28th International Spring Seminar on Electronics Technology: Meeting the Challenges of Electronics Technology Progress, 2005.
A new magneto-optic angular displacement (MOAD) sensor is reported for measuring small angular an... more A new magneto-optic angular displacement (MOAD) sensor is reported for measuring small angular and spatial displacements of the surfaces of the material remotely. It is based on observation of changes in the intensity of the reflected polarized light beam, which passes through a magneto-optic (MO) thin garnet film with the controlled periodical displacement of one domain wall. Using Jones matrices for optical elements in the MOAD sensor system, simulated intensity of the MOAD sensor was obtained and compared with experimentally detected intensity. Results from simulation are in good agreement with experimental values. The MOAD sensor allows observation of angular displacement of a material located remotely from the laser and detector with resolution of 0.01deg
Magnetic particle inspection (MPI) is a widely used nondestructive inspection method for aerospac... more Magnetic particle inspection (MPI) is a widely used nondestructive inspection method for aerospace applications essentially limited to experiment-based approaches. The analysis of MPI characteristics that affect sensitivity and reliability contributes not only reductions in inspection design cost and time but also improvement of analysis of experimental data. The material is assumed to have isotropic ferromagnetic properties in this research. The
The electronic structure of Yb implanted ZnO has been studied by the resonant photoemission spect... more The electronic structure of Yb implanted ZnO has been studied by the resonant photoemission spectroscopy (RPES). The contribution of Yb 4f partial density of states (PDOS) is predominant in the binding energy (BE) about 7.5 and ~11.7 eV below the VB maximum. At the resonance energy, around 182 eV, the multiplet structure with the highest BE shows the strongest resonance (around 11.7 eV) that corresponds to the 1 I multiplet which is almost exclusively responsible for this resonance, while 3 H and 3 F states are responsible for the resonance around 7.5 eV. It was also found that the Yb 4f PDOS distribution shows some similarity to Yb2O3.
The Preisach model formalism has been applied to analyse hysteresis measurement results for evalu... more The Preisach model formalism has been applied to analyse hysteresis measurement results for evaluating fatigue damage in Fe-C alloys caused by cyclic fatigue loading. Hysteresis loops and differential permeability curves were measured at various stages of the fatigue life of the samples. The parameters which were built by means of the PMF and the classical hysteresis magnetic parameters (such as
The influence of different heat treatments on the magnetic and magnetoelastic properties of highl... more The influence of different heat treatments on the magnetic and magnetoelastic properties of highly magnetostrictive CoFe 2 O 4 has been investigated. The first order cubic anisotropy coefficient, coercive field, magnetostriction and high strain sensitivity were observed to decrease as the heat treatment temperature increased. The saturation magnetization of the samples on the other hand increased with increase in heat treatment temperature. These changes were not accompanied by any observable changes in crystal structure or composition and are indicative of migration of Co 2 + from the octahedral sites (B-sites) to the tetrahedral sites (A-sites) and Fe 3 + from the A-sites to the B-sites of the spinel structure. Different distributions of the cations at the two distinct lattice sites can strongly affect the magnetic and magnetoelastic properties of these materials.
Differences in the microstructure and magnetic properties of highly magnetostrictive cobalt ferri... more Differences in the microstructure and magnetic properties of highly magnetostrictive cobalt ferrite resulting from the effects of different vacuum sintering temperatures and times have been investigated. A vacuum environment was chosen to allow direct comparison of results with air-sintered samples which are more often reported in the literature. It was found that vacuum sintering resulted in the development of a solid solution second phase with composition Co 1Àx Fe x O 4 (x$0.33). There was a decrease in magnetostriction as a result of the formation of the second phase. Furthermore, differences in sintering temperatures were found to have a greater effect on the magnetostriction than differences in sintering times. It was found that the first order cubic anisotropy coefficient initially increased with both sintering temperature and time, before peaking and decreasing to its lowest measured value. The lowest anisotropy was therefore achieved with samples sintered at higher temperatures and longer times.
Gd 5 (Si x Ge 1 À x) 4 , known for its giant magnetocaloric effect, also exhibits a colossal stra... more Gd 5 (Si x Ge 1 À x) 4 , known for its giant magnetocaloric effect, also exhibits a colossal strain of the order of 10,000 ppm for a single crystal near its coupled first-order magnetic-structural phase transition, which occurs near room temperature for the compositions 0.41 r x r 0.575. Such colossal strain can be utilised for both magnetic sensor and actuator applications. In this study, various measurements have been carried out on strain as a function of magnetic field strength and as a function of temperature on single crystal Gd 5 Si 2 Ge 2 (x ¼ 0.5), and polycrystalline Gd 5 Si 1.95 Ge 2.05 (x ¼ 0.487) and Gd 5 Si 2.09 Ge 1.91 (x ¼ 0.52). Additionally a giant magnetostriction/thermally induced strain of the order of 1800 ppm in polycrystalline Gd 5 Si 2.09 Ge 1.91 was observed at its first order phase transition on varying temperature using a Peltier cell without the use of bulky equipment such as cryostat or superconducting magnet.
We have investigated the magnetic properties of a Co 36 Fe 36 Si 4 B 20 Nb 4 alloy developed for ... more We have investigated the magnetic properties of a Co 36 Fe 36 Si 4 B 20 Nb 4 alloy developed for high temperature soft magnetic applications. Studies of the crystallization of the alloy, prepared in the form of amorphous ribbons by melt-spinning, were performed using differential scanning calorimetry and X-ray diffraction. These studies, and further validation by transmission electron microscopy, suggested the formation of ðCoFeÞ 2 Si nanoparticles dispersed in an amorphous matrix during the first stage of crystallization which occurred at around 845 K. The formation of this nanocrystalline state by annealing at temperatures between 825 and 875 K not only raised the Curie temperature of the material to above 1000 K but also gave superior soft magnetic properties with a coercivity less than 50 A/m (625 mOe). However, at higher annealing temperatures, formation of strongly anisotropic phases with out of plane domain magnetization, observed by magnetic force microscopy, resulted in deterioration of the soft magnetic properties.
Determination of Curie temperature by plotting magnetic moment vs. temperature curves requires a ... more Determination of Curie temperature by plotting magnetic moment vs. temperature curves requires a small applied field, which influences the measurement and temporarily disturbs the temperature of the sample especially for highly magnetocaloric materials. The Arrott plot technique was therefore used in order to determine the Curie temperature for a magnetocaloric Gd5Si2. 7Ge1. 3 (x= 0.675) single crystal sample. This technique was compared with other methods such as the inflection point technique and the line ...
ABSTRACT The Jiles-Atherton (JA) theory of hysteresis has been extended in the present paper to m... more ABSTRACT The Jiles-Atherton (JA) theory of hysteresis has been extended in the present paper to model hysteresis in two-phase magnetic materials. Two-phase materials are those that exhibit two magnetic phases in one hysteresis cycle: one at lower fields and the other at higher fields. In magnetic hysteresis, the transition from one phase to the other i.e. low field phase to high field phase depends mainly on the exchange field. Hence, the material-dependent microstructural parameters of JA theory: spontaneous magnetization, M S , pinning factor, k , domain density, a , domain coupling, alpha , and reversibility factor, c , are represented as functions of the exchange field. Several cases based on this model have been discussed and compared with the measured data from existing literature. The shapes of the calculated and measured hysteresis loops are in excellent agreement.
Computer simulations were used to investigate the performance of a microscale ferrofluid-based ma... more Computer simulations were used to investigate the performance of a microscale ferrofluid-based magnetic actuator developed for liquid dispensing in microfluidic channels. The actuation was based on the movement of a ferrofluid plug in a magnetic field gradient generated by on-chip effectively infinite parallel conductors. The movement, positioning, and retaining of ferrofluid plugs with different lengths at various locations along a microfluidic channel were investigated for two cases. In case (a), the magnetic field gradient was generated by a single conductor; when the ferrofluid reached its equilibrium position, the current was switched off and the nearest neighbor conductor was energized. A similar, consecutive on/off current switching was performed for case (b), where a set of conductors was energized simultaneously.
Gd 5 ͑Si x Ge 1−x ͒ 4 for 0.41ഛ x ഛ 0.5 is orthorhombic and ferromagnetic at lower temperature, m... more Gd 5 ͑Si x Ge 1−x ͒ 4 for 0.41ഛ x ഛ 0.5 is orthorhombic and ferromagnetic at lower temperature, monoclinic and paramagnetic at higher temperature, and shows a first order magnetic-structural phase transition between the two. Magnetic moment versus magnetic field ͑MH͒ isotherms were measured just above the first order transition temperature for Gd 5 Si 1.95 Ge 2.05 and Gd 5 Si 2 Ge 2 samples and the field-induced coupled phase transition from paramagnetic/monoclinic to ferromagnetic/ orthorhombic phase was observed. Using the method developed by Arrott ͓Phys. Rev. 108, 1394 ͑1957͔͒, the ferromagnetic portions of the MH isotherms were used to project the second order magnetic phase transition temperature of the orthorhombic phase, a region where the transition does not occur due to the first order transition at a lower temperature. These data points fall on the extrapolated line of the second order phase transition, drawn from the Si-rich region of the phase diagram.
ABSTRACT Abstract–$rm Gd\_5({rm Si\_rm xrm Ge\_1-rm x\})_4\$ exhibits a first order phase transit... more ABSTRACT Abstract–$rm Gd\_5({rm Si\_rm xrm Ge\_1-rm x\})_4\$ exhibits a first order phase transition for the compositions $0<rm x<0.575$ leading to a magnetic phase transition as well. It is not possible to measure the second order phase (magnetic) transition temperatures of the individual phases with direct measurements. This is because the first order phase transition occurs before the second order phase transition. With modified Arrott plots we have shown previously that it is possible to estimate the second order phase transition of the $rm Gd\_5rm Si\_4\$ -type orthorhombic phase. In this paper we have estimated the second order phase transition temperature of the $rm Gd\_5rm Si\_2rm Ge\_2\$-type monoclinic phase using a single crystal sample of $rm Gd\_5rm Si\_1.5rm Ge\_2.5\$ (0.375) which falls in the mixed phase region of the sample.
28th International Spring Seminar on Electronics Technology: Meeting the Challenges of Electronics Technology Progress, 2005.
A new magneto-optic angular displacement (MOAD) sensor is reported for measuring small angular an... more A new magneto-optic angular displacement (MOAD) sensor is reported for measuring small angular and spatial displacements of the surfaces of the material remotely. It is based on observation of changes in the intensity of the reflected polarized light beam, which passes through a magneto-optic (MO) thin garnet film with the controlled periodical displacement of one domain wall. Using Jones matrices for optical elements in the MOAD sensor system, simulated intensity of the MOAD sensor was obtained and compared with experimentally detected intensity. Results from simulation are in good agreement with experimental values. The MOAD sensor allows observation of angular displacement of a material located remotely from the laser and detector with resolution of 0.01deg
Magnetic particle inspection (MPI) is a widely used nondestructive inspection method for aerospac... more Magnetic particle inspection (MPI) is a widely used nondestructive inspection method for aerospace applications essentially limited to experiment-based approaches. The analysis of MPI characteristics that affect sensitivity and reliability contributes not only reductions in inspection design cost and time but also improvement of analysis of experimental data. The material is assumed to have isotropic ferromagnetic properties in this research. The
The electronic structure of Yb implanted ZnO has been studied by the resonant photoemission spect... more The electronic structure of Yb implanted ZnO has been studied by the resonant photoemission spectroscopy (RPES). The contribution of Yb 4f partial density of states (PDOS) is predominant in the binding energy (BE) about 7.5 and ~11.7 eV below the VB maximum. At the resonance energy, around 182 eV, the multiplet structure with the highest BE shows the strongest resonance (around 11.7 eV) that corresponds to the 1 I multiplet which is almost exclusively responsible for this resonance, while 3 H and 3 F states are responsible for the resonance around 7.5 eV. It was also found that the Yb 4f PDOS distribution shows some similarity to Yb2O3.
The Preisach model formalism has been applied to analyse hysteresis measurement results for evalu... more The Preisach model formalism has been applied to analyse hysteresis measurement results for evaluating fatigue damage in Fe-C alloys caused by cyclic fatigue loading. Hysteresis loops and differential permeability curves were measured at various stages of the fatigue life of the samples. The parameters which were built by means of the PMF and the classical hysteresis magnetic parameters (such as
The influence of different heat treatments on the magnetic and magnetoelastic properties of highl... more The influence of different heat treatments on the magnetic and magnetoelastic properties of highly magnetostrictive CoFe 2 O 4 has been investigated. The first order cubic anisotropy coefficient, coercive field, magnetostriction and high strain sensitivity were observed to decrease as the heat treatment temperature increased. The saturation magnetization of the samples on the other hand increased with increase in heat treatment temperature. These changes were not accompanied by any observable changes in crystal structure or composition and are indicative of migration of Co 2 + from the octahedral sites (B-sites) to the tetrahedral sites (A-sites) and Fe 3 + from the A-sites to the B-sites of the spinel structure. Different distributions of the cations at the two distinct lattice sites can strongly affect the magnetic and magnetoelastic properties of these materials.
Differences in the microstructure and magnetic properties of highly magnetostrictive cobalt ferri... more Differences in the microstructure and magnetic properties of highly magnetostrictive cobalt ferrite resulting from the effects of different vacuum sintering temperatures and times have been investigated. A vacuum environment was chosen to allow direct comparison of results with air-sintered samples which are more often reported in the literature. It was found that vacuum sintering resulted in the development of a solid solution second phase with composition Co 1Àx Fe x O 4 (x$0.33). There was a decrease in magnetostriction as a result of the formation of the second phase. Furthermore, differences in sintering temperatures were found to have a greater effect on the magnetostriction than differences in sintering times. It was found that the first order cubic anisotropy coefficient initially increased with both sintering temperature and time, before peaking and decreasing to its lowest measured value. The lowest anisotropy was therefore achieved with samples sintered at higher temperatures and longer times.
Gd 5 (Si x Ge 1 À x) 4 , known for its giant magnetocaloric effect, also exhibits a colossal stra... more Gd 5 (Si x Ge 1 À x) 4 , known for its giant magnetocaloric effect, also exhibits a colossal strain of the order of 10,000 ppm for a single crystal near its coupled first-order magnetic-structural phase transition, which occurs near room temperature for the compositions 0.41 r x r 0.575. Such colossal strain can be utilised for both magnetic sensor and actuator applications. In this study, various measurements have been carried out on strain as a function of magnetic field strength and as a function of temperature on single crystal Gd 5 Si 2 Ge 2 (x ¼ 0.5), and polycrystalline Gd 5 Si 1.95 Ge 2.05 (x ¼ 0.487) and Gd 5 Si 2.09 Ge 1.91 (x ¼ 0.52). Additionally a giant magnetostriction/thermally induced strain of the order of 1800 ppm in polycrystalline Gd 5 Si 2.09 Ge 1.91 was observed at its first order phase transition on varying temperature using a Peltier cell without the use of bulky equipment such as cryostat or superconducting magnet.
We have investigated the magnetic properties of a Co 36 Fe 36 Si 4 B 20 Nb 4 alloy developed for ... more We have investigated the magnetic properties of a Co 36 Fe 36 Si 4 B 20 Nb 4 alloy developed for high temperature soft magnetic applications. Studies of the crystallization of the alloy, prepared in the form of amorphous ribbons by melt-spinning, were performed using differential scanning calorimetry and X-ray diffraction. These studies, and further validation by transmission electron microscopy, suggested the formation of ðCoFeÞ 2 Si nanoparticles dispersed in an amorphous matrix during the first stage of crystallization which occurred at around 845 K. The formation of this nanocrystalline state by annealing at temperatures between 825 and 875 K not only raised the Curie temperature of the material to above 1000 K but also gave superior soft magnetic properties with a coercivity less than 50 A/m (625 mOe). However, at higher annealing temperatures, formation of strongly anisotropic phases with out of plane domain magnetization, observed by magnetic force microscopy, resulted in deterioration of the soft magnetic properties.
Determination of Curie temperature by plotting magnetic moment vs. temperature curves requires a ... more Determination of Curie temperature by plotting magnetic moment vs. temperature curves requires a small applied field, which influences the measurement and temporarily disturbs the temperature of the sample especially for highly magnetocaloric materials. The Arrott plot technique was therefore used in order to determine the Curie temperature for a magnetocaloric Gd5Si2. 7Ge1. 3 (x= 0.675) single crystal sample. This technique was compared with other methods such as the inflection point technique and the line ...
ABSTRACT The Jiles-Atherton (JA) theory of hysteresis has been extended in the present paper to m... more ABSTRACT The Jiles-Atherton (JA) theory of hysteresis has been extended in the present paper to model hysteresis in two-phase magnetic materials. Two-phase materials are those that exhibit two magnetic phases in one hysteresis cycle: one at lower fields and the other at higher fields. In magnetic hysteresis, the transition from one phase to the other i.e. low field phase to high field phase depends mainly on the exchange field. Hence, the material-dependent microstructural parameters of JA theory: spontaneous magnetization, M S , pinning factor, k , domain density, a , domain coupling, alpha , and reversibility factor, c , are represented as functions of the exchange field. Several cases based on this model have been discussed and compared with the measured data from existing literature. The shapes of the calculated and measured hysteresis loops are in excellent agreement.
Computer simulations were used to investigate the performance of a microscale ferrofluid-based ma... more Computer simulations were used to investigate the performance of a microscale ferrofluid-based magnetic actuator developed for liquid dispensing in microfluidic channels. The actuation was based on the movement of a ferrofluid plug in a magnetic field gradient generated by on-chip effectively infinite parallel conductors. The movement, positioning, and retaining of ferrofluid plugs with different lengths at various locations along a microfluidic channel were investigated for two cases. In case (a), the magnetic field gradient was generated by a single conductor; when the ferrofluid reached its equilibrium position, the current was switched off and the nearest neighbor conductor was energized. A similar, consecutive on/off current switching was performed for case (b), where a set of conductors was energized simultaneously.
Gd 5 ͑Si x Ge 1−x ͒ 4 for 0.41ഛ x ഛ 0.5 is orthorhombic and ferromagnetic at lower temperature, m... more Gd 5 ͑Si x Ge 1−x ͒ 4 for 0.41ഛ x ഛ 0.5 is orthorhombic and ferromagnetic at lower temperature, monoclinic and paramagnetic at higher temperature, and shows a first order magnetic-structural phase transition between the two. Magnetic moment versus magnetic field ͑MH͒ isotherms were measured just above the first order transition temperature for Gd 5 Si 1.95 Ge 2.05 and Gd 5 Si 2 Ge 2 samples and the field-induced coupled phase transition from paramagnetic/monoclinic to ferromagnetic/ orthorhombic phase was observed. Using the method developed by Arrott ͓Phys. Rev. 108, 1394 ͑1957͔͒, the ferromagnetic portions of the MH isotherms were used to project the second order magnetic phase transition temperature of the orthorhombic phase, a region where the transition does not occur due to the first order transition at a lower temperature. These data points fall on the extrapolated line of the second order phase transition, drawn from the Si-rich region of the phase diagram.
ABSTRACT Abstract–$rm Gd\_5({rm Si\_rm xrm Ge\_1-rm x\})_4\$ exhibits a first order phase transit... more ABSTRACT Abstract–$rm Gd\_5({rm Si\_rm xrm Ge\_1-rm x\})_4\$ exhibits a first order phase transition for the compositions $0<rm x<0.575$ leading to a magnetic phase transition as well. It is not possible to measure the second order phase (magnetic) transition temperatures of the individual phases with direct measurements. This is because the first order phase transition occurs before the second order phase transition. With modified Arrott plots we have shown previously that it is possible to estimate the second order phase transition of the $rm Gd\_5rm Si\_4\$ -type orthorhombic phase. In this paper we have estimated the second order phase transition temperature of the $rm Gd\_5rm Si\_2rm Ge\_2\$-type monoclinic phase using a single crystal sample of $rm Gd\_5rm Si\_1.5rm Ge\_2.5\$ (0.375) which falls in the mixed phase region of the sample.
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Papers by Y. Melikhov