Carlos Garcia | Bogazici University (original) (raw)

Papers by Carlos Garcia

Sensors and Actuators B-Chemical, 2007

... [8] A. Zhukov, J. Gonzalez, JM Blanco, MJ Prieto, E. Pina and M. Vazquez, Induced magnetic an... more ... [8] A. Zhukov, J. Gonzalez, JM Blanco, MJ Prieto, E. Pina and M. Vazquez, Induced magnetic anisotropy in Co–Mn–Si–B amorphous microwires, J. Appl. Phys. 87 (2000), p. 1402. OJPS full text | Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (28). ...

We report an interesting case where magnetic phenomena can transcend mesoscopic scales. Our syste... more We report an interesting case where magnetic phenomena can transcend mesoscopic scales. Our system consists of tubes created by the assembly of dipolar spheres. The cylindrical topology results in the breakup of degeneracy observed in planar square and triangular packings. As far as the ground state is concerned, the tubes switch from circular to axial magnetization with increasing tube length. All magnetostatic properties found in magnetic nanotubes, in which the dipolar interaction is comparable to or dominant over the exchange interaction, are reproduced by the dipolar tubes including an intermediary helically magnetized state. Besides, we discuss the antiferromagnetic phase resulting from the square arrangement of the dipolar spheres and its interesting vortex state. † Electronic supplementary information (ESI) available. See

The total sputtering yield of 6 nm thick polycrystalline tantalum films resulting from H 2 + ion ... more The total sputtering yield of 6 nm thick polycrystalline tantalum films resulting from H 2 + ion bombardment, at normal incidence, has been determined. For this purpose, we study the evolution of the energy loss of protons transmitted through very thin films of tantalum following bombardment with controlled doses of H 2 + . The energy of the incident ions ranges from 3 to 11 keV. Our method allows us to determine how to find the limit of the thin film surface contamination which is important for stopping power measurements of pure samples. It also allows to prepare films of predetermined variable thickness.

This image illustrates the spontaneous self-assembly of magnetic nanoparticles into macroscopic c... more This image illustrates the spontaneous self-assembly of magnetic nanoparticles into macroscopic chains by using a combination of magnetron sputtering and gas aggregation techniques. This research, a DAFNEOX collaboration, studies the behaviour of complex agglomerates at the nano-and mesoscales. The low-kinetic energy of the particles inside the magnetron vacuum chamber and strong dipolar magnetic interaction between individual nanoparticles are responsible for particles' agglomeration at very low volume fractions. These results prove that the cluster gun technique can go beyond single particle fabrication into controlled and reproducible self-assembly of nanoparticles.

Devices based on soft ferromagnetic materials are promising for high-frequency flexible electroni... more Devices based on soft ferromagnetic materials are promising for high-frequency flexible electronics. Especially, wide-range tunable ferromagnetic resonance response of ferromagnetic microwires and ribbons can be functionalized in the form of magneto-impedance sensors in stretchable, bendable and twistable environments. A vector network analyzer calibrated by standard techniques is required to characterize the high-frequency properties of such devices. However, most of the calibration techniques necessitate calculations, computer simulations, and/or fabricating calibration kits in the shape of various test fixtures. Here, we employ a fixture calibration method for high-frequency (up to 4 GHz) impedance measurements of CoFeSiB microwires and melt-spun ribbons taking zero applied magnetic field as the reference. This method is based on a virtual de-embedding procedure, in which a reference signal is subtracted from all the subsequent measurements, which reduces the time for the total calibration procedure down to few minutes. Applications of the method are not limited to the cases where applied magnetic field varies. Any external parameter (strain, temperature, pressure etc.) that can change the impedance is allowed by this method. ⁎ Corresponding authors.

We present an alternative measurement technique for the longitudinal spin Seebeck effect (SSE), b... more We present an alternative measurement technique for the longitudinal spin Seebeck effect (SSE), based on harmonic analysis of the signal measured in the Y 3 Fe 5 O 12 =Pt bilayer. In our experimental setup, we use a harmonic magnetic field and a static thermal gradient in the longitudinal configuration to induce a square-wave SSE signal. By using a phase-sensitive detection technique (lock-in), we can reduce the impact of electrical noise, which improves sensitivity and, through harmonic analysis of the measured signal, decouples in real time the SSE signal from other thermoelectric effects.

In this work, we studied the magnetic properties of as-prepared and annealed Ni-Mn-Ga Heusler all... more In this work, we studied the magnetic properties of as-prepared and annealed Ni-Mn-Ga Heusler alloy glass-covered microwires. We observed that the annealing conditions strongly affect the magnetic field dependencies of magnetic moments, the temperature dependence of the magnetization, and the Curie temperature of microwires. By mixing the microwires annealed at different temperatures, we achieved the broadening of the second-order phase transition.

We present a variable variance Preisach model that fully accounts for the different magnetization... more We present a variable variance Preisach model that fully accounts for the different magnetization processes of a multilayer structure with perpendicular magnetic anisotropy by adjusting the evolution of the interaction variance as the magnetization changes. We successfully compare in a quantitative manner the results obtained with this model to experimental hysteresis loops of several [CoFeB/Pd] n multilayers. The effect of the number of repetitions and the thicknesses of the CoFeB and Pd layers on the magnetization reversal of the multilayer structure is studied, and it is found that many of the observed phenomena can be attributed to an increase of the magnetostatic interactions and subsequent decrease of the size of the magnetic domains. Increasing the CoFeB thickness leads to the disappearance of the perpendicular anisotropy, and such a minimum thickness of the Pd layer is necessary to achieve an out-of-plane magnetization.

The application of a static thermal gradient (∇ ∇ ∇T ) across the bilayer interface along the z−d... more The application of a static thermal gradient (∇ ∇ ∇T ) across the bilayer interface along the z−direction and an alternating magnetic field (H H H ext (t) = H 0 sin(ωt)), parallel to the sample plane along the ±x−direction (∇ ∇ ∇T ⊥ H H H ext ), generate an electromotive force (EMF) in the Pt layer along the y−direction. The equivalent circuit model for the Pt/YIG bilayer film utilized in this work is shown in (a). In this model, the Pt layer acts as an ac-voltage source composed of two ideal ac-voltage sources connected in series. The electrical resistance (R) of the Pt layer acts as a load resistor. V H is the voltage induced by the variation of the magnetic field flux through the circuit loop done by the Faraday's law of induction. V SSE is originated, via inverse spin Hall effect (ISHE), by the conversion of the spin current (produced by the SSE) and injected in the Pt layer from the YIG layer along the z−direction, into an electric field (E E E ISHE ).

A model describing the ferromagnetic resonance of multilayer structures is used to characterize t... more A model describing the ferromagnetic resonance of multilayer structures is used to characterize the interface anisotropy constant and interlayer exchange coupling strength associated to individual components of [CoFeB/Pd] n multilayers with perpendicular magnetic anisotropy and [CoFeB/Pd] 5 /(CoFeB or Co) exchange spring structures by comparing with ferromagnetic resonance behavior measurements. We find that the effective perpendicular anisotropy increases with the number of repetitions of the multilayer, which we could explain only after accounting for a different anisotropy at the bottom repetition of the multilayer with perpendicular anisotropy. Similarly, the characterization of the exchange coupling in our structures was only possible after accounting for individual components, thus portraying the importance of using a multilayer model to properly describe the magnetic behavior and properties of a multilayer structure. We find that the perpendicular anisotropy constant in amorphous Pd/CoFeB/Pd structures increases slightly from 0.295 to 0.315 mJ/m 2 when increasing the thickness of the CoFeB from 3 to 4Å. Furthermore, we find that the exchange coupling in CoFeB/Pd(10Å)/CoFeB structures decreases from 4.899 to 3.268 mJ/m 2 when increasing the thickness of the CoFeB from 3 to 4Å. Finally, we find that the magnitude of the anisotropy at Co/Pd interfaces is 65% larger than at CoFeB/Pd interfaces, and the exchange coupling at CoFeB/Pd/Co interfaces decreases approximately 30% when compared to a CoFeB/Pd/CoFeB structure.

Dynamic ferromagnetic resonance (FMR, X-band 9.8 GHz) and static first-order reversal curve (FORC... more Dynamic ferromagnetic resonance (FMR, X-band 9.8 GHz) and static first-order reversal curve (FORC) techniques are combined to study the intrinsic exchange-bias distribution via measurements of in-plane angular variation in (FeNi/IrMn)n multilayers. The angular dependence of the exchange bias field was qualitatively and quantitatively investigated using both methods, which are sensitive to different couplings between the ferromagnetic layers. We have used the analysis of the angular dependence of first-order reversal curve (AFORC) data, extracted from FORC curves measured from 0 up to 360 in 10 steps. In addition, its counterpart angular dependence of FMR (AFMR) measurements were carried out and correlated with the AFORC results.

An analytical study of the spectral line shape of ferromagnetic resonance (FMR) detected by spin ... more An analytical study of the spectral line shape of ferromagnetic resonance (FMR) detected by spin rectification effect and driven by the combined action of spin-transfer torque (STT) and voltage-controlled magnetic anisotropy (VCMA) is developed. The system under consideration consists of a magnetic tunnel junction (MTJ). Explicit expressions for the symmetric and asymmetric components of the rectified voltage are derived, where the role of the VCMA, in-plane STT, and field-like torque is clearly identified and discussed. Typical geometrical configurations are particularly analyzed and compared with recent experimental results. The analytical findings show that the change of sign in the FMR response upon reversal of the magnetization is completely due to VCMA. By distinguishing in-plane, out-of-plane, and full magnetization reversal processes, it is shown that the VCMA induces a change of sign in the symmetric part for the in-plane and out-of-plane magnetization reversal, while the asymmetric part change its sign under a full and in-plane reversion of the magnetization. Explicit expressions of the symmetric and asymmetric contributions of the spectral line shape allow us to detect under what conditions the STT and VCMA can increase or decrease the FMR spectral line shape. The proposed theory allows access to a better understanding of the physics behind ferromagnetic resonance phenomena, promoting potential applications in STT+VCMA-based MTJs.

A theoretical and experimental study of the influence of small offsets of the magnetic field (dH)... more A theoretical and experimental study of the influence of small offsets of the magnetic field (dH) on the measurement accuracy of the spectroscopic g-factor (g) and saturation magnetization (M s ) obtained by broadband ferromagnetic resonance (FMR) measurements is presented. The random nature of dH generates systematic and opposite sign deviations of the values of g and M s with respect to their true values. A dH on the order of a few Oe leads to a $10% error of g and M s for a typical range of frequencies employed in broadband FMR experiments. We propose a simple experimental methodology to significantly minimize the effect of dH on the fitted values of g and M s , eliminating their apparent dependence in the range of frequencies employed. Our method was successfully tested using broadband FMR measurements on a 5 nm thick Ni 80 Fe 20 film for frequencies ranging between 3 and 17 GHz. Published by AIP Publishing. https://doi.

The magnetic properties of radially oriented Co, Ni, and CoNi alloy nanowires synthesized by puls... more The magnetic properties of radially oriented Co, Ni, and CoNi alloy nanowires synthesized by pulsed electrodeposition into porous alumina structures are measured and compared with those of similar nanowires grown in a planar geometry. The alloy composition affects the anisotropy axis direction, which is determined by the balance between the magnetocrystalline and shape anisotropies, lying transverse to the nanowires for Co samples and along the nanowire axis for Ni. Monte Carlo simulations were performed to model the magnetic hysteresis of the radially oriented and planar geometry nanowires using an approach based on the conical distribution of anisotropies. The model provides an excellent fit compared with experimental hysteresis loops.

Rare-earth iron garnet thin films with perpendicular magnetic anisotropy (PMA) have recently attr... more Rare-earth iron garnet thin films with perpendicular magnetic anisotropy (PMA) have recently attracted a great deal of attention for spintronic applications. Thulium iron garnet (TmIG) has been successfully grown and TmIG/Pt heterostructures have been characterized. However, TmIG is not the only rare-earth iron garnet that can be grown with PMA. We report the growth, magnetic, and spintronic properties of epitaxial terbium iron garnet (TbIG) and europium iron garnet (EuIG) thin films with PMA. Reciprocal space mapping shows the films are lattice matched to the substrate without strain relaxation, even for films up to 56 nm thick. The lattice strain and magnetostriction coefficient produce PMA in certain cases. TbIG grows on (111) gadolinium gallium garnet (GGG) with PMA due to the in-plane compressive strain, whereas TbIG on (111) substituted GGG (SGGG) is in tension and has an in-plane easy axis. EuIG grows with PMA on and GGG substrates, which facilitates the investigation of spintronic properties as a function of orientation. Both garnets have excess rare earth, which is believed to occupy Fe octahedral sites and in the case of TbIG is associated with an increase in the compensation temperature to 330 K, higher than the bulk value. Anomalous Hall effect (AHE) measurements of Pt/EuIG Hall crosses show that the spin mixing conductance of Pt/ (111) and (100) EuIG is similar. AHE measurements of Pt/TbIG Hall crosses reveal a sign change in the AHE amplitude at the compensation point analogous to all-metallic systems.

The dependence of the asymmetric magnetoimpedance (MI) response on the directions of both the mag... more The dependence of the asymmetric magnetoimpedance (MI) response on the directions of both the magnetic field and the exchange bias is studied for an [Ni-Fe(60 nm)/Ir-Mn(35 nm)] × 5 multilayer system. The antiferromagnetic (AFM) layers create an exchange bias that shifts both the hysteresis loop and the MI response of Ni-Fe; the strength of this coupling depends on the thicknesses of both the ferromagnetic layer and the AFM layer. Tuning the exchange-bias angle and the applied-magnetic-field direction provides a practical method to control the symmetry and the magnitude of the MI response. The observed asymmetric response can be attributed to the coexistence of two anisotropies, the induced exchange-bias anisotropy and the magnetocrystalline anisotropy. Both are distinct components of the exchange-coupled Stoner-Wohlfarth energy density that forms a basis for simulations within the conventional Landau-Lifshitz-Gilbert framework. The model reproduces the main features of the experimental results, providing a deeper understanding of the effect of the anisotropy components on the MI characteristic curve and ratio. The results can be used for the development of an asymmetric MI exchange-biased thin-film element in an autobiased linear-magnetic-field sensor.

Sensors and Actuators B-Chemical, 2007

... [8] A. Zhukov, J. Gonzalez, JM Blanco, MJ Prieto, E. Pina and M. Vazquez, Induced magnetic an... more ... [8] A. Zhukov, J. Gonzalez, JM Blanco, MJ Prieto, E. Pina and M. Vazquez, Induced magnetic anisotropy in Co–Mn–Si–B amorphous microwires, J. Appl. Phys. 87 (2000), p. 1402. OJPS full text | Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (28). ...

We report an interesting case where magnetic phenomena can transcend mesoscopic scales. Our syste... more We report an interesting case where magnetic phenomena can transcend mesoscopic scales. Our system consists of tubes created by the assembly of dipolar spheres. The cylindrical topology results in the breakup of degeneracy observed in planar square and triangular packings. As far as the ground state is concerned, the tubes switch from circular to axial magnetization with increasing tube length. All magnetostatic properties found in magnetic nanotubes, in which the dipolar interaction is comparable to or dominant over the exchange interaction, are reproduced by the dipolar tubes including an intermediary helically magnetized state. Besides, we discuss the antiferromagnetic phase resulting from the square arrangement of the dipolar spheres and its interesting vortex state. † Electronic supplementary information (ESI) available. See

The total sputtering yield of 6 nm thick polycrystalline tantalum films resulting from H 2 + ion ... more The total sputtering yield of 6 nm thick polycrystalline tantalum films resulting from H 2 + ion bombardment, at normal incidence, has been determined. For this purpose, we study the evolution of the energy loss of protons transmitted through very thin films of tantalum following bombardment with controlled doses of H 2 + . The energy of the incident ions ranges from 3 to 11 keV. Our method allows us to determine how to find the limit of the thin film surface contamination which is important for stopping power measurements of pure samples. It also allows to prepare films of predetermined variable thickness.

This image illustrates the spontaneous self-assembly of magnetic nanoparticles into macroscopic c... more This image illustrates the spontaneous self-assembly of magnetic nanoparticles into macroscopic chains by using a combination of magnetron sputtering and gas aggregation techniques. This research, a DAFNEOX collaboration, studies the behaviour of complex agglomerates at the nano-and mesoscales. The low-kinetic energy of the particles inside the magnetron vacuum chamber and strong dipolar magnetic interaction between individual nanoparticles are responsible for particles' agglomeration at very low volume fractions. These results prove that the cluster gun technique can go beyond single particle fabrication into controlled and reproducible self-assembly of nanoparticles.

Devices based on soft ferromagnetic materials are promising for high-frequency flexible electroni... more Devices based on soft ferromagnetic materials are promising for high-frequency flexible electronics. Especially, wide-range tunable ferromagnetic resonance response of ferromagnetic microwires and ribbons can be functionalized in the form of magneto-impedance sensors in stretchable, bendable and twistable environments. A vector network analyzer calibrated by standard techniques is required to characterize the high-frequency properties of such devices. However, most of the calibration techniques necessitate calculations, computer simulations, and/or fabricating calibration kits in the shape of various test fixtures. Here, we employ a fixture calibration method for high-frequency (up to 4 GHz) impedance measurements of CoFeSiB microwires and melt-spun ribbons taking zero applied magnetic field as the reference. This method is based on a virtual de-embedding procedure, in which a reference signal is subtracted from all the subsequent measurements, which reduces the time for the total calibration procedure down to few minutes. Applications of the method are not limited to the cases where applied magnetic field varies. Any external parameter (strain, temperature, pressure etc.) that can change the impedance is allowed by this method. ⁎ Corresponding authors.

We present an alternative measurement technique for the longitudinal spin Seebeck effect (SSE), b... more We present an alternative measurement technique for the longitudinal spin Seebeck effect (SSE), based on harmonic analysis of the signal measured in the Y 3 Fe 5 O 12 =Pt bilayer. In our experimental setup, we use a harmonic magnetic field and a static thermal gradient in the longitudinal configuration to induce a square-wave SSE signal. By using a phase-sensitive detection technique (lock-in), we can reduce the impact of electrical noise, which improves sensitivity and, through harmonic analysis of the measured signal, decouples in real time the SSE signal from other thermoelectric effects.

In this work, we studied the magnetic properties of as-prepared and annealed Ni-Mn-Ga Heusler all... more In this work, we studied the magnetic properties of as-prepared and annealed Ni-Mn-Ga Heusler alloy glass-covered microwires. We observed that the annealing conditions strongly affect the magnetic field dependencies of magnetic moments, the temperature dependence of the magnetization, and the Curie temperature of microwires. By mixing the microwires annealed at different temperatures, we achieved the broadening of the second-order phase transition.

We present a variable variance Preisach model that fully accounts for the different magnetization... more We present a variable variance Preisach model that fully accounts for the different magnetization processes of a multilayer structure with perpendicular magnetic anisotropy by adjusting the evolution of the interaction variance as the magnetization changes. We successfully compare in a quantitative manner the results obtained with this model to experimental hysteresis loops of several [CoFeB/Pd] n multilayers. The effect of the number of repetitions and the thicknesses of the CoFeB and Pd layers on the magnetization reversal of the multilayer structure is studied, and it is found that many of the observed phenomena can be attributed to an increase of the magnetostatic interactions and subsequent decrease of the size of the magnetic domains. Increasing the CoFeB thickness leads to the disappearance of the perpendicular anisotropy, and such a minimum thickness of the Pd layer is necessary to achieve an out-of-plane magnetization.

The application of a static thermal gradient (∇ ∇ ∇T ) across the bilayer interface along the z−d... more The application of a static thermal gradient (∇ ∇ ∇T ) across the bilayer interface along the z−direction and an alternating magnetic field (H H H ext (t) = H 0 sin(ωt)), parallel to the sample plane along the ±x−direction (∇ ∇ ∇T ⊥ H H H ext ), generate an electromotive force (EMF) in the Pt layer along the y−direction. The equivalent circuit model for the Pt/YIG bilayer film utilized in this work is shown in (a). In this model, the Pt layer acts as an ac-voltage source composed of two ideal ac-voltage sources connected in series. The electrical resistance (R) of the Pt layer acts as a load resistor. V H is the voltage induced by the variation of the magnetic field flux through the circuit loop done by the Faraday's law of induction. V SSE is originated, via inverse spin Hall effect (ISHE), by the conversion of the spin current (produced by the SSE) and injected in the Pt layer from the YIG layer along the z−direction, into an electric field (E E E ISHE ).

A model describing the ferromagnetic resonance of multilayer structures is used to characterize t... more A model describing the ferromagnetic resonance of multilayer structures is used to characterize the interface anisotropy constant and interlayer exchange coupling strength associated to individual components of [CoFeB/Pd] n multilayers with perpendicular magnetic anisotropy and [CoFeB/Pd] 5 /(CoFeB or Co) exchange spring structures by comparing with ferromagnetic resonance behavior measurements. We find that the effective perpendicular anisotropy increases with the number of repetitions of the multilayer, which we could explain only after accounting for a different anisotropy at the bottom repetition of the multilayer with perpendicular anisotropy. Similarly, the characterization of the exchange coupling in our structures was only possible after accounting for individual components, thus portraying the importance of using a multilayer model to properly describe the magnetic behavior and properties of a multilayer structure. We find that the perpendicular anisotropy constant in amorphous Pd/CoFeB/Pd structures increases slightly from 0.295 to 0.315 mJ/m 2 when increasing the thickness of the CoFeB from 3 to 4Å. Furthermore, we find that the exchange coupling in CoFeB/Pd(10Å)/CoFeB structures decreases from 4.899 to 3.268 mJ/m 2 when increasing the thickness of the CoFeB from 3 to 4Å. Finally, we find that the magnitude of the anisotropy at Co/Pd interfaces is 65% larger than at CoFeB/Pd interfaces, and the exchange coupling at CoFeB/Pd/Co interfaces decreases approximately 30% when compared to a CoFeB/Pd/CoFeB structure.

Dynamic ferromagnetic resonance (FMR, X-band 9.8 GHz) and static first-order reversal curve (FORC... more Dynamic ferromagnetic resonance (FMR, X-band 9.8 GHz) and static first-order reversal curve (FORC) techniques are combined to study the intrinsic exchange-bias distribution via measurements of in-plane angular variation in (FeNi/IrMn)n multilayers. The angular dependence of the exchange bias field was qualitatively and quantitatively investigated using both methods, which are sensitive to different couplings between the ferromagnetic layers. We have used the analysis of the angular dependence of first-order reversal curve (AFORC) data, extracted from FORC curves measured from 0 up to 360 in 10 steps. In addition, its counterpart angular dependence of FMR (AFMR) measurements were carried out and correlated with the AFORC results.

An analytical study of the spectral line shape of ferromagnetic resonance (FMR) detected by spin ... more An analytical study of the spectral line shape of ferromagnetic resonance (FMR) detected by spin rectification effect and driven by the combined action of spin-transfer torque (STT) and voltage-controlled magnetic anisotropy (VCMA) is developed. The system under consideration consists of a magnetic tunnel junction (MTJ). Explicit expressions for the symmetric and asymmetric components of the rectified voltage are derived, where the role of the VCMA, in-plane STT, and field-like torque is clearly identified and discussed. Typical geometrical configurations are particularly analyzed and compared with recent experimental results. The analytical findings show that the change of sign in the FMR response upon reversal of the magnetization is completely due to VCMA. By distinguishing in-plane, out-of-plane, and full magnetization reversal processes, it is shown that the VCMA induces a change of sign in the symmetric part for the in-plane and out-of-plane magnetization reversal, while the asymmetric part change its sign under a full and in-plane reversion of the magnetization. Explicit expressions of the symmetric and asymmetric contributions of the spectral line shape allow us to detect under what conditions the STT and VCMA can increase or decrease the FMR spectral line shape. The proposed theory allows access to a better understanding of the physics behind ferromagnetic resonance phenomena, promoting potential applications in STT+VCMA-based MTJs.

A theoretical and experimental study of the influence of small offsets of the magnetic field (dH)... more A theoretical and experimental study of the influence of small offsets of the magnetic field (dH) on the measurement accuracy of the spectroscopic g-factor (g) and saturation magnetization (M s ) obtained by broadband ferromagnetic resonance (FMR) measurements is presented. The random nature of dH generates systematic and opposite sign deviations of the values of g and M s with respect to their true values. A dH on the order of a few Oe leads to a $10% error of g and M s for a typical range of frequencies employed in broadband FMR experiments. We propose a simple experimental methodology to significantly minimize the effect of dH on the fitted values of g and M s , eliminating their apparent dependence in the range of frequencies employed. Our method was successfully tested using broadband FMR measurements on a 5 nm thick Ni 80 Fe 20 film for frequencies ranging between 3 and 17 GHz. Published by AIP Publishing. https://doi.

The magnetic properties of radially oriented Co, Ni, and CoNi alloy nanowires synthesized by puls... more The magnetic properties of radially oriented Co, Ni, and CoNi alloy nanowires synthesized by pulsed electrodeposition into porous alumina structures are measured and compared with those of similar nanowires grown in a planar geometry. The alloy composition affects the anisotropy axis direction, which is determined by the balance between the magnetocrystalline and shape anisotropies, lying transverse to the nanowires for Co samples and along the nanowire axis for Ni. Monte Carlo simulations were performed to model the magnetic hysteresis of the radially oriented and planar geometry nanowires using an approach based on the conical distribution of anisotropies. The model provides an excellent fit compared with experimental hysteresis loops.

Rare-earth iron garnet thin films with perpendicular magnetic anisotropy (PMA) have recently attr... more Rare-earth iron garnet thin films with perpendicular magnetic anisotropy (PMA) have recently attracted a great deal of attention for spintronic applications. Thulium iron garnet (TmIG) has been successfully grown and TmIG/Pt heterostructures have been characterized. However, TmIG is not the only rare-earth iron garnet that can be grown with PMA. We report the growth, magnetic, and spintronic properties of epitaxial terbium iron garnet (TbIG) and europium iron garnet (EuIG) thin films with PMA. Reciprocal space mapping shows the films are lattice matched to the substrate without strain relaxation, even for films up to 56 nm thick. The lattice strain and magnetostriction coefficient produce PMA in certain cases. TbIG grows on (111) gadolinium gallium garnet (GGG) with PMA due to the in-plane compressive strain, whereas TbIG on (111) substituted GGG (SGGG) is in tension and has an in-plane easy axis. EuIG grows with PMA on and GGG substrates, which facilitates the investigation of spintronic properties as a function of orientation. Both garnets have excess rare earth, which is believed to occupy Fe octahedral sites and in the case of TbIG is associated with an increase in the compensation temperature to 330 K, higher than the bulk value. Anomalous Hall effect (AHE) measurements of Pt/EuIG Hall crosses show that the spin mixing conductance of Pt/ (111) and (100) EuIG is similar. AHE measurements of Pt/TbIG Hall crosses reveal a sign change in the AHE amplitude at the compensation point analogous to all-metallic systems.

The dependence of the asymmetric magnetoimpedance (MI) response on the directions of both the mag... more The dependence of the asymmetric magnetoimpedance (MI) response on the directions of both the magnetic field and the exchange bias is studied for an [Ni-Fe(60 nm)/Ir-Mn(35 nm)] × 5 multilayer system. The antiferromagnetic (AFM) layers create an exchange bias that shifts both the hysteresis loop and the MI response of Ni-Fe; the strength of this coupling depends on the thicknesses of both the ferromagnetic layer and the AFM layer. Tuning the exchange-bias angle and the applied-magnetic-field direction provides a practical method to control the symmetry and the magnitude of the MI response. The observed asymmetric response can be attributed to the coexistence of two anisotropies, the induced exchange-bias anisotropy and the magnetocrystalline anisotropy. Both are distinct components of the exchange-coupled Stoner-Wohlfarth energy density that forms a basis for simulations within the conventional Landau-Lifshitz-Gilbert framework. The model reproduces the main features of the experimental results, providing a deeper understanding of the effect of the anisotropy components on the MI characteristic curve and ratio. The results can be used for the development of an asymmetric MI exchange-biased thin-film element in an autobiased linear-magnetic-field sensor.