Publisher：Scientific Reports  

Understanding and manipulating the dynamic properties of the magnetic vortices stabilized in patterned ferromagnetic structures are of great interest owing to the superior resonant features with the high thermal stability and their flexible tunability. So far, numerous methods for investigating the dynamic properties of the magnetic vortex have been proposed and demonstrated. However, those techniques have some regulations such as spatial resolution, experimental facility and sensitivity. Here, we develop a simple and sensitive method for investigating the vortex-core dynamics by using the electrically separated excitation and detection circuits. We demonstrate that the resonant oscillation of the magnetic vortex induced by the amplitude-modulated alternating-sign magnetic field is efficiently picked up by the lock-in detection with the modulated frequency. By extending this method, we also investigate the size dependence and the influence of the magneto-static interaction in the resonant property of the magnetic vortex.

DOI： 10.1038/srep17922

Scopus

Publisher：IEEE Transactions on Magnetics  

A sensitive and reliable detection method for magnetic vortex core dynamics at the remanent state has been demonstrated. Perfectly symmetric potential created in a circular-shaped disk produces twofold symmetry in the position dependence of the resistance of the ferromagnetic disk. We find that the detectable second-harmonic voltage can be induced by flowing the dc current when the circular-shaped core oscillation is excited by the microwave magnetic field. The consistent features have been observed in the current dependence and field dependence of the signals, indicating that the present method is a powerful technique to characterize the core dynamics, even at the remanent state.

DOI： 10.1109/TMAG.2015.2435024

Scopus

Publisher：2015 IEEE International Magnetics Conference, INTERMAG 2015  

Dynamical spin injection is attractive mean for generating and controlling the spin current without the use of the electricity. So far, the mechanism of the dynamical spin injection is attributed to the spin pumping induced by the ferromagnetic resonance (FMR). Although its quantitative evaluation is not simple because of the coexistence of the dc and ac spin pumping currents, the experimental results related to the spin pumping are mainly analyzed only by focusing on the dc spin current. Since the magnitude of the ac spin current is much larger than that of the dc spin current, the consideration of the ac spin current may be important. Apart from the spin pumping, another driving mechanism for the dynamical spin injection, we are interested in the heating effect during the resonant precession. When the temperature gradient exists across the ferromagnet/ nonmagnet interface, the spin current is generated through the thermal spin injection (spin-dependent Seebeck effect)[1,2]. In this presentation, we develop the evaluation method of the FMR heating effect for the micro- or nano-sized ferromagnet and investigate the influence of the dynamical spin injection on the magnetization dynamics.

DOI： 10.1109/INTMAG.2015.7156977

Scopus

Publisher：2015 IEEE International Magnetics Conference, INTERMAG 2015  

Magnetic vortex is one of the interesting topic for the spin dynamics due to its attractive characteristic such as the high thermal stability and the small frequency dispersion. Most of studies on the magnetic vortex have been carried out by using circular-shaped ferromagnetic disk. So far, we have investigated the magnetic vortex confined in a triangular ferromagnetic dot and found some feature shown on triangular ferromagnetic dot such as the chirality of the vortex in the regular triangle can be controlled by the direction of the initialized in-plane magnetic field [1] and the resonant frequency of the vortex-core gyration motion in the triangular dot is higher than the circular one. In addition, we here report that the dynamics properties of vortex core is reconfigurable in a polygonal ferromagnetic dot due to its anisotropic shape.

DOI： 10.1109/INTMAG.2015.7156914

Scopus

Publisher：2015 IEEE International Magnetics Conference, INTERMAG 2015  

Metal-insulator transition (MIT) induced by the electric field has been intensively investigated owing to its potential for nano-sized resistance switching devices in the next generation as well as its simple device structure. Although the MIT has been reported in various oxides such as Mn oxide1), Gd oxide2), and Co-doped Ti oxide3), the microscopic origin of the phase transition is still controversial issue. It should be noted that some of the oxides showing the MIT include magnetic components, implying that the MIT is related to the transition of the spin state. To explore the correlation between the MIT and spin configuration, in the present study, we investigate the influence of the ferromagnetic electrode on the MIT.

DOI： 10.1109/INTMAG.2015.7157166

Scopus

Publisher：2015 IEEE International Magnetics Conference, INTERMAG 2015  

Resistive switching device consisting of metallic oxide layer sandwiched by the metallic electrodes has paid considerable attention to next-generation nano-electronic devices. Two major mechanisms; filament-type and interface-type, are known for the transition between the low-resistive and high-resistive states. In both mechanism, the low voltage operation is the common issue for the reliable and low-power consumption operations. From this view point, the devices, in general, consist of vertical stuck structure with the thin oxide layer. If one obtains the resistive switching operation in the laterally configured structure, we may obtain more flexible and functional device. It also should be noted that most of the metallic oxides showing the resistive switching include magnetic components1∼3). This implies that the resistance switching is related to the spin configuration in the metallic oxide. For these purpose, in the present study, we develop a novel method for the fabrication of the switching devices in lateral configuration and investigate the influence of the ferromagnetic electrode and spin orientation on the switching property.

DOI： 10.1109/INTMAG.2015.7156918

Scopus

Publisher：2015 IEEE International Magnetics Conference, INTERMAG 2015  

The resonant precession of the magnetizations such as the ferromagnetic resonance (FMR) and spin wave (SW) excitation is unique and attractive property of the ferromagnetic thin film for future applications in nano-electric and telecommunication devices. Especially, after establishing the concept of the spin current, the considerable attention has been paid to such spin dynamics. Moreover, the oscillation amplitude in such resonant spin motion is found to show the nonlinear responses under the high power excitation. These fascinating properties may open novel functional spintronic devices such as spin current amplifier and neuromophic operation. However, experimental difficulties and complicated spatial spin distribution make it difficult to understand the related phenomena deeply. In this presentation, we show that nonlinear responses for the FMR and the surface SW in a Permalloy strip can be simply excited by the application of non-uniform RF magnetic field with high amplitude.

DOI： 10.1109/INTMAG.2015.7156973

Scopus

Language：English  

Publisher：Scientific Reports  

A magnetic vortex structure stabilized in a micron or nano-sized ferromagnetic disk has a strong potential as a unit cell for spin-based nano-electronic devices because of negligible magnetostatic interaction and superior thermal stability. Moreover, various intriguing fundamental physics such as bloch point reversal and symmetry breaking can be induced in the dynamical behaviors in the magnetic vortex. The static and dynamic properties of the magnetic vortex can be tuned by the disk dimension and/or the separation distance between the disks. However, to realize these modifications, the preparations of other devices with different sample geometries are required. Here, we experimentally demonstrate that, in a regular-triangle Permalloy dot, the dynamic properties of a magnetic vortex are greatly modified by the application of the in-plane magnetic field. The obtained wide range tunability based on the asymmetric position dependence of the core potential provides attractive performances in the microwave spintronic devices.

DOI： 10.1038/srep03567

Scopus

Publisher：Journal of the Korean Physical Society  

The ferromagnetic resonance of a single micron-scale dot of permalloy was measured by using a vector network analyzer. The resonant frequency shifted to higher frequency with increasing aspect ratio of the sample. This tendency was remarkable for narrower width samples, especially the 1-μm-width dots. This means that the demagnetization effect of thin films for the ferromagnetic resonance becomes large when the sample width is less than 1 μm. The resonant frequency can be largely controlled by changing the sample width for a thin film with a width of less than 1 μm, which is a favorable characteristics for various microwave applications. © 2013 The Korean Physical Society.

DOI： 10.3938/jkps.63.800

Scopus

Publisher：Japanese Journal of Applied Physics  

Spin wave excitation and propagation properties in a permalloy were investigated using a vector network analyzer for the magnetostatic surface wave (MSSW) and magnetostatic backward volume wave (MSBVW) configurations. In the MSSW configuration, the excitation and transmission spectra show many peaks. They originate at the distance of antenna lines of the coplanar waveguide, and the waveguide design is important for selecting the excitation and transmission wave vectors of the spin wave. The attenuation length of the MSSW was estimated to be 7.1 μm, and the group velocity of the MSSW with a wave number of 0.26 μm-1 was estimated to be about 8.6 μm/ns for an external magnetic field of 20 mT. In the MSBVW configuration, however, the excitation spin wave spectrum shows a single peak, since many quantized peaks overlap. A transmission signal with a single peak was also detected, but this could be an artifact such as an induced current. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.083001

Scopus

Publisher：Japanese Journal of Applied Physics  

We investigated the size effect on ferromagnetic resonance (FMR) in a submicron-wide single permalloy bar. The resonant frequency markedly increased with decreasing bar width to less than 1 m, since the demagnetizing field is effectively modified by changing the bar width even in thin films. The resonant frequency difference between 100- and 1000-nm-wide bars was over 4 GHz in the absence of a magnetic field. This characteristic is promising for practical microwave devices because the desired resonant frequency can be obtained simply by varying the width of narrow ferromagnetic bars so that it is not necessary to change the material or magnetic field. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.053001

Scopus

Publisher：Applied Physics Letters  

A magnetic resonator consisting of periodical nonmagnetic electrodes on a ferromagnetic metallic film has been fabricated. We demonstrated that the resonator efficiently excites the standing magneto-static surface spin wave with the specific wavelength, which can be controlled by the interval of the periodical electrode. The operation frequency over 5 GHz was confirmed at the interval of 4 μ m under a small bias magnetic field less than 100 Oe. The optimization of the electrode pattern for the efficient detection of the standing spin wave was also demonstrated. © 2012 American Institute of Physics.

DOI： 10.1063/1.4766918

Scopus

Publisher：IEEE Transactions on Magnetics  

The static and dynamic magnetization properties in an exchange-coupled NiFe/FeMn/Cu trilayer system have been investigated. Although a clear loop shift was observed in the magnetization versus field curve, the magnitude of the exchange bias does not show a systematic dependence on the Cu thickness. On the other hand, from the ferromagnetic resonance measurements, the exchange bias is found to increase with increasing the Cu thickness. This result indicates that the resonant frequency can be controlled by the Cu thickness. The correlation between the coercivity and the damping constant is also discussed. © 2012 IEEE.

DOI： 10.1109/TMAG.2012.2201925

Scopus

Publisher：IEEE Transactions on Magnetics  

The magnetization dynamics of a pair of the magneto-statically coupled spin torque nano oscillators (STNOs) have been investigated by using the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation with a macro-spin approximation. First, we simulated the deterministic dynamics of the coupled STNOs. Numerical simulations show that the dipole coupling mediates in-phase or out-of-phase synchronization states in the pair of the STNOs. Moreover, we found that a bistable state consisting of both in-phase and out-of phase synchronization states can exist by adjusting the experimental parameters. Second, we simulated the stochastic dynamics of the coupled STNOs under common noisy current injection. It is found that the noisy current injection into the STNOs induces to chastic state transition from the out-of-phase synchronization state to the in-phase. Such state transition arises from the cooperative effects between the noise-induced synchronization and the magneto static interactions. © 2012 IEEE.

DOI： 10.1109/TMAG.2012.2201145

Scopus

Publisher：Journal of Applied Physics  

We have studied the magnetic domain structures in a magneto-statically- coupled chain array of the triangle dots and an isosceles triangle dot by means of magnetic force microscopy (MFM). Despite the strong magneto-static interaction in the chain array of the dots, each triangle dot takes a single vortex structure. The chirality of each dot is found to behave similarly to that for the isolated triangle dot. We also demonstrated that single-vortex and double-vortex structures with the desired chiralities can be stabilized in an isosceles triangle dot. © 2012 American Institute of Physics.

DOI： 10.1063/1.3673349

Scopus

Publisher：Journal of Applied Physics  

We have numerically studied the stochastic magnetization dynamics of a pair of spin torque nano oscillators (STNOs) under noisy current injection by using the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation with a macro-spin approximation. Common noisy current injection into both STNOs is found to induce the phase synchronizations, where two STNOs show in-phase or anti-phase locked precession depending on the sequences of Gaussian white noise. The noise-induced synchronization could be a possible application for controlling the output power in the array of the STNOs. © 2012 American Institute of Physics.

DOI： 10.1063/1.3680537

Scopus

Language：English  

Language：English  

Language：English  

Language：English  

Language：English  

Language：English  

Language：English  

Language：English  

Language：English  

Language：English  

Publisher：Applied Physics Letters  

We have proposed a method for controlling the vortex chirality in a squared permalloy dot by using the circular Oersted field locally induced by flowing a DC current across a small Py/Cu junctions. The reliability of the chirality control has been evaluated by measuring the nonlocal spin valve signal. The desired vortex chirality has been obtained when the injecting DC current has a moderate magnitude. However, the large DC current is found to reduce the control reliability. Another possibility for controlling the vortex structure using the large DC current injection was also discussed. © 2011 American Institute of Physics.

DOI： 10.1063/1.3669410

Scopus

Publisher：IEEE Transactions on Magnetics  

We report a large enhancement of spin-torque diode sensitivity in CoFeB/MgO/CoFeB magnetic tunnel junctions measured under perpendicular magnetic fields and dc bias currents. In the measurement of homodyne detection, a large dc output voltage of 190 μ V was obtained when an RF signal power of -30 dB·m and a dc current of +1.0 mA were applied. This value corresponds to the diode sensitivity of 190 mV/mW (260 mV/mW after impedance matching correction). The main origin of this enhancement is an offset of the damping torque and an increase in the precession angle induced by the spin-transfer torque due to the dc bias current application. © 2011 IEEE.

DOI： 10.1109/TMAG.2011.2159830

Scopus

Publisher：IEEE Transactions on Magnetics  

We have investigated the magneto- and spin-current-transport properties in patterned Gd wires in order to understand the interplay between the spin current and the spin entropy. From the magneto-transport measurements, the electrical resistance was found to decrease with decreasing the spin entropy because of the suppression of the spin fluctuation. We also found that the Gd acts as a strong absorber both for the ac and dc pure spin currents from the ferromagnetic resonance and nonlocal spin injection experiments. © 2011 IEEE.

DOI： 10.1109/TMAG.2011.2158407

Scopus

Publisher：IEEE Transactions on Magnetics  

Static and dynamical properties of a magnetic vortex stabilized in a regular polygonal nanomagnet were investigated. We have demonstrated that the chirality of the magnetic vortex in a odd-sided regular nanomagnet can be controlled by the in-plane magnetic field. We also observed the resonant spectrum of a vortex core in the triangular nanomagnet using the homodyne detection technique. The resonant frequency of the vortex core in the triangular nanomagnet was found to be higher than that in a circular nanomagnet. © 2011 IEEE.

DOI： 10.1109/TMAG.2011.2158408

Scopus

Language：English  

Language：Japanese  

Language：English  

Language：English  

Language：English  

Publisher：IEEE Region 10 Annual International Conference, Proceedings/TENCON  

We have proposed a method for controlling the vortex chirality in a regular polygonal nanomagnet with an odd number of sides using an in-plane magnetic field. We confirmed the reliability of the proposed method in the triangle, pentagonal and heptagonal nanomagnets by using micromagnetic simulation. However, when the number of the sides is 9 or more, the chirality does not change systematically because of the insufficient in-plane shape anisotropy. Stabilizations of a single vortex in polygonal nanomagnets with an even number of sides have been also investigated. ©2010 IEEE.

DOI： 10.1109/TENCON.2010.5686386

Scopus

Publisher：IEEE Region 10 Annual International Conference, Proceedings/TENCON  

We have investigated the cleaning condition of the Permalloy (Py) surface optimized for the efficient pure spin current injection in Py/Cu lateral spin valve structure. The efficiency of the spin injection is found to depend on the beam voltage and milling time strongly. The post annealing is also found to improve the spin injection efficiency. ©2010 IEEE.

DOI： 10.1109/TENCON.2010.5685852

Scopus

Publisher：Applied Physics Letters  

The authors have proposed a control method of the magnetic vortex chirality in regular polygonal nanomagnets with an odd number of sides. The asymmetric nucleation energy of the vortex from the uniformly magnetized state enables us to simply control the vortex chirality by an in-plane magnetic field. The reliability of the proposed method has been numerically and experimentally confirmed in the triangle, pentagonal, heptagonal, and nonagonal Permalloy nanomagnets. The authors also confirmed that the vortex chirality is uncontrollable when the number of the side is even. © 2010 American Institute of Physics.

DOI： 10.1063/1.3521407

Scopus

Publisher：Applied Physics Express  

We report on rf current-induced excitation of the ferromagnetic resonance in CoFeB/MgO/CoFeB magnetic tunnel junctions under a perpendicular magnetic field. By choosing an appropriate external field and using an Fe-rich CoFeB free layer, the effective precession of the free layer could be excited. In a measurement of homodyne detection, a large dc output voltage of 180 μV was obtained when an rf signal power of -25 dBm was applied. The sensitivity of this junction, as an rf rectifier, reaches about 170mV/mW (280mV/mW after impedance matching correction), which is the same order compared with that of a Schottky diode operated at room temperature. © 2010 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.3.073001

Scopus

Publisher：IEEE Transactions on Magnetics  

Very high thermal stability Δ0 was demonstrated in MgO-based magnetic tunnel junctions (MTJs) with CoFeB/Ru/CoFeB ferromagnetically coupled synthetic free layers (F-coupled Sy). Samples had a structure of underlayer/PtMn(15)/CoFe(2.5)/Ru(0.85)/CoFeB(3)/MgO(1)/F-coupled Sy/Ta(5)/Ru(7), where F-coupled Sy was CoFeB(2)/Ru(1.5)/CoFeB(dCoFeB=1-4 (nm unit). The MTJs were elliptical with approximate dimensions of 60 nm × 170 nm. Resistance-field (R-H) loops were measured repeatedly; the H-dependence of switching probability PSW was observed. From the distribution of switching field HC, thermal stability factor Δ0 was evaluated based on the Sharrock equation. The Δ0 values increased concomitantly with increasing thickness of the upper CoFeB layer dCoFeB. We obtained very large Δ0 values of about 248 when dCoFeB=4 nm. Such a large Δ0 originates in enhanced shape magnetic anisotropy in the F-coupled Sy. The shape anisotropy is lost because of the low effective magnetization if the magnetizations are coupled antiferromagnetically. The F-coupled Sy with a thicker upper magnetic layer is suitable for use in nonvolatile memory cells in magnetoresistive random access memory. © 2006 IEEE.

DOI： 10.1109/TMAG.2010.2045741

Scopus

Language：English  

Language：English  

Language：English  

Language：English  

Language：English  

Publisher：Applied Physics Letters  

We prepared MgO-based magnetic tunnel junctions having a CoFeB/Ru/CoFeB synthetic free layer in which magnetizations of the CoFeB layers were ferromagnetically coupled (F-coupled Sy) or antiferromagnetically coupled (AF-coupled Sy). We studied spin-transfer switchings to evaluate their thermal stability (Δ0 =K V/ kB T) and intrinsic switching current density (J C0). Although the free layers of two types showed nearly equal JC0, the Δ0 of F-coupled Sy was observed to be twice that of AF-coupled Sy. This difference is attributable to the shape magnetic anisotropy of the free-layer cells. Results show that F-coupled Sy is superior to AF-coupled Sy for memory applications. © 2009 American Institute of Physics.

DOI： 10.1063/1.3275753

Scopus

Publisher：Physical Review B - Condensed Matter and Materials Physics  

We experimentally investigated current-driven oscillation in fully epitaxial Fe(001)/MgO(001)/Fe(001) magnetic tunnel junctions (MTJs) to pave the way for a better understanding of why the linewidth (a few hundred MHz) of microwave oscillation in spin-torque nano-oscillators (STNOs) based on textured MTJs is much larger than that (smaller than 10 MHz) in STNOs based on current-perpendicular-to-plane giant-magnetoresistance junctions. The epitaxial Fe/MgO/Fe STNO is a model system for studying the physics of spin-transfer torque because it has a well-defined single-crystal barrier and electrode layers with atomically flat interfaces. In the Fe/MgO/Fe STNOs, clear spin-torque-induced switching and spin-torque-induced precession were observed in epitaxial MTJs. When the initial magnetic alignment was antiparallel and the bias current exceeded the threshold current, a state in which the spin-torque compensates for the damping, the STNOs showed a rapid increase in the peak intensity, a redshift of the peak frequency, and a minimum linewidth, all clear evidence of spin-torque-induced precession above the threshold current. The minimum linewidth of the STNOs was 200 MHz, which is comparable to that of textured CoFeB/MgO/CoFeB MTJs. This indicates that the origin of the large linewidth cannot be attributed to structural inhomogeneity in textured MTJs. When the initial magnetic alignment was parallel, the microwave spectrum showed a single peak, which has rarely been observed in textured MTJs without application of a perpendicular magnetic field. The mechanism of the single-peak oscillation can be explained by taking account of the induced perpendicular magnetic anisotropy in the 3-nm-thick Fe(001) free layer grown on the MgO(001) barrier layer. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevB.80.174405

Scopus

Publisher：Journal of Applied Physics  

We investigated the spin-torque diode effect in submicron-scale Co60 Fe20 B20 MgO (Cox Fe1-x)80 B20 (0≤x≤0.9) magnetic tunnel junctions (MTJs) under perpendicular magnetic fields Hext up to 10 kOe. A single peak was clearly observed in every spin-torque diode spectrum and the dependence of resonant frequency fres on Hext was well explained by using Kittel's formula. It was found that effective demagnetizing fields in the perpendicular-to-plane direction of the Fe-rich CoFeB free layers obtained from the spectra were considerably smaller than those expected from the magnetizations of the free layers. This suggested that the Fe-rich CoFeB free layers exhibited a perpendicular magnetic anisotropy, which agreed well with the reduced switching current density in the MTJs. © 2009 American Institute of Physics.

DOI： 10.1063/1.3057974

Scopus

Publisher：Journal of Applied Physics  

Magnetic properties, magnetoresistance (MR), and spin-transfer switching of magnetic tunnel junctions having a structure of Co60 Fe20 B20 3 nm/MgO 1 nm/ (Co75 Fe25) 80-X Cr (V) X B20 2 nm (X=0-25) were investigated. Magnetization of the (Co-Fe)-(Cr, V)-B free layer decreased from 1.2 T before substitution to 0.6 T at Cr of 10% (0.8 T at V of 10%). The MR ratio and a resistance-area product (RA) before substitution were, respectively, about 130% and about 2 μ m2. The MR ratio decreased to 80% at Cr of 10% and 40% at V of 10%. The RA values were almost independent of the composition. The intrinsic switching current density (Jc0) decreased from 15 to 8 MA/ cm2 at Cr of 10% and 12 MA/ cm2 for V of 10%. Upon the further increase in Cr and V, stable switching was difficult to observe. In summary, Jc0 decreased to half in the case of Cr, but the effect was small for V. © 2009 American Institute of Physics.

DOI： 10.1063/1.3068484

Scopus

Language：English  

Language：English  

Language：English  

Language：English  

Publisher：IEEE Transactions on Magnetics  

The line width of the ferromagnetic resonance (FMR) spectrum of Cu/CoFeB/Cu/Co/Cu is studied. Analyzing the FMR spectrum by the theory of spin pumping, we determined the penetration depth of the transverse spin current in the Co layer. The obtained penetration depth of Co is 1.7 nm. © 2008 IEEE.

DOI： 10.1109/TMAG.2008.2003036

Scopus

Publisher：IEEE Transactions on Magnetics  

The line width of the ferromagnetic resonance (FMR) spectrum of Cu/CoFeB/Cu/Co/Cu is studied. Analyzing the FMR spectrum by the theory of spin pumping, we determined the penetration depth of the transverse spin current in the Co layer. The obtained penetration depth of Co is 1.7 nm. © 2008 IEEE.

DOI： 10.1109/TMAG.2008.2003036

Scopus

Publisher：Applied Physics Express  

Spin pumping in nonmagnetic/ferromagnetic metal multilayers Is studied both theoretically and experimentally. We show that the line widths of the ferromagnetic resonance (FMR) spectrum depend on the thickness of the ferromagnetic metal layers, which must not be in resonance with the oscillating magnetic field. We also show that the penetration depths of the transverse spin current in ferromagnetic metals can be determined by analyzing the line widths of their FMR spectra. The obtained penetration depths in NiFe, CoFe, and CoFeB were 3.7, 2.5, and 12.0 nm, respectively. © 2008 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.1.031302

Scopus

Publisher：Journal of Applied Physics  

Co2FeSi films were prepared using magnetron sputtering technique on Cr buffer layers and MgO(001) substrates at various annealing temperatures. We investigated the crystal structures, magnetic properties (Ms and Hc), surface roughness, and magnetic damping constants (α) of the prepared Co2 FeSi films. Out-of-plane angular dependences of the resonance field and the linewidth of the ferromagnetic resonance spectra were measured and fitted using the Landau-Lifshitz-Gilbert equation to determine the damping constant. The as-deposited Co2 FeSi film exhibited an amorphous and disordered structure; the α value was 0.008. In contrast, the Co2 FeSi films annealed over 300 °C showed epitaxial growth and had a (001)-oriented and L 21 ordered structure. Both disordered and L 21 ordered Co2 FeSi films showed similar α values. © 2007 American Institute of Physics.

DOI： 10.1063/1.2709751

Scopus

Publisher：Journal of Magnetism and Magnetic Materials  

DC voltage generated in ferromagnetic resonance was investigated for Cu / F (20 nm) / Cu (F = Ni80 Fe20, Co) films. Microwave frequency was varied from 6 to 18 GHz and DC voltage depended significantly on the film shape and frequency. DC voltage for the circular patch films was enhanced remarkably at around 9 GHz. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.827

Scopus

Publisher：Physica Status Solidi (C) Current Topics in Solid State Physics  

In-plane magnetic anisotropy of a (Ga,Mn)As film has been investigated by measuring anisotropic magnetoresistance as a function of the direction of in-plane magnetic fields. Two Hall bars with channel direction [-110] or [100] were fabricated to detect the in-plane magnetization reversal process from both the longitudinal and the transverse components of anisotropic magnetoresistance. The results show the coexistence of cubic <100> easy axes and uniaxial [100] hard axis. The data are fitted well by a coherent magnetization model. Temperature dependence of the in-plane anisotropic fields, determined both by the magnetotransport measurements and by ferromagnetic resonance, is presented. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.

DOI： 10.1002/pssc.200672877

Scopus

Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers  

We determined the Gilbert damping constants of Fe-Co-. Ni and Co-Fe-B alloys with various compositions and half-metallic Co2MnAl Heusler alloy films prepared by magnetron sputtering. The ferromagnetic resonance (FMR) technique was used to determine the damping constants of the prepared films. The out-of-plane angular dependences of the resonance field (HR) and line width (ΔHpp) of FMR spectra were measured and fitted using the Landau-Lifshitz-Gilbert (LLG) equation. The experimental results fitted well, considering the inhomogeneities of the films in the fitting. The damping constants of the metallic films were much larger than those of bulk ferrimagnetic insulators and were roughly proportional to (g - 2)2, where g is the Lande g factor. We discuss the origin of magnetic damping, considering spin-orbit and s-d interactions. © 2006 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.45.3889

Scopus

Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers  

Ferromagnetic resonance (FMR) was measured in Cu/Ni80Fe 20/normal-metal: NM (d)/Pt, Cu/Ni80Fe20/NM (d) films with various d values to clarify the temperature dependence of spin-diffusion length induced by the precession of magnetization on Gilbert damping. The films were fabricated by rf magnetron sputtering. The out-of-plane angular dependences of FMR resonance field and linewidth were analyzed using a Landau-Lifshitz-Gilbert equation, and the Gilbert damping parameter G of NiFe was obtained. The obtained spin-diffusion lengths λSD were 350 and 950 nm at 300 and 4.5 K, respectively. The spinflip probability of the Cu layer was obtained using the temperature dependence of FMR linewidth. These results were then compared with the calculated data of the temperature dependence of spin-diffusion length. © 2006 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.45.3892

Scopus

Publisher：INTERMAG ASIA 2005: Digests of the IEEE International Magnetics Conference  

Scopus

Publisher：IEEE Transactions on Magnetics  

Intrinsic α-damping constants of Co2MnAl Heusler alloy films prepared by magnetron sputtering were investigated. After deposition of Co2MnAl films, the films were annealed at 200-400°C to control the crystal structure and the atomic order between Co, Mn, and Al sites. Ferromagnetic resonance (FMR) technique was used to obtain α values of Co2MnAl films in this study. Out-of-plane angular dependences of the resonance field (HR) and line width (ΔHpp) of FMR spectra were measured and fitted using the Landau-Lifshitz-Gilbert (LLG) equation. The authors were able to fit all experimental results well because of the lack of inhomogeneities in prepared Co2MnAl films. The α-damping constants obtained from the fitting results decreased with increasing annealing temperature and showed a minimum value of 0.007 at 300°C. It was found that a degree of B2 structure order can sensitively affect α-damping constants of Co2MnAl films. © 2005 IEEE.

DOI： 10.1109/TMAG.2005.854832

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