optical waveguide resonators have greatly expanded and continues to grow since they have kinds potential applications such as wavelength filtering, switching, coupling and multiplexing. One of resonators, coupled waveguides, ring resonators are designed and operated using various coupling configurations. Ring resonators can be particularly used as wavelength filter if the wavelength can fit a whole multiple time in the circumference of the ring. This article proposes to investigate the transmission spectra from the power source and amplify it in linearized ring resonator configurations and varies the input amplitude on five different wavelengths. With finite difference time domain method, the geometry and power source are simulated to obtain the better result and configuration. The results show the intensity phenomena of filtering in optical circuit.
Core-cladding mode resonances of long period fiber grating in concentration s...IOSR Journals
Long period fiber grating (LPFG) is photoinduced fiber device that facilitates the coupling of core
mode to different cladding modes resulting into series of transmission dips in the transmission spectrum. Here
we present LPFG chemical sensor to determine the concentration of Manganese in water at ppm level. We
fabricated LPFG of period 600μm in single mode communication fiber using 12W carbon dioxide laser
applying point by point method. The fabricated LPFG is directly used as chemical sensor since cladding modes
coupled to core mode directly come in contact with surrounding chemicals. Concentration of manganese in our
collected sample is found to be 0.0329ppm. The result is verified with sophisticated Atomic Absorption
Spectrometer (AAS).
Andrii Sofiienko - Electron range evaluation and X-ray conversion optimizatio...Andrii Sofiienko
Electron range evaluation and X-ray conversion optimization in tungsten transmission-type targets with the aid of wide electron beam Monte Carlo simulations
Materi IQ, EQ, AQ, SQ merupakan materi penting dalam sebuah pembelajaran. seorang pemateri, motivator, guru harus mampu menumbuhkan Ke-empat potensi tersebut kepada siswa/peserta demi tercapainya pendidikan Islam
A dual-band metamaterial absorber comprised with two different resonators is presented in this letter. The proposed PMA shows two unity absorption peaks at 9 GHz and 11.8 GHz. Moreover, the absorber also manifests polarization insensitive response for resonator 1 and polarization controllable behavior for resonator 2. The effect of different oblique incidence angles has also been inspected for both the wave-excitation. The examined features reveal that this kind of PMA could be effectively used for multiband sensing applications in the X band of the microwave regime.
DETERMINATION OF BURIED MAGNETIC MATERIAL’S GEOMETRIC DIMENSIONSsipij
It is important to find buried magnetic material’s geometric features that are parallel to the soil surface in
order to determine anti-tank and anti-personnel mine compatible to standards. So that it is possible to
decrease the number of false alarms by separating the samples that have got non-standard geometries. For
this purpose, in this study the anomalies occurred at horizontal component of the earth’s magnetic field by
buried samples are determined with magnetic sensor. In the study, KMZ51 AMR is used as the magnetic
sensor. The position-controlled movement of the sensor along x-y axis is provided with 2D scanning system.
Trigger values of sensor output are evaluated with respect to the scanning field. The experiments are
redone for the samples at different geometries and variables are defined for geometric analysis. The
experimental conclusions obtained from this paper will be discussed in detail.
Qualitative analysis of Fruits and Vegetables using Earth’s Field Nuclear Mag...IJERA Editor
Among the imaging techniques, magnetic resonance imaging (MRI) is a non-contact and a non-invasive technique to obtain images of the objects rich in water content and provides an excellent tool to study variation of contrast among the soft issues. It often utilizes a linear magnetic field gradient to obtain an image that combines the visualization of molecular structure and dynamics. It measures the characteristics of hydrogen nuclei of water and nuclei with similar chemical shifts, modified by chemical environment across the object. In the present work, MRI of fresh tomatoes has been recorded using Terranova-MRI for qualitative analysis. The technique is effective, powerful and reliable as an investigative tool in the quality analysis and diagnosis of infections in fruits and vegetables.
Comparative Study of Evolutionary Algorithms for the Optimum Design Of Thin B...jmicro
With the increasing levels of Electromagnetic pollution almost exponentially in this modern age of
Electronics reported and highlighted by numerous studies carried out by scientists from all over the world,
inspire engineers to concentrate their research for the optimum design of multilayer microwave absorber
considering various parameters which are inherently conflicting in nature. In this paper we mainly focus
on the comparative study of different Evolutionary algorithms for the optimum design of thin broadband (2-
20GHz) multilayer microwave absorber for oblique incidence (300
) considering arbitrary polarization of
the electromagnetic waves. Different models are presented and synthesized using various Evolutionary
algorithm namely Firefly algorithm (FA), Particle swarm optimization (PSO), Artificial bee colony
optimization (ABC) and the best simulated results are tabulated and compared with each others.
The Modulation Transfer Function (MTF) of Polycrystalline Mercuric Iodide based flat panel
x-ray detectors is simulated as a function of spatial frequency. A simplified mathematical model for MTF is
applied on four different published prototypes of Polycrystalline Mercuric Iodide. Our aim was to fit curve from
MTF model with the curve from experimental data. The result of simulation from theoretical model shows a
good agreement with the measured data. We have found that deep-trapping,K-fluorescence,dependence of dark
current on temperature and exposure time are the most possible reasons for the slight mismatches between two
curves. In addition, the mobility-lifetime product for best curve fitting was also examined for each prototype.
MAGNETIZED PLASMA WITH FERROMAGNETIC GRAINS AS A VIABLE NEGATIVE REFRACTIVE I...ijrap
The propagation of electromagnetic waves in a cold magnetized plasma with ferromagnetic grains (MPFG)
in the high frequency domain is studied theoretically. The dispersion of MPFG which is controlled by the
simultaneous characterization of the permittivity and permeability tensors. is investigated theoretically and
numerically near the resonance frequency. It is found that MPFG becomes transparent for the waves that
cannot propagate in conventional magnetized electron-ion plasma. The refractive index of the waves
propagating parallel to the applied magnetic field is found to be negative for the extraordinary wave in
certain frequency domain. The results obtained show that in a narrow band of the super-high-frequency
range near the electron cyclotron frequency, MPFG possess all the known characteristics of negative
refractive index media, which would make it as a viable alternative medium to demonstrate the known and
predicted peculiar properties of media having negative index of refraction.
This paper present design of new type of electromagnetic damper or eddy current damper
which has advantages of no mechanical contact, higher reliability and stability, high efficiency and
compactness. By using this damper we can minimized damping of different masses and thereby damping
coefficient. The damper is composed of neodymium iron boron grade N 50 magnet .By using this damper I
found greater difference in damping when experimental result are compared with analytical result.
Magnetized Plasma with Ferromagnetic Grains as a Viable Negative Refractive I...ijrap
The propagation of electromagnetic waves in a cold magnetized plasma with ferromagnetic grains (MPFG)
in the high frequency domain is studied theoretically. The dispersion of MPFG which is controlled by the
simultaneous characterization of the permittivity and permeability tensors. is investigated theoretically and
numerically near the resonance frequency. It is found that MPFG becomes transparent for the waves that
cannot propagate in conventional magnetized electron-ion plasma. The refractive index of the waves
propagating parallel to the applied magnetic field is found to be negative for the extraordinary wave in
certain frequency domain. The results obtained show that in a narrow band of the super-high-frequency
range near the electron cyclotron frequency, MPFG possess all the known characteristics of negative
refractive index media, which would make it as a viable alternative medium to demonstrate the known and
predicted peculiar properties of media having negative index of refraction.
Analysis and simulations of optimal geometry shapes of the 4 and 9 nano hole ...IJECEIAES
The possibility to limit and manipulate photons at nanometer scales attracted a lot of interest for exciting applications from subwavelength in laser, biosensors, biomedical and optoelectronics devices, the sensor optical properties, however; are complex due to two resonances through propagating and localized surface plasmons. The optical properties of surface plasmons (SPs) at the resonant wavelength is depending on the geometrical nanostructure of materials. In this article, we used different geometry of nanoholes array, 4 and 9 nanoholes array in a metallic film gold nanoparticle with different thickness (20,50,100) nm on SiO2 substrate with refractive index 1.46, we designed two different geometries; 4- holes: hole radius r1=200 nm, period p1=600 nm; and 9- holes: r2=100 nm, period p2=300 nm. Transmission and reflection spectrum have been calculated and simulated by FDTD Lumerical program. From results are observed the effect of thickness is interesting, transmission is increased at (t=20nm) for two arrays. Furthermore, the number of hole and its area has an influence on optical transmission and other parameters (E, H, Ref) which are characteristics of design of metallic nanostructure. We can see that there is a peak value of the wavelength at 519 nm approximately to 73% strong light transmission with 4-NHA in the other hand wavelength of 519 nm transmission is 45% with 9-NHA. strong light transmission is hopeful for many applications (biomedical devices, nanoantennas and laser optical fiber).
MODELING OF PLANAR METAMATERIAL STRUCTURE AND ITS EFFECTIVE PARAMETER EXTRACTIONIAEME Publication
This paper is about designing a Metamaterial structure and the Scattering Parameter Extraction Method that has become a prime tool for Metamaterial characterization so that there is a better understanding of relation between their configuration and associated properties of these materials in terms of negative permittivity and negative permeability to explore application potential. A 2D planar Metamaterial structure has been designed, fabricated and analyzed. It consists of conducting patches and meander lines on a dielectric substrate. Electromagnetic modeling was carried out using Finite Difference Time Domain method based simulation tool EMPIRE XCcel.
In metallurgy, cladding refers to the bonding together of dissimilar metals, normally achieved by extruding two or more metals through a die or pressing sheets together under high pressure. Timely detection of delamination that occurs occasionally during the cladding processes is very important for the industry. This paper presents an EMAT system based on ultrasonic guided wave techniques. The analysis of a three-layer, brass/copper/brass product is also presented including dispersion curves, and interaction of ultrasonic guided wave with delamination defects. The authors observed a cyclic behavior of guided wave propagation with the increase of defect size. An explanation is introduced and proved with finite element analysis. The results presented in this paper will have a very significant impact on understanding of delamination detection in multilayered composite structures including adhesive bonded structures.
Microstrip line discontinuities simulation at microwave frequencies
2013_APL_v103_p042413
1. Observation of microwave-assisted magnetization reversal in perpendicular
recording media
Lei Lu, Mingzhong Wu, Michael Mallary, Gerardo Bertero, Kumar Srinivasan et al.
Citation: Appl. Phys. Lett. 103, 042413 (2013); doi: 10.1063/1.4816798
View online: http://dx.doi.org/10.1063/1.4816798
View Table of Contents: http://apl.aip.org/resource/1/APPLAB/v103/i4
Published by the AIP Publishing LLC.
Additional information on Appl. Phys. Lett.
Journal Homepage: http://apl.aip.org/
Journal Information: http://apl.aip.org/about/about_the_journal
Top downloads: http://apl.aip.org/features/most_downloaded
Information for Authors: http://apl.aip.org/authors
2. Observation of microwave-assisted magnetization reversal in perpendicular
recording media
Lei Lu,1
Mingzhong Wu,1,a)
Michael Mallary,2
Gerardo Bertero,2
Kumar Srinivasan,2
Ramamurthy Acharya,2
Helmut Schultheiß,3
and Axel Hoffmann3
1
Department of Physics, Colorado State University, Fort Collins, Colorado 80523, USA
2
Western Digital Technologies, San Jose, California 92630, USA
3
Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
(Received 19 March 2013; accepted 12 July 2013; published online 25 July 2013)
This letter reports microwave-assisted magnetization reversal (MAMR) in a 700-Gbit/in2
perpendicular media sample. The microwave fields were applied by placing a coplanar waveguide on
the media sample and feeding it with narrow microwave pulses. The switching states of the media
grains were measured by magnetic force microscopy. For microwaves with a frequency close to the
ferromagnetic resonance (FMR) frequency of the media, MAMR was observed for microwave power
higher than a certain threshold. For microwaves with certain high power, MAMR was observed for a
broad microwave frequency range which covers the FMR frequency and is centered below the FMR
frequency. VC 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4816798]
In the presence of microwave magnetic fields, magnet-
ization reversal or switching in magnetic materials can be
realized with relatively low magnetic fields. This effect is
called microwave-assisted magnetization reversal (MAMR).
The MAMR effect was first observed by Thirion et al. in
2003.1
They demonstrated microwave-assisted switching in
a 20-nm cobalt particle using superconducting quantum in-
terference device (SQUID) techniques. Following the experi-
ments by Thirion et al., the MAMR effect was demonstrated
in a wide variety of magnetic elements or structures. These
include (i) single-domain elements, such as micron- and
submicron-sized permalloy film elements,2,3
permalloy nano
dots,4
submicron cobalt particles,5
and cobalt nanoparticles
with a diameter of only 3 nm,6,7
and (ii) multi-domain ele-
ments, such as cobalt strips,8
permalloy wires,9,10
permalloy
and FeCo thin films,11–13
permalloy layers in magnetic tun-
nel junctions,14,15
and Co/Pt multilayered structures.16–18
The experiments on these elements all demonstrate that the
application of appropriate microwaves can remarkably
reduce the magnetic field required for the magnetization re-
versal. The underlying physics for this MAMR response is as
follows: The microwave magnetic fields excite large-angle
magnetization precession; the large-angle precession lowers
the energy barrier for the rotation reversal in single-domain
elements and that for domain nucleation in multi-domain
materials.
In addition to its interesting fundamental physics, the
MAMR effect is also a very promising mechanism for the
realization of next-generation magnetic recording at several
terabits per square inch. Numerical simulations have demon-
strated the feasibility of MAMR operation in perpendicular
recording media.19,20
Experimental demonstrations, how-
ever, are rather challenging, as the media typically require
relatively large switching fields and have substantially larger
damping in comparison with the above-mentioned magnetic
materials. Nevertheless, very recently two groups reported
the studies of MAMR in perpendicular media. Boone et al.
used the anomalous Hall effect (AHE) to measure the hyster-
esis loop of a perpendicular media bar and studied the effects
of microwaves on the AHE loop.21,22
They observed a
microwave-caused reduction in the coercivity field of up to
8%. Nozaki et al. demonstrated that the exposure of a per-
pendicular media sample to microwaves could produce a no-
table shift in the sample’s ferromagnetic resonance (FMR)
field, which indicated the microwave-assisted switching of
certain grains in the sample.23
These two studies indicated
the feasibility of MAMR in perpendicular media.
This letter reports on the observation of MAMR
responses in a sample cut from a commercial quality 700-
Gbit/in2
media disk. Narrow microwave field pulses were
applied by placing a coplanar waveguide (CPW) structure on
the media sample. The switching states of the grains in the
media were measured by magnetic force microscopy
(MFM). For the microwaves with a frequency close to the
FMR frequency of the media, the microwave-assisted
switching was observed when the microwave power was
higher than a certain threshold level. For the microwaves
with a certain high power level, the MAMR was observed
for a relatively wide microwave frequency range which cov-
ers the FMR frequency but is centered at a frequency below
the FMR frequency. The effects of both the microwave pulse
duration and repetition rate were also examined. The results
indicated that the observed MAMR response was not attrib-
uted to heating effects.
The sample was a 4 mm by 4 mm rectangle element cut
from an exchange coupled composite (ECC) media disk. The
core components of the ECC media include a 4.5-nm-thick
“soft” magnetic layer, an 8.5-nm-thick “hard” magnetic
layer, and a 0.8-nm-thick weakly magnetic exchange-break
layer in-between the “soft” and “hard” layers. Both of the
two magnetic layers are CoPtCr-based granular films.
Figure 1 shows the static and FMR properties of the
sample. Graph (a) presents a hysteresis loop measured by
SQUID techniques. The measurement was carried out with a
static magnetic field (H) normal to the sample plane. The
a)
Author to whom correspondence should be addressed. Electronic mail:
mwu@lamar.colostate.edu
0003-6951/2013/103(4)/042413/5/$30.00 VC 2013 AIP Publishing LLC103, 042413-1
APPLIED PHYSICS LETTERS 103, 042413 (2013)
3. data indicate a saturation induction (4pMs) of about 9.2 kG, a
nucleation field in the 2–3 kOe range, and a coercivity field
of about 5.4 kOe. There is also a vertical dashed line in (a),
which indicates the strength of the switching field used in the
MAMR experiments. Graphs (b) and (c) present the FMR
data measured by broadband vector network analyzer techni-
ques.24
Graph (b) shows the (static) FMR field as a function
of frequency (f). The circles show the data, while the line
shows a fit to the Kittel equation
f ¼ jcjðH þ HintÞ; (1)
where |c| is the absolute gyromagnetic ratio. The term Hint
denotes an effective internal field, which is the sum of the
perpendicular magneto-crystalline anisotropy field (Ha), the
dipolar field, and the intergranular exchange field. One can
see that the fitting in graph (b) is almost perfect. The fitting
yielded |c| ¼ 3.28 GHz/kOe and Hint ¼ 7.4 kOe. Note that the
gyromagnetic ratio here is higher than the standard value
(2.8 GHz/kOe). Similar ratios were also reported for CoCrPt
alloy films25
and CoCr granular films.26
Note also that
Hint ¼ 7.4 kOe indicates an anisotropy field of Ha % 16.6 kOe
if one assumes Hint % Ha-4pMs. Graph (c) presents the half-
power FMR linewidth (DH) as a function of f. The circles
show the data, while the line shows a linear fit to
DH ¼
2a
jcj
f þ DH0; (2)
where a is the effective Gilbert damping parameter and DH0
describes sample inhomogeneity-caused line broadening.
The fitting yielded a ¼ 0.061 6 0.003 and DH0 ¼ 761
6 64 Oe. The a value is close to that reported for CoPtCr
alloy films (0.06).27
The inhomogeneity line broadening is
relatively large and is mainly attributed to the variation of
Hint on individual grains.28
The ratio of DH0 to Hint is about
10%, which is close to the switching field distribution of the
sample (7%–8%).29
Figure 2 illustrates the experimental approach. Graph
(a) shows a schematic of the experimental configuration.
Graphs (b) and (c) show a photograph and an atomic force
microscopy (AFM) image, respectively, of the portion of the
CPW structure where the signal line is a 5.5-lm-wide, 100-
lm-long narrow strip. Graph (d) gives a representative MFM
image of the media. The bright strip shows the region where
the media surface was in contact with the CPW signal line
and the grains were switched, due to the MAMR operation.
Graph (e) presents the two MFM images of the media show-
ing opposite contrasts. The left image was taken from an
area in the media where the MAMR operations were con-
ducted at four different locations. The four bright strips in
the image show the regions where the media grains are
switched due to the MAMR effect. The right image in (e)
was taken from an area where the MAMR operations were
carried out at two locations. The two dark strips show the
regions where the MAMR effect resulted in the switching.
For both the cases, the MAMR operations were carried out at
the same conditions except that for the right image (1) the
media sample was initially saturated in an opposite direction
and (2) the switching field during the MAMR operations was
also in an opposite direction, in comparison to the left
image.
The MAMR experiments consist of the following four
steps. (1) Saturate the media sample with a strong perpendic-
ular magnetic field. (2) Apply a switching field which is op-
posite to the magnetization in the media and is close to the
nucleation field (lower than the coercivity field). (3) Apply
microwave pulses to the CPW to assist the switching of the
grains in the media. (4) Turn off both the switching field and
the microwave signals and use the MFM system to determine
the switching status of the grains in the media. When the
FIG. 1. Properties of the ECC media
sample. (a) A hysteresis loop. (b) FMR
field vs. frequency. (c) FMR linewidth
vs. frequency.
042413-2 Lu et al. Appl. Phys. Lett. 103, 042413 (2013)
4. microwave pulses are applied, the narrow portion of the
CPW signal line (see Fig. 2(c)) produces relatively strong
microwave magnetic fields. These microwave fields lower
the energy barrier for magnetization reversal in the grains
right above the signal line and thereby induce the switching
of these grains. Such switching manifests itself as a bright
strip in the MFM image, as shown in Fig. 2(d) and in the left
graph of Fig. 2(e), or a dark strip, as shown in the right graph
of Fig. 2(e).
Three facts should be pointed out. First, the bright strip
in the MFM image in Fig. 2(d) has the same length and width
as the narrow signal line of the CPW. Second, towards the
left end of the bright strip in the MFM image in Fig. 2(d),
one sees a gradual increase in the strip width and a gradual
decrease in the strip contrast. This agrees with the expecta-
tions that the wider the signal line is, the weaker the micro-
wave field is and the fewer grains are switched. Third, the
MFM image shows a completely opposite contrast if one ini-
tially saturates the media along the opposite directions, as
shown in Fig. 2(e). These facts together clearly demonstrate
the validity of the above-described MAMR measurement
approaches.
Figures 3 and 4 show the core results of this work. The
MFM image in Fig. 3 was taken from a 100 lm  100 lm
square area of the sample where six separate MAMR experi-
ments were conducted at six different locations. The micro-
wave power Pmw used for each MAMR experiment is
indicated at the corresponding location. For all the experi-
ments, the carrier frequency fmw of the microwave pulse was
kept the same, at 13 GHz. For the MFM images in Fig. 4, in
contrast, the MAMR experiments at different locations were
carried out at the same microwave power, which was
31 dBm, but different microwave frequencies, as indicated.
Except for Pmw and fmw, the other parameters were the same
for all the experiments. The field used to saturate the sample
was 20 kOe. The switching field Hsw was 3 kOe. The micro-
wave pulses had a width of 11 ns and a repetition rate of
0.1 kHz. Note that the power levels cited above are nominal
power applied to the CPW. The field values given in Fig. 3
and below are microwave magnetic fields from the narrow
CPW signal line, which were estimated based on the input
microwave power, the reflection coefficient of the CPW, and
the width of the CPW signal line. The dashed lines in Fig. 4
indicate the positions of the CPW signal line in the corre-
sponding experiments.
The MFM image in Fig. 3 shows strips with rather low
contrasts for Pmw ¼ 23 dBm and 25 dBm and strips with high
contrasts for Pmw ! 27 dBm. This indicates a power thresh-
old of about 27 dBm (109 Oe) for MAMR operations with
microwave pulses of fmw ¼ 13 GHz. The MFM images in
Fig. 4 show high-contrast strips for fmw ¼ 8 GHz, 9 GHz,
10 GHz, 11 GHz, 12 GHz, 13 GHz, 14 GHz, and 15 GHz but
FIG. 3. An MFM image of the area of a media sample where six separate
MAMR experiments were carried out at six different locations. The micro-
wave power level used in each experiment is indicated at the corresponding
location.
FIG. 2. (a) Experimental configuration.
(b) A photograph of the portion of the
CPW where the signal line is narrow.
(c) An AFM image of the CPW signal
line. (d) An MFM image of the media
sample which shows the MAMR
effect. (e) Two MFM images which
show MAMR-caused strips but have
opposite contrasts.
042413-3 Lu et al. Appl. Phys. Lett. 103, 042413 (2013)
5. show no strips for fmw ¼ 5 GHz, 6 GHz, 7 GHz, 17 GHz,
and 19 GHz. This indicates that when Pmw ¼ 31 dBm, the
MAMR occurs over a frequency range of 8–15 GHz. Note
that according to Eq. (1) and the parameters cited above, the
field Hsw corresponds to an FMR frequency of 14.4 GHz for
the media, which is within the 8–15 GHz frequency range.
These results clearly demonstrate the MAMR operation
in the media. Moreover, they show that, for certain high
microwave power, the MAMR operation can take place over
a relatively broad frequency range which covers the FMR
frequency but is centered below the FMR frequency. This
agrees with previous experimental observations.21–23
The
reason for such a broad frequency range is due to the fact
that the media have a rather broad FMR linewidth as shown
in Fig. 1(c). The broad FMR field linewidth indicates a broad
FMR linewidth in the frequency domain. At 14 GHz, for
example, the above cited damping parameter corresponds to
a frequency linewidth of about 1.7 GHz; the field linewidth
DH0 corresponds to a frequency linewidth of about 2.5 GHz.
The broad linewidth in the frequency domain indicates that
the microwaves can drive the magnetization to precess over
a broad frequency range as long as the microwave field is
sufficient strong. Also, one can expect that this frequency
range increases with an increase in the microwave power.
The observation that the frequency range is centered below
the FMR frequency is mainly due to the fact that during the
switching process, the anisotropy field takes lower values
since the projection of the magnetization along the sample
normal direction is reduced. As the anisotropy field is
smaller, the effective internal field is smaller, and the preces-
sion frequency is also smaller during the switching.
Figure 5 presents representative MFM images that show
the effects of the microwave pulse repetition rate and dura-
tion. The left image shows four strips resulted from MAMR
with microwave pulses of the same duration (98 ns) but sig-
nificantly different repetition rates, as indicated. The right
images show two strips resulted from MAMR with micro-
wave pulses of the same repetition rate (0.1 kHz) but signifi-
cantly different durations, as indicated. The field used to
saturate the sample and the switching field was the same as
cited above. The microwave pulses had fmw ¼ 13 GHz and
Pmw ¼ 31 dBm. The strips in each image show almost the
same contrast. This demonstrates that the effects of the
microwave pulse repetition rate and duration are negligible.
This result indicates that the above-presented MAMR
responses were not attributed to a heating effect. Besides, the
closeness of the MAMR responses for two different micro-
wave pulse durations also indicates that the switching time is
no longer than 11 ns. Note that 11-ns-wide pulses are the nar-
rowest microwave pulses available in the authors’ labora-
tory. Future work on MAMR experiments with narrower
pulses is of great interest.
Three important points should be emphasized. (1) This
work made use of MFM techniques rather than the AHE and
FMR techniques used in previous work,21–23
to directly mea-
sure the switching status of the grains in the media in the
presence of microwaves. In this sense, this work presents a
direct demonstration for MAMR in perpendicular media. (2)
The data presented above were obtained from a commercial
quality 700-Gbit/in2
media disk sample rather than custom-
ized samples. Thus, this work is of practical significance. (3)
The data reveal the connection of the frequency response of
the MAMR operation to the FMR frequency as well as the
microwave power required by the MAMR operation for per-
pendicular media. These results provide far-reaching impli-
cations for the future of microwave-assisted magnetic
recording using perpendicular media.
In summary, this work demonstrated MAMR operation in
a 700-Gbit/in2
perpendicular media sample. For microwaves
with a frequency close to the FMR frequency of the media,
the MAMR operation was observed for microwave power
higher than a certain threshold level. For microwaves with
certain high power, the MAMR effects were observed for a
broad microwave frequency range which covers the FMR fre-
quency and is centered below the FMR frequency. It was also
demonstrated that the MAMR operation was independent of
both the microwave pulse duration and repetition rate.
This work was supported in part by the U. S. National
Institute of Standards and Technology (60NANB10D011)
FIG. 5. MFM images for the areas of a sample where separate MAMR
experiments were carried out at different locations. Left: the experiments
were carried out with microwave pulses of different repetition rates, as indi-
cated. Right: the experiments were carried out with microwave pulses of dif-
ferent durations, as indicated
FIG. 4. MFM images for the areas of a sample where separate MAMR experi-
ments were carried out at different locations. The experiments were carried
out with microwave pulses of different carrier frequencies, as indicated.
042413-4 Lu et al. Appl. Phys. Lett. 103, 042413 (2013)
6. and Western Digital Technologies. Work at Argonne and use
of the Center for Nanoscale Materials was supported by the
U.S. Department of Energy, Office of Basic Energy Sciences
(DE-AC02-06CH11357).
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