担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Excitation of magnetization dynamics in magnetic materials, especially in ultrathin ferromagnetic films, is of utmost importance for developing various ultrafast spintronics devices. Recently, the excitation of magnetization dynamics, i.e. ferromagnetic resonance (FMR) via electric field-induced modulation of interfacial magnetic anisotropies, has received particular attention due to several advantages, including lower power consumption. However, several additional torques generated by unavoidable microwave current induced because of the capacitive nature of the junctions may also contribute to the excitation of FMR apart from electric field-induced torques. Here, we study the FMR signals excited by applying microwave signal across the metal-oxide junction in CoFeB/MgO heterostructures with Pt and Ta buffer layers. Analysis of the resonance line shape and angular dependent behavior of resonance amplitude revealed that apart from voltage-controlled in-plane magnetic anisotropy (VC-IMA) torque a significant contribution can also arises from spin-torques and Oersted field torques originating from the flow of microwave current through metal-oxide junction. Surprisingly, the overall contribution from spin-torques and Oersted field torques are comparable to the VC-IMA torque contribution, even for a device with negligible defects. This study will be beneficial for designing future electric field-controlled spintronics devices.

DOI： 10.1088/1361-648X/acc377

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担当区分：最終著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Spintronic devices, such as spin Hall oscillators (SHOs) and spin transfer torque oscillators, have become popular candidates for use as the reservoir in the reservoir computing (RC) architecture. The memory capacity of a reservoir quantifies the amount of information retained at any given time, indicating its significance for different RC tasks. In this work, we consider an SHO, consisting of a bilayer structure of platinum/Permalloy, as the reservoir. Using micromagnetic simulations, we evaluate the change in memory capacity of the SHO system as the magnetization dynamics varies from transient state oscillations to limit cycle oscillations. We also perform a three-bit parity task to study the performance of the oscillator in carrying out a nonlinear task. A time series prediction task, namely, the nonlinear auto regressive moving average (NARMA)2 task, is also performed. The results of both tasks confirm a correlation between the evaluated memory capacity of the reservoir and its efficiency in performing temporal tasks. The best performance in RC tasks is observed when the output magnetization dynamics of the oscillator consists of both transient state and limit cycle oscillations.

DOI： 10.1109/TMAG.2023.3266517

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Ferromagnet/nonmagnet (FM/NM) bilayer-based spin Hall nano-oscillators (SHNOs) - a sub-class of spintronic oscillator devices - have promising potential toward realizing low-power physical reservoir computing systems because of their inherent nonlinearity and miniature form factor. However, most of the studies on SHNOs indicate that an external biasing magnetic field is necessary for their operation, creating a bottleneck for their practical implementation in designing small and compact RC hardware. In this report, using micromagnetic simulation, we demonstrate biasing field-free operation of a FM/NM bilayer-based SHNO by exploiting the magnetic anisotropy. Our results reveal that the magnetic anisotropy in the FM layer provides active control over the DC tunability of auto-oscillation frequency and the threshold value of current needed for sustained auto-oscillations. We show that the increase in uniaxial anisotropy substantially modifies the spatial profile of auto-oscillation and eventually leads to the reduction in the threshold current for auto-oscillation, which could be utilized to design low-power computing hardware using SHNO devices.

DOI： 10.1063/5.0130624

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担当区分：最終著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

The rapidly evolving utilization of spin Hall effect (SHE) arising from spin-orbit coupling in 5d transition metals and alloys has made giant strides in the development of designing low-power, robust, and nonvolatile magnetic memory. Recent studies, on incorporating nonmetallic lighter elements such as oxygen, nitrogen, and sulfur into 5d transition metals, have shown an enhancement in dampinglike torque efficiency θDL due to the modified SHE, but the mechanism behind this enhancement is not clear. In this paper, we study θDL at different temperatures (100-293 K) to disentangle the intrinsic and extrinsic side-jump scattering induced SHE in N-implanted Pt. We observe a crossover of intrinsic to extrinsic side-jump mechanism as the implantation dose increases from 2×1016 to 1×1017ions/cm2. A sudden decrease in the intrinsic spin Hall conductivity is counterbalanced by the increase in the extrinsic side-jump induced SHE efficiency. These results conclude that studying θDL as a function of implantation dose, and as a function of temperature, is important to understand the physical mechanism contributing to SHE.

DOI： 10.1103/PhysRevB.107.064402

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記述言語：英語   掲載種別：研究論文（学術雑誌）

The impurity incorporation in host high spin-orbit coupling materials like platinum (Pt) has shown improved charge-to-spin conversion e±ciency by modifying the up-spin and down-spin electrons trajectories via bending or skewing them in opposite directions. This enables e±cient generation, manipulation, and transport of spin currents. In this study, we irradiated the Pt thin films with pulsed hot dense oxygen plasma in non-focus mode operation and analyzed the spin Hall angle of the oxygen plasma irradiated Pt films using spin torque ferromagnetic resonance (ST-FMR). Our results demonstrate a 2.4 times enhancement in the spin Hall angle after transient oxygen plasma treatment of Pt as compared to pristine Pt. This improvement might be because of the introduction of disorder and defects in the Pt lattice due to transient oxygen plasma processing, which enhanced the spin-orbit coupling and leads to more e±cient charge-to-spin conversion without breaking the spin-orbit torque symmetries. Our findings offer a new method of dense plasma focus device-based modification of material for the development of advanced spintronic devices based on Pt and other heavy metals.

DOI： 10.1142/S2010324723400246

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Femtosecond laser-induced photoexcitation of ferromagnet (FM)/heavy metal (HM) heterostructures has attracted attention by emitting broadband terahertz frequencies. The phenomenon relies on the formation of an ultrafast spin current, which is primarily attributed to the direct photoexcitation of the FM layer. However, during the process, the FM layer also experiences a secondary excitation led by the hot electrons from the HM layer that travel across the FM/HM interface and transfer additional energy in the FM. Thus, the generated secondary spins enhance the total spin current formation and lead to amplified spintronic terahertz emission. These results emphasize the significance of the secondary spin current, which even exceeds the primary spin currents when FM/HM heterostructures with thicker HM are used. An analytical model is developed to provide deeper insights into the microscopic processes within the individual layers, underlining the generalized ultrafast superdiffusive spin-transport mechanism.

DOI： 10.1002/adom.202301027

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担当区分：最終著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

In this work, we employ micromagnetic modelling of a spin Hall oscillator for a direct inference and classification of binary digit inputs. The spectral characteristics of the oscillation is utilized for the classification. We observed a direct inference of binary digit inputs up to a sequence of four binary digits. Subsequently, handwritten digit image recognition is tested with the Modified National Institute of Standards and Testing (MNIST) handwritten digit database and acquired an accuracy of 88.6% with a linear classifier network.

DOI： 10.1109/INTERMAGShortPapers58606.2023.10228745

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Electrical control of photogenerated terahertz (THz) spin current pulses from a spintronic emitter has been at the forefront for the development of scalable, cost-efficient, wideband optospintronic devices. Artificially combined ferroelectric and ferromagnet heterostructure provides the potential avenue to deterministically control the phase of THz spin current pulse through piezoelectric strain. Here, the electric field-mediated piezoelectric strain control of photogenerated THz spin current pulse from a multiferroic spintronic emitter is demonstrated. The phase reversal of the THz spin current pulse is obtained from the combined effect of piezoelectric strain and a small magnetic field applied opposite to the initial magnetization of the ferromagnet. The piezoelectric strain-controlled phase switching of THz spin current thus opens a door to develop efficient strain engineered scalable on-chip THz spintronics devices.

DOI： 10.1002/adom.202201929

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担当区分：最終著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Inspired by the success of field-effect transistors in electronics, electric field controlled magnetization dynamics has emerged as an important integrant in low-power spintronic devices. Here, we demonstrate electric field induced parametric excitation for CoFeB/MgO junctions by using interfacial in-plane magnetic anisotropy (IMA). When the IMA and the external magnetic field are parallel to each other, magnons are efficiently excited by electric field induced parametric resonance. The corresponding wavelengths are estimated to be tuned down to exchange interaction length scales by changing the input power and frequency of the applied voltage. A generalized phenomenological model is developed to explain the underlying role of the electric field torque. Electric field control of IMA is shown to be the origin for excitation of both uniform and parametric resonance modes in the in-plane magnetized sample, a crucial element for purely electric field induced magnetization dynamics. Electric field excitation of exchange magnons, with no Joule heating, offers a good opportunity for developing nanoscale magnonic devices and exploring various nonlinear dynamics in nanomagnetic systems.

DOI： 10.1103/PhysRevResearch.4.023139

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記述言語：英語   掲載種別：研究論文（学術雑誌）

In the present work, temperature dependent magnetic, structural and electronic properties of FeTa films with increasing Ta concentration are investigated. X-ray reflectivity (XRR) studies reveal densification of the film with increasing Ta concentration. Thermal annealing also results in an increased electron density relative to as-deposited film, concurrent with increase in grain size as observed from X-ray diffraction (XRD) and results of Soft-X-ray absorption spectroscopy (SXAS). However, grain growth is inhibited with increasing Ta concentration by presence of Ta in grain boundary (GB) region. This also results in increase in magnetic coercivity (greater than150 %) as observed from magneto-optical Kerr effect (MOKE). The structural properties were further correlated with magnetic properties as observed from Polarized neutron reflectivity (PNR) and Ferromagnetic resonance (FMR). Effective magnetic moment of the samples, as observed from PNR decreases with increasing Ta concentration and increases with increasing annealing temperature, which is in agreement with FMR results. Scattering length density profiles, observed from simultaneous fitting of XRR and PNR show presence of an oxide layer at surface, as also confirmed from SXAS measurements.

DOI： 10.1016/j.jmmm.2021.168306

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Directional specific control on the generation and propagation of magnons is essential for designing future magnon-based logic and memory devices for low power computing. The epitaxy of the ferromagnetic thin film is expected to facilitate anisotropic linewidths, which depend on the crystal cut and the orientation of the thin film. Here, we have shown the growth-induced magneto-crystalline anisotropy in 40 nm epitaxial yttrium iron garnet (YIG) thin films, which facilitate cubic and uniaxial in-plane anisotropy in the resonance field and linewidth using ferromagnetic resonance measurements. The growth-induced cubic and non-cubic anisotropy in epitaxial YIG thin films are explained using the short-range ordering of the Fe3+ cation pairs in octahedral and tetrahedral sublattices with respect to the crystal growth directions. This site-preferred directional anisotropy enables an anisotropic magnon-magnon interaction and opens an avenue to precisely control the propagation of magnonic current for spin-transfer logics using YIG-based magnonic technology.

DOI： 10.1063/5.0064653

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記述言語：英語   掲載種別：研究論文（学術雑誌）

We study the implications of FeCo underlayer and overlayer on the static and dynamic magnetic properties of FeCo/FePt exchange spring system along with post-annealing kinetics. Probing of FePt/FeCo/Si and FeCo/FePt/Si bilayers using high energy synchrotron X-ray diffraction by varying glancing angles unveiled structural variations at the interface, where FeCo is observed to inhibit the crystalline growth of FePt. A soft ferromagnetic in-plane behavior and defect-driven hard ferromagnetic properties in the out-plane configuration are established. Besides, the magnetization dynamics studied by Ferromagnetic Resonance depicts an out-plane magnetization component of FePt only in FeCo/FePt/Si. X-ray Absorption Spectroscopy (XAS) in the Fe, Co and Pt L-edge regions reveal dissimilar interfaces in the two series due to thermal agitation effects. XAS spectra at Fe and Co K-edges ensure similar local coordination of Co immaterial of stack order, contrary to altered local geometry of Fe observed in the two series ascribed to varied crystallinity of FePt. Such structures are useful for spin-wave assisted low field magnetization switching in highly coercive FePt by using exchange coupled soft FeCo.

DOI： 10.1016/j.jallcom.2021.160249

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記述言語：英語   掲載種別：研究論文（学術雑誌）

ConspectusIn this Account, we describe the challenges and promising applications of transmission electron microscopy (TEM) imaging and spectroscopy at cryogenic temperatures. Our work focuses on two areas of application: the delay of electron-beam-induced degradation and following low-temperature phenomena in a continuous and variable temperature range. For the former, we present a study of LiMn1.5Ni0.5O4 lithium ion battery cathode material that undergoes electron beam-induced degradation when studied at room temperature by TEM. Cryogenic imaging reveals the true structure of LiMn1.5Ni0.5O4 nanoparticles in their discharged state. Improved stability under electron beam irradiation was confirmed by following the evolution of the O K-edge fine structure by electron energy-loss spectroscopy. Our results demonstrate that the effect of radiation damage on discharged LiMn1.5Ni0.5O4 was previously underestimated and that atomic-resolution imaging at cryogenic temperature has a potential to be generalized to most of the Li-based materials and beyond. For the latter, we present two studies in the imaging of low-temperature phenomena on the local scale, namely, the evolution of ferroelectric and ferromagnetic domains walls, in BaTiO3 and Y3Fe5O12 systems, respectively, in a continuous and variable temperature range. Continuous imaging of the phase transition in BaTiO3, a prototypical ferroelectric system, from the low-temperature orthorhombic phase continuously up to the centrosymmetric high-temperature phase is shown to be possible inside a TEM. Similarly, the propagation of domain walls in Y3Fe5O12, a magnetic insulator, is studied from ∼120 to ∼400 K and combined with the application of a magnetic field and electrical current pulses to mimic the operando conditions as in domain wall memory and logic devices for information technology. Such studies are promising for studying the pinning of the ferroelectric and magnetic domains versus temperature, spin-polarized current, and externally applied magnetic field to better manipulate the domain walls. The capability of combining operando TEM stimuli such as current, voltage, and/or magnetic field with in situ TEM imaging in a continuous cryogenic temperature range will allow the uncovering of fundamental phenomena on the nanometer scale. These studies were made possible using a MEMS-based TEM holder that allowed an electron-transparent sample to be transferred and electrically contacted on a MEMS chip. The six-contact double-tilt holder allows the alignment of the specimen into its zone axis while simultaneously using four electrical contacts to regulate the temperature and two contacts to apply the electrical stimuli, i.e., operando TEM imaging. This Account leads to the demonstration of (i) the high-resolution imaging and spectroscopy of nanoparticles oriented in the desired [110] zone-axis direction at cryogenic temperatures to mitigate the electron beam degradation, (ii) imaging of low-temperature transitions with accurate and continuous control of the temperature that allowed single-frame observation of the presence of both the orthorhombic and tetragonal phases in the BaTiO3 system, and (iii) magnetic domain wall propagation as a function of temperature, magnetic field, and current pulses (100 ns with a 100 kHz repetition rate) in the Y3Fe5O12 system.

DOI： 10.1021/acs.accounts.1c00078

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Heated dot magnetic recording (HDMR) provides a path to increase the areal density of magnetic recording media beyond 4 Tb/in2. HDMR-based recording media requires ultrasmall, noninteracting, and thermally stable magnetic dots with high perpendicular anisotropy. We have synthesized nonstoichiometric Fe60Pt40nanoclusters with and without a Pt buffer layer on silicon substrates, which shows a reduction in chemical ordering temperatures. The Fe60Pt40nanoclusters retain the hard magnetic phase up to 1023 K with the coercive field of 1.3 Tesla due to the Pt element compensation from the buffer layer. This compensation of Pt was confirmed through X-ray diffraction (XRD) investigations where two distinct phases of Fe3Pt and FePt3are observed at elevated annealing temperatures. Micromagnetic simulations were performed to understand the effect of magnetic anisotropy, dipolar interaction, and exchange coupling between the soft magnetic Fe3Pt and hard magnetic FePt. The results imply that nonstoichiometric Fe60Pt40with the Pt buffer layer facilitates low chemical ordering temperatures retaining the high perpendicular anisotropy with minimal noninteracting behavior, suitable for HDMR.

DOI： 10.1021/acsanm.1c01085

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Damping-like torque (DLT) arising from the spin Hall effect (SHE) in heavy metals and their alloys has been widely explored for applications in spin-orbit torque MRAM, auto-oscillations, spin waves, and domain wall motion. In conventional materials, the DLT efficiency is limited by intrinsic properties, while attaining strong spin-orbit coupling and higher spin-charge interconversion, with no compromise to electric properties, is the need of the hour. In this Letter, we report more than 3.5 times increase in DLT efficiency, θDL, of modified Pt-oxide by employing a better approach of low energy 20 keV O+ ion implantation. The highest fluence of O+ implantation (1 × 1017 ions cm−2) in Pt enhanced the DLT efficiency from 0.064 to 0.230 and improved the spin transmission for a smaller trade-off in the longitudinal resistivity (ρPt to ρPt−Oxide) from 55.4 to 159.5 μΩ cm, respectively. The transverse spin Hall resistivity, ρSH, is found to be proportional to the square of the longitudinal resistivity, i.e., ρSHimp∝ρimp2, implying that the enhanced SHE in O-implanted Pt is due to a side-jumping mechanism. Further, no break in the twofold as well as mirror symmetry of torques from the O-implanted Pt allows the use of spin-torque ferromagnetic resonance-based line shape analysis to quantify such torques.

DOI： 10.1063/5.0054779

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Dissipationless and scattering-free spin-based terahertz electronics is the futuristic technology for energy-efficient information processing. Femtosecond light pulse provides an ideal pathway for exciting the ferromagnet (FM) out-of-equilibrium, causing ultrafast demagnetization and superdiffusive spin transport at sub-picosecond timescale, giving rise to transient terahertz radiation. Concomitantly, light pulses also deposit thermal energy at short timescales, suggesting the possibility of abrupt change in magnetic anisotropy of the FM that could cause ultrafast photo-thermal switching (PTS) of terahertz spin currents. Here, a single light pulse induced PTS of the terahertz spin current manifested through the phase reversal of the emitted terahertz photons is demonstrated. The switching of the transient spin current is due to the reversal of the magnetization state across the energy barrier of the FM layer. This demonstration opens a new paradigm for on-chip spintronic devices enabling ultralow-power hybrid electronics and photonics fueled by the interplay of charge, spin, thermal, and optical signals.

DOI： 10.1002/adfm.202010453

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

High efficiency of charge–spin interconversion in spin Hall materials is a prime necessity to apprehend intriguing functionalities of spin–orbit torque for magnetization switching, auto-oscillations, and domain wall motion in energy-efficient and high-speed spintronic devices. To this end, innovations in fabricating advanced materials that possess not only large charge–spin conversion efficiency but also viable electrical and spin Hall conductivity are of importance. Here, a new spin Hall material designed by implanting low energy 12 keV sulfur ions in heavy metal Pt, named as Pt(S), is reported that demonstrates eight times higher conversion efficiency as compared to pristine Pt. The figure of merit, spin Hall angle (θ ), up to (Formula presented.) of 0.502 together with considerable electrical conductivity (Formula presented.) of 1.65 × 10 Ω m is achieved. The spin Hall conductivity (Formula presented.) increases with increasing (Formula presented.), as (Formula presented.), implying an intrinsic mechanism in a dirty metal conduction regime. A comparatively large (Formula presented.) of 8.32 × 10 ((Formula presented.)) Ω m among the reported heavy-metals-based alloys can be useful for developing next-generation spintronic devices using spin–orbit torque. SH 6 –1 –1 5 –1 –1

DOI： 10.1002/qute.202000112

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記述言語：英語   掲載種別：研究論文（学術雑誌）

The atomically flat interface of the Y3Fe5O12 (YIG) thin film and the Gd3Ga5O12 (GGG) substrate plays a vital role in obtaining the magnetization dynamics of YIG below and above the anisotropy field. Here, magnetoimpedance (MI) is used to investigate the magnetization dynamics in fully epitaxial 45 nm YIG thin films grown on the GGG (001) substrates using a copper strip coil in the MHz-GHz frequency region. The resistance (R) and reactance (X), which are components of impedance (Z), allow us to probe the absorptive and dispersive components of the dynamic permeability, whereas a conventional spectrometer only measures the field derivative of the power absorbed. The distinct excitation modes arising from the resonance in the uniform and dragged magnetization states of YIG are respectively observed above and below the anisotropy field. The magnetodynamics clearly shows the visible dichotomy between two resonant fields below and above the anisotropy field and its motion as a function of the direction of the applied magnetic field. A low value of a damping factor of ∼4.7 - 6.1 × 10-4 is estimated for uniform excitation mode with an anisotropy field of 65 ± 2 Oe. Investigation of below and above anisotropy field-dependent magnetodynamics in the low-frequency mode can be useful in designing the YIG-based resonators, oscillators, filters, and magnonic devices.

DOI： 10.1021/acsami.0c13213

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Precession trajectories during excitation of magnetization dynamics play an important role in determining spin wave propagation, emission power of spin torque oscillator, and spin current generated by spin pumping. However, comparatively little information has emerged on the effect of perpendicular magnetic anisotropy (PMA) on dynamical magnetization trajectories. The effect of PMA on magnetization dynamics has become particularly important since the discovery of voltage control of magnetic anisotropy in CoFeB/MgO junctions. This motivates us to investigate the effect of PMA on dynamical magnetization trajectories of CoFeB thin films using micromagnetic simulations. The ellipticity of the trajectories is found to increase monotonically with PMA. On the other hand, the area of such elliptical trajectories, which determine the spin current generation, shows a non-monotonous change with respect to PMA. This area can be expected to be maximum for the case where ellipticity is 0.5.

DOI： 10.1109/TMAG.2020.2987288

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Magnetoelectric coupling in metal/oxide heterostructures has opened up the possibility of controlling magnetization by voltage, i.e., electric field. However, the electric-field excitation of magnetization dynamics in perfectly in-plane and out-of-plane magnetized films have not been demonstrated so far due to zero electric-field torque originating from voltage control of perpendicular magnetic anisotropy. This limits the application of voltage-controlled magnetic anisotropy in magnetic field free control of magnetization dynamics. Here we show that magnetic annealing can induce an interfacial in-plane magnetic anisotropy of CoFeB/MgO junctions, thereby controlling the symmetry of interfacial magnetic anisotropy. The magnetic anisotropy is modulated by applying voltage: a negative bias voltage increases perpendicular magnetic anisotropy, while a positive bias voltage decreases perpendicular magnetic anisotropy and increases the in-plane magnetic anisotropy. Such a control of symmetry of the interfacial magnetic anisotropy by magnetic annealing and its tunability by electric fields is useful for developing purely voltage-controlled spintronic devices.

DOI： 10.1103/PhysRevB.101.174405

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2020 IEEE. The easy cone state of magnetization that arises as a result of a competition between the second- A nd fourth-order perpendicular magnetic anisotropies has the advantage of a non-zero electric-field torque without the application of a bias magnetic field and is thus a potential candidate for purely voltage-driven magnetic storage devices. In this article, the onset of the easy cone state of magnetization is simulated in a ferromagnet film. Subsequently, the switching field and time for voltage-controlled magnetization switching process are studied as a function of the inclination angle of the easy cone state from the film normal in the range of 0°-45°. The switching field is found to decrease with decreasing anisotropy. The switching time is found to become faster for higher inclination angle of the easy cone state due to an increase in its torque.

DOI： 10.1109/TMAG.2019.2942339

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Herein, spin transport dynamics across asymmetric Fe50Pt50/Cu/Fe20Ni80 soft-magnetic trilayer structure is reported and thereby modulation of magnetic parameters including damping and effective field is determined by means of the angular dependence of broadband ferromagnetic resonance measurements. At distinct precession of individual magnetic layer, spin-pumping is found to be prevalent with expected linewidth increase. Mutual precession for wide range of resonance configuration reveals a collective reduction in anisotropy field of around 200 mT for both Fe50Pt50 and Fe20Ni80 systems. Subsequent observation of no-excess interface damping shows the possible control of spin-pumping effect by tuning the net flow of spin-current in a multilayer structure. These experimental findings have significance for microwave devices that require tunable anisotropy field in magnetic multilayers.

DOI： 10.1002/pssr.201900267

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© MYU K.K. Nanoscale sensing applications require significant power to operate, which can be largely supplied through the efficient management of omnipresent heat. The spin Seebeck effect (SSE) is rather a fresh energy harvesting phenomenon that enables the conversion of a temperature gradient across magnetic materials into spin current. This spin current can further be converted into charge current by adjoining heavy metals to the magnet. In this study, we fabricated the thermoelectric multilayer films of bismuth-substituted neodymium iron garnet (Nd2Bi1Fe5O12) (NIG) as well as gallium and bismuth co-substituted neodymium iron garnet (Nd2Bi1Fe4Ga1O12) (NIGG) on (111)-oriented gallium gadolinium garnet substrates by metal organic decomposition. The thicknesses of the NIG and NIGG multilayers are varied to control the magnetic properties. The observed spin Seebeck signal is found to be directly dependent on the garnet/heavy metal interface and tends to decrease in intensity with increasing amount of NIGG in the garnet multilayers. Our results emphasize the importance of magnet/ heavy metal interface properties for designing SSE-based sensors.

DOI： 10.18494/SAM.2019.2335

Kyutacar

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85071332329&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 The Author(s). Voltage or electric field induced magnetization dynamics promises low power spintronics devices. For successful operation of some spintronics devices such as magnetic oscillators and magnetization switching devices a clear understanding of nonlinear magnetization dynamics is required. Here, we report a detailed experimental and micromagnetic simulation study about the effect of excitation power on voltage induced local magnetization dynamics in an ultrathin CoFeB film. Experimental results show that the resonance line-width and frequency remains constant, whereas cone angle of the magnetization precession increases linearly with square-root of excitation power below threshold value, known as linear excitation regime. Above threshold power, the dynamics enters into nonlinear regime where resonance line-width monotonically increases and resonance frequency monotonically decreases with increasing excitation power. Simulation results reveal that a strong nonlinear and incoherent magnetization dynamics are observed in our experiment above the threshold power which reduces dynamic magnetic signal by suppressing large cone angle of magnetization precession. Moreover, a significant transfer of spin angular momentum from uniform FMR mode to its degenerate spin waves outside of excitation area further restrict the cone angle of precession within only few degrees in our device. Our results will be very useful to develop all-voltage-controlled spintronics devices.

DOI： 10.1038/s41598-017-02427-3

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85019912847&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 Author(s). Spin waves (SWs) may be used as potential information carriers in next generation low-power spintronics devices. Here, we report an experimental study on the excitation of propagating magnetostatic surface SWs by voltage-controlled magnetic anisotropy in a 2 nm thick CoFeB film. The SWs are detected by a pico-second time-resolved longitudinal Kerr microscope with a spatial resolution of 600 nm. We found a linear increase in the SW amplitude with the applied rf voltage. We show that in this ultrathin film, the voltage excited SWs can propagate up to micrometer distances which decrease with the increase in the bias magnetic field value. This is also supported by micromagnetic simulation results. Furthermore, we show that voltage excitations are spatially localized as opposed to conventional microstrip antenna induced Oersted field excitations. We discuss about the advantage of voltage excitation compared to the Oersted field excitation. We believe that voltage excitation of SWs will be more suitable and useful for the development of all-voltage-controlled nanoscale spintronics devices with a high density of integration.

DOI： 10.1063/1.4990724

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85026883889&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）

© The Author(s) 2017. Recent progress in magnetic tunnel junctions (MTJs) with a perpendicular easy axis consisting of CoFeB and MgO stacking structures has shown that magnetization dynamics are induced due to voltage-controlled magnetic anisotropy (VCMA), which will potentially lead to future low-power-consumption information technology. For manipulating magnetizations in MTJs by applying voltage, it is necessary to understand the coupled magnetization motion of two magnetic (recording and reference) layers. In this report, we focus on the magnetization motion of two magnetic layers in MTJs consisting of top layers with an in-plane easy axis and bottom layers with a perpendicular easy axis, both having perpendicular magnetic anisotropy. According to rectified voltage (V rec ) measurements, the amplitude of the magnetization motion depends on the initial angles of the magnetizations with respect to the VCMA direction. Our numerical simulations involving the micromagnetic method based on the Landau-Lifshitz-Gilbert equation of motion indicate that the magnetization motion in both layers is induced by a combination of VCMA and transferred angular momentum, even though the magnetic easy axes of the two layers are different. Our study will lead to the development of voltage-controlled MTJs having perpendicular magnetic anisotropy by controlling the initial angle between magnetizations and VCMA directions.

DOI： 10.1038/srep42511

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85013324850&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 Author(s). Here, we investigate the spin Hall angle of Pt in a Ni 80 Fe 20 /Pt bilayer system by using a broadband spin pumping and inverse spin Hall effect measurement. An out-of-plane excitation geometry with an application of external magnetic field perpendicular to the charge current direction is utilized in order to suppress unwanted galvanomagnetic effects. Magnetization precession angle (θ C ) on ferromagnetic resonance for wide excitation frequency range (4-14 GHz) is estimated from the rectification voltage of anisotropic magnetoresistance (AMR) and a conventional method of using the microwave power in a coplanar waveguide. A marked difference in θ C profiles for the different methods is observed, resulting in the large variation in estimated values of spin current density at Ni 80 Fe 20 /Pt interface. The frequency dependence of the spin current density estimated using the AMR effect is found to be similar to that of the inverse spin Hall voltage. We obtain the frequency-invariant spin Hall angle of 0.067 ± 0.002.

DOI： 10.1063/1.4973704

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85009374156&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2016 Macmillan Publishers Limited. All rights reserved. Spin-momentum locking in the Dirac surface state of a topological insulator (TI) offers a distinct possibility for highly efficient charge-to-spin current (C-S) conversion compared with spin Hall effects in conventional paramagnetic metals. For the development of TI-based spin current devices, it is essential to evaluate this conversion efficiency quantitatively as a function of the Fermi level position E F. Here we introduce a coefficient q ICS to characterize the interface C-S conversion effect by means of the spin torque f erromagnetic resonance (ST-FMR) for (Bi 1'x Sb x) 2 Te 3 thin films as E F is tuned across the bandgap. In bulk insulating conditions, the interface C-S conversion effect via the Dirac surface state is evaluated as having large, nearly constant values of q ICS, reflecting that q ICS is inversely proportional to the Fermi velocity v F, which is almost constant. However, when E F traverses through the Dirac point, the q ICS is remarkably reduced, possibly due to inhomogeneity of k F and/or instability of the helical spin structure. These results demonstrate that fine tuning of E F in TI-based heterostructures is critical in maximizing the efficiency using the spin-momentum locking mechanism.

DOI： 10.1038/nphys3833

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84979600051&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2016 Author(s). IV-VI diluted magnetic semiconductor Ge 1-x Cr x Te layers up to x = 0.1 were grown on SrF 2 substrates by molecular beam epitaxy. In situ reflection high-energy electron diffraction shows a streaky pattern with a sixfold symmetry in the plane for the Ge 1-x Cr x Te layer, implying an epitaxial growth of Ge 1-x Cr x Te (111)/SrF 2 (111). A clear hysteresis loop is observed in the anomalous Hall effect measurements due to the strong spin-orbit interaction in the host GeTe. The Curie temperature increases with increasing Cr composition up to 200 K, but there is no clear dependence of the Curie temperature on the hole concentration, implying that the mechanism of the ferromagnetic interaction among Cr ions is different from Mn doped diluted magnetic semiconductors.

DOI： 10.1063/1.4953042

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84974569609&origin=inward

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/1.4931697

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1016/j.physe.2014.11.023

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.7567/APEX.7.113002

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1103/PhysRevB.89.081308

Scopus

記述言語：英語   掲載種別：記事・総説・解説・論説等（商業誌、新聞、ウェブメディア）

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.7567/APEX.7.023006

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1038/ncomms3893

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/1.4824897

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/1.4804990

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1002/adfm.201202545

Scopus

担当区分：責任著者   記述言語：日本語   掲載種別：記事・総説・解説・論説等（商業誌、新聞、ウェブメディア）

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/1.4776699

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1038/srep00628

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/1.4737001

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1021/nn300421c

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記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/1.3672402

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1021/nn202791g

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1143/APEX.4.113003

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1109/TMAG.2011.2159367

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1143/APEX.4.093004

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1109/TMAG.2011.2108272

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1038/nmat3046

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1103/PhysRevLett.106.197203

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1103/PhysRevLett.106.226601

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/1.3556759

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/1.3562904

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1088/0022-3727/43/42/422001

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/1.3460909

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1143/APEX.3.063002

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記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

開催期間： 2023年06月   記述言語：英語   開催地：Singapore  

その他リンク： https://www.icmat2023.mrs.org.sg/public.asp?page=program_overview.asp

開催期間： 2023年06月   記述言語：英語   開催地：Singapore  

その他リンク： https://www.icmat2023.mrs.org.sg/public.asp?page=program_overview.asp

開催期間： 2023年05月   記述言語：英語   開催地：Sendai  

その他リンク： https://2023.intermag.org/

開催期間： 2023年05月   記述言語：英語   開催地：Sendai  

その他リンク： https://2023.intermag.org/

開催期間： 2023年03月18日   記述言語：日本語  

開催期間： 2023年03月15日   記述言語：日本語  

開催期間： 2023年03月06日   記述言語：英語  

開催期間： 2022年12月14日   記述言語：英語  

開催期間： 2022年12月14日   記述言語：英語  

開催期間： 2022年11月16日   記述言語：英語  

開催期間： 2022年11月16日   記述言語：英語  

開催期間： 2022年11月02日   記述言語：英語  

開催期間： 2022年07月28日   記述言語：英語  

開催期間： 2022年03月18日 - 2022年03月19日   記述言語：英語  

開催期間： 2022年03月18日 - 2022年03月19日   記述言語：英語  

開催期間： 2022年03月12日 - 2022年03月18日   記述言語：英語  

開催期間： 2020年12月06日 - 2020年12月10日   記述言語：英語  

開催期間： 2020年12月06日 - 2020年12月10日   記述言語：英語  

開催期間： 2020年12月06日 - 2020年12月10日   記述言語：英語  

開催期間： 2020年12月02日 - 2020年12月06日   記述言語：英語  

開催期間： 2020年11月26日 - 2020年11月28日   記述言語：英語   開催地：virtual  

開催期間： 2020年11月26日 - 2020年11月28日   記述言語：英語   開催地：virtual  

開催期間： 2019年11月04日 - 2019年11月08日   記述言語：英語  

開催期間： 2019年07月08日 - 2019年07月10日   記述言語：英語  

開催期間： 2019年06月23日 - 2019年06月28日   記述言語：英語  

開催期間： 2018年12月15日   記述言語：英語  

開催期間： 2018年12月15日   記述言語：英語  

開催期間： 2018年12月09日 - 2018年12月13日   記述言語：英語  

開催期間： 2018年10月09日 - 2018年10月12日   記述言語：英語  

開催期間： 2018年10月09日 - 2018年10月12日   記述言語：英語  

開催期間： 2017年11月15日   記述言語：英語  

開催期間： 2017年11月15日   記述言語：英語  

開催期間： 2016年12月18日   記述言語：英語  

開催期間： 2016年12月18日   記述言語：英語  

開催期間： 2016年11月   記述言語：英語  

開催期間： 2016年11月   記述言語：英語  

開催期間： 2016年10月   記述言語：英語  

開催期間： 2016年08月   記述言語：英語  

開催期間： 2016年01月   記述言語：英語  

開催期間： 2016年01月   記述言語：英語  

開催期間： 2015年08月   記述言語：英語  

開催期間： 2014年12月   記述言語：英語  

開催期間： 2014年12月   記述言語：英語  

開催期間： 2014年12月   記述言語：英語  

開催期間： 2014年05月   記述言語：英語  

開催期間： 2013年12月13日   記述言語：英語  

開催期間： 2013年07月13日   記述言語：英語  

開催期間： 2013年07月13日   記述言語：英語  

開催期間： 2013年05月13日   記述言語：英語  

開催期間： 2013年05月13日   記述言語：英語  

開催期間： 2013年05月13日   記述言語：英語  

開催期間： 2013年05月13日   記述言語：英語  

開催期間： 2013年01月13日   記述言語：英語  

開催期間： 2013年01月13日   記述言語：英語  

開催期間： 2013年01月13日   記述言語：英語  

開催期間： 2013年01月13日   記述言語：英語  

開催期間： 2012年12月04日   記述言語：英語  

開催期間： 2012年10月12日   記述言語：英語  

開催期間： 2012年10月12日   記述言語：英語  

開催期間： 2012年10月12日   記述言語：英語  

開催期間： 2012年10月12日   記述言語：英語  

開催期間： 2012年10月12日   記述言語：英語  

開催期間： 2012年10月12日   記述言語：英語  

開催期間： 2012年08月12日   記述言語：英語  

開催期間： 2012年07月12日   記述言語：英語  

開催期間： 2012年07月12日   記述言語：英語  

開催期間： 2012年07月12日   記述言語：英語  

開催期間： 2012年07月12日   記述言語：英語  

開催期間： 2012年07月12日   記述言語：英語  

開催期間： 2012年05月12日   記述言語：英語  

開催期間： 2012年02月   記述言語：英語  

開催期間： 2011年11月02日 - 2011年11月03日   記述言語：英語  

開催期間： 2011年11月02日 - 2011年11月03日   記述言語：英語  

開催期間： 2011年11月02日 - 2011年11月03日   記述言語：英語  

開催期間： 2011年10月31日   記述言語：英語  

開催期間： 2011年10月03日   記述言語：英語  

開催期間： 2011年09月   記述言語：英語  

開催期間： 2011年06月12日 - 2011年06月13日   記述言語：英語  

開催期間： 2011年04月11日   記述言語：英語  

開催期間： 2011年04月11日   記述言語：英語  

開催期間： 2011年04月11日   記述言語：英語  

開催期間： 2011年04月11日   記述言語：英語  

開催期間： 2010年12月   記述言語：英語  

開催期間： 2010年11月   記述言語：英語  

開催期間： 2010年11月   記述言語：英語  

開催期間： 2010年11月   記述言語：英語  

開催期間： 2010年09月19日 - 2010年09月24日   記述言語：英語  

開催期間： 2010年09月19日 - 2010年09月24日   記述言語：英語  

開催期間： 2010年09月19日 - 2010年09月24日   記述言語：英語  

開催期間： 2010年09月13日 - 2010年09月17日   記述言語：英語  

開催期間： 2010年07月05日 - 2010年07月08日   記述言語：英語  

開催期間： 2010年07月05日 - 2010年07月08日   記述言語：英語  

開催期間： 2010年05月30日 - 2010年06月04日   記述言語：英語  

開催期間： 2010年01月18日 - 2010年01月22日   記述言語：英語  

発表言語：英語   講演種別：招待講演  

開催期間： 2018年12月18日 - 2018年12月22日   発表言語：英語   講演種別：招待講演  

発表言語：英語   講演種別：招待講演  

開催期間： 2018年12月09日 - 2018年12月13日   発表言語：英語   講演種別：招待講演  

開催期間： 2018年01月19日 - 2018年01月20日   発表言語：英語   講演種別：招待講演  

発表言語：英語   講演種別：招待講演  

開催期間： 2017年11月15日   発表言語：英語   講演種別：特別講演  

開催期間： 2016年09月   発表言語：英語   講演種別：特別講演  

開催期間： 2016年08月   発表言語：英語   講演種別：特別講演  

開催期間： 2015年01月10日   発表言語：英語   講演種別：特別講演