Article
Materials Science, Multidisciplinary
Cong He, Keisuke Masuda, Jieyuan Song, Thomas Scheike, Zhenchao Wen, Yoshio Miura, Tadakatsu Ohkubo, Kazuhiro Hono, Seiji Mitani, Hiroaki Sukegawa
Summary: This study systematically investigates the nano-crystal domain structures formed in MgO barrier and their effects on tunnel magnetoresistance (TMR) in epitaxial fcc-Co90Fe10 (CoFe)(111)/MgO(111)/CoFe(111) magnetic tunnel junctions (MTJs) using both experimental and first-principles methods. The results reveal the unique formation of nano-crystal domains in the (111)-textured MgO layer and identify three different orientation relationships (ORs) between CoFe and MgO. It is found that one of the ORs has a small contribution to the transport, which explains the discrepancy between experimental and theoretical TMR ratios.
Article
Physics, Applied
Yibing Zhao, Dunzhu Gesang, Cai Zhou, Guilin Chen, Cunxu Gao, Changjun Jiang
Summary: Investigations on Gilbert damping in epitaxial Heusler Co2FeAl films varying from 3 nm to 9 nm in thickness were conducted using broadband ferromagnetic resonance (FMR) in the temperature range of 5 K-300 K. The results showed a continuous decrease in Gilbert damping with increasing thickness of Co2FeAl films, as well as an enhanced peak of Gilbert damping observed at around 50 K, which was attributed to spin reorientation transition at the Co2FeAl/MgO interface. Additionally, analysis of the linewidth suggested that FMR linewidth in epitaxial Co2FeAl films was due to two-magnon scattering, originating from different order degrees of the B2 phase with the growth of CFA film impacting the control of magnetic damping in spin-based nanodevices.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2021)
Article
Nanoscience & Nanotechnology
Konstantin V. Larionov, Jose J. Pais Pereda, Songtian Li, Seiji Sakai, Pavel B. Sorokin
Summary: Integrating half-metallic materials and 2D spacers into vertical magnetoresistive spin valves may lead to effective low-power consumption storage and memory technologies. The study investigated magnetic tunnel junctions based on ferromagnetic CFGG Heusler alloy and MoS2 spacers of different thicknesses, demonstrating a large magnetoresistance value. The findings support the development of spintronics devices utilizing half-metallic Heusler alloys and diverse transition metal dichalcogenide family.
ACS APPLIED MATERIALS & INTERFACES
(2022)
Article
Physics, Applied
Aquil Ahmad, Srimanta Mitra, S. K. Srivastava, A. K. Das
Summary: A giant magnetocaloric effect was observed in Co2FeAl Heusler alloy nanoparticles near the ferromagnetic to paramagnetic phase transition, with a positive anomaly in magnetic entropy change and a linear increase with magnetic field. The nature of the phase transition was confirmed to be second-order based on the Arrott plot and universal curve analysis.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2021)
Article
Materials Science, Multidisciplinary
R. S. Malik, E. K. Delczeg-Czirjak, R. Knut, D. Thonig, I Vaskivskyi, D. Phuyal, R. Gupta, S. Jana, R. Stefanuik, Y. O. Kvashnin, S. Husain, A. Kumar, P. Svedlindh, J. Soderstrom, O. Eriksson, O. Karis
Summary: This report investigates optically induced ultrafast magnetization dynamics in the Heusler alloy Co2FeAl, finding that the demagnetization time is independent of structural order and the magnetization recovery time correlates strongly with the Gilbert damping parameter. The remagnetization process in Co2FeAl is dominated by magnon dynamics, with potential general applicability.
Article
Multidisciplinary Sciences
O. M. Chumak, A. Pacewicz, A. Lynnyk, B. Salski, T. Yamamoto, T. Seki, J. Z. Domagala, H. Glowinski, K. Takanashi, L. T. Baczewski, H. Szymczak, A. Nabialek
Summary: This study investigated the magnetoelastic effects in CFMS and CFGG Heusler alloy thin films, as well as the correlations between various magnetic properties. Non-Gilbert dissipation related contributions were found, including two-magnon scattering and spin pumping phenomena. The magnetoelastic constant values and effective magnetic damping parameter values were determined, revealing a range of -6 to 30x10(6) erg/cm(3) and 1 to 12x10(-3), respectively.
SCIENTIFIC REPORTS
(2021)
Article
Physics, Applied
Yechao Ling, Yong Hu, Xiaodan Chi, Jiawei Chen, Haobo Wang, Ben Niu, Di Wu, Mingxiang Xu, Zhida Han, Jun Du, Qingyu Xu
Summary: Heusler alloys exhibit anisotropic magnetostructural transitions under epitaxial strain, showing different magnetic behaviors in different orientations. This study demonstrates the influence of substrate on the magnetic properties of Heusler alloys and provides insights for designing novel magnetic devices.
JOURNAL OF APPLIED PHYSICS
(2022)
Article
Chemistry, Physical
Yu Zhang, Guanjie Wu, Weihua Zhu, Zhihao Ji, Q. Y. Jin, Zongzhi Zhang
Summary: The magnetization dynamics of epitaxially-grown Co2FeAl thin films were systematically investigated, revealing a four-fold symmetry in the dependencies of precession frequency, relaxation time, and magnetic damping factor on the orientation of applied magnetic field. Through the preparation of samples under various conditions, a significant Gilbert damping difference between the hard and easy axes was extracted, attributed to the in-plane magnetocrystalline anisotropy and anisotropic distribution of spin-orbit coupling. These findings provide new insights into the anisotropic properties of magnetization and damping, which are crucial for the design and optimization of advanced spintronic devices for different applications.
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2021)
Article
Physics, Atomic, Molecular & Chemical
Yu-jie Hu, Jing Huang, Jia-ning Wang, Qun-xiang Li
Summary: The study reveals that the magnetic tunnel junction exhibits near perfect spin-filtering effect in the parallel magnetization configuration, resulting in a huge tunneling magnetoresistance. This effect is mainly attributed to the half-metallic nature of Co2MnSi electrodes and the significant spin-polarization of the interfacial Ti 3d orbital.
CHINESE JOURNAL OF CHEMICAL PHYSICS
(2021)
Article
Nanoscience & Nanotechnology
Yu Zhang, Guanjie Wu, Zhihao Ji, Sai Zhou, Hongwei Xue, Ziyang Li, Siwei Zhang, Jingying Zhang, Yaowen Liu, Qingyuan Jin, Zongzhi Zhang
Summary: This study systematically investigates the temperature dependence of magnetization dynamics, particularly the magnetic damping anisotropy. It is found that the damping anisotropy undergoes a distinctive reorientation transition at around 200K as the temperature decreases. The competition between the intrinsic anisotropic distribution of bulk spin orbit coupling and the interfacial two-magnon scattering plays a crucial role in this reorientation. This research provides a clear understanding of damping anisotropy variation and the underlying mechanism, which is of great importance for designing spintronic devices with optimized dynamic magnetic properties.
ACS APPLIED MATERIALS & INTERFACES
(2022)
Article
Materials Science, Multidisciplinary
Shi-Qiang Wang, Ming-Zhi Wang, Yu-Fei Li, Wei Zhu, Zhi-Guo Wang, Zhong Shi
Summary: The investigation of magnetic domain wall resistance (DWR) in epitaxial Co2MnAl (CMA) thin films, a Heusler alloy, reveals a sign change phenomenon. This is due to the half-metallic band structure with high spin polarization, as verified by negative anisotropic magnetoresistance in the two-current model. The scattering relaxation time for majority and minority electrons experiences a dramatic change near the half-metallic band gap, resulting in an unusual upturned relaxation time ratio and sign change of intrinsic DWR. These findings enhance our understanding of spin-dependent dynamics in half metals and provide insights into entangled magnetoresistance in Heusler alloys with high spin polarization.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(2023)
Article
Materials Science, Multidisciplinary
Hui-Min Tang, Shi-Zhuo Wang, Xing-Tao Jia
Summary: We conducted a first-principles study on the tunneling anisotropic magnetoresistance (TAMR) in Ag(Ir,Pt)/MgO/Fe junctions. An enhanced TAMR effect of approximately 10% was found in these junctions at the equilibrium state, exhibiting ideal and skewed fourfold angular dependence for in-plane and out-of-plane TAMR, respectively. The TAMR effect showed a simple barrier thickness dependence, with the largest effect observed in the junction with a 6-monolayer MgO barrier. The complex and enhanced TAMR effect in these junctions is believed to be attributed to interfacial states induced by spin-orbit coupling, while even a slight interfacial oxygen vacancy disorder at the Fe/MgO interface can noticeably deteriorate the TAMR effect.
Article
Chemistry, Physical
Keun-Hong Min, Duk Hyun Lee, Sang-Jun Choi, In-Ho Lee, Junho Seo, Dong Wook Kim, Kyung-Tae Ko, Kenji Watanabe, Takashi Taniguchi, Dong Han Ha, Changyoung Kim, Ji Hoon Shim, Jonghwa Eom, Jun Sung Kim, Suyong Jung
Summary: The authors investigate the tunnelling magnetoresistance in Fe3GeTe2/hBN(WSe2)/Fe3GeTe2 magnetic tunnel junctions and report strong variations including polarization reversals with bias. Using van der Waals heterostructures with two-dimensional magnets, they demonstrate electrically tunable spin injection and detection, as well as modulated and reversed net spin polarization of the injected carriers, leading to changes in tunnelling magnetoresistance. The authors attribute the spin polarization reversals to contributions from high-energy localized spin states in the metallic ferromagnet, which is inaccessible in conventional magnetic junctions.
Article
Materials Science, Multidisciplinary
Suraj Singh, Nanhe Kumar Gupta, Soumyarup Hait, Sujeet Chaudhary, Thomas Tybell, Erik Wahlstrom
Summary: The investigation focused on the spin wave propagation in ion beam sputtered Co2FeAl Heusler alloy thin film on Si(100) substrate, with the estimation of technologically relevant parameters such as group velocity, attenuation length, and Gilbert damping parameter. The frequency dependency of these parameters was observed, showing variations with increasing frequency. The propagation parameters were independently verified using time-resolved propagating spin wave spectroscopy.
MATERIALS RESEARCH EXPRESS
(2021)
Article
Nanoscience & Nanotechnology
Yeong Jae Shin, Juan Jiang, Yichen Jia, Frederick J. Walker, Charles H. Ahn
Summary: BaTiO3 exhibits functional properties like high dielectric constant, large Pockels coefficient, and strong ferroelectricity/piezoelectricity, which can be used for various applications including non-volatile memory devices. Synthesis of BaTiO3 thin films by molecular beam epitaxy allows for growth of coherently strained and ferroelectric BaTiO3 at low temperatures, paving the way for large-scale integration with mainstream electronics platforms. Experimental results demonstrate surface mobility of BaO and TiO2 adatoms conducive to ferroelectric crystal growth at low temperatures.
Article
Physics, Applied
Mahmoud Rasly, Tomoya Nakatani, Jiangnan Li, Hossein Sepehri-Amin, Hiroaki Sukegawa, Yuya Sakuraba
Summary: In this study, amorphous CoFeBTa (CFBT) was investigated as a soft magnetic layer for the free layer (FL) of magnetic tunnel junctions, leading to linear resistance-magnetic field (R-H) response curves with low hysteresis. The highest TMR ratio and sensitivity were achieved with a specific CFBT/Ta/CoFeB FL composition. The devices showed superior detectivity (D) for magnetic field sensing compared to previously reported TMR sensors with NiFe soft magnetic layers.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2021)
Review
Materials Science, Multidisciplinary
Kelvin Elphick, William Frost, Marjan Samiepour, Takahide Kubota, Koki Takanashi, Hiroaki Sukegawa, Seiji Mitani, Atsufumi Hirohata
Summary: Heusler alloys are theoretically predicted to potentially become half-metals at room temperature. These alloys have advantages such as good lattice matching with major substrates, high Curie temperature above RT, and controllability for spin density of states at the Fermi energy level. They are categorized into half- and full-Heusler alloys based on crystalline structures, with discussions both experimentally and theoretically.
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS
(2021)
Article
Materials Science, Multidisciplinary
N. Zhao, A. Sud, H. Sukegawa, S. Komori, K. Rogdakis, K. Yamanoi, J. Patchett, J. W. A. Robinson, C. Ciccarelli, H. Kurebayashi
Summary: Current-induced spin torques were studied in epitaxial NiMnSb films on a commercially available epiready GaAs substrate, showing a symmetry that matches those expected from spin-orbit interaction in a tetragonally distorted half-Heusler crystal. Both fieldlike and dampinglike torques were observed in all samples tested, and the efficiency of the current-induced torques was comparable to that of ferromagnetic metal/heavy-metal bilayers.
PHYSICAL REVIEW MATERIALS
(2021)
Article
Physics, Applied
Thomas Scheike, Qingyi Xiang, Zhenchao Wen, Hiroaki Sukegawa, Tadakatsu Ohkubo, Kazuhiro Hono, Seiji Mitani
Summary: Giant tunnel magnetoresistance (TMR) ratios were achieved in epitaxial Fe/MgO/Fe(001) exchange-biased spin-valve magnetic tunnel junctions by tuning growth conditions for each layer and growing on a highly (001)-oriented Cr buffer layer. Specific features include symmetric differential conductance spectra and plateau-like deep local minima in dI/dV.
APPLIED PHYSICS LETTERS
(2021)
Article
Physics, Applied
Ke Tang, Zhenchao Wen, Yong-Chang Lau, Hiroaki Sukegawa, Takeshi Seki, Seiji Mitani
Summary: This study investigates magnetization switching induced by spin-orbit torque in Co2MnGa magnetic Weyl semimetal thin films, demonstrating a relatively large spin Hall efficiency and exploring various characteristics such as second harmonic signals, thickness dependence of spin Hall efficiency, and shift of anomalous Hall loops under applied currents. The research contributes to understanding mechanisms of spin-current generation and potential applications of magnetic WSMs in spintronic devices.
APPLIED PHYSICS LETTERS
(2021)
Article
Physics, Applied
Thomas Scheike, Zhenchao Wen, Hiroaki Sukegawa, Seiji Mitani
Summary: This article reports large TMR ratios in Fe/Mg-rich spinel/Fe(001) MTJs prepared using Mg4Al-O-x barrier, reaching 429% at room temperature and 1034% at 10 K. The resistance oscillations, significantly enhanced compared to Fe/MgO/Fe(001) MTJs, resulted in a large peak-to-valley difference of 125% at room temperature. Improved barrier interfaces were demonstrated by the Mg4Al-O-x barrier.
APPLIED PHYSICS LETTERS
(2022)
Article
Multidisciplinary Sciences
Kenta Sato, Hiroaki Sukegawa, Kentaro Ogata, Gang Xiao, Hideo Kaiju
Summary: The magnetocapacitance (MC) effect has been observed in systems where both symmetries of time-reversal and space-inversion are broken. An epitaxial MTJ structure with MgAl2O4(001) barrier has shown a tunnel magnetocapacitance (TMC) effect exceeding 420% at room temperature, providing deeper understanding of the intrinsic mechanism of the TMC effect.
SCIENTIFIC REPORTS
(2022)
Article
Nanoscience & Nanotechnology
S. Nezu, T. Scheike, H. Sukegawa, K. Sekiguchi
Summary: The propagation characteristics of backward-volume magnetostatic spin-waves in epitaxial Fe(001) films were studied. The backward-volume spin-wave exhibited a complicated packet propagation due to the combination of cubic-magnetocrystalline anisotropy and anisotropic spin-wave dispersion. The group velocity of the spin wave was greatly enhanced at low external magnetic fields and propagation occurred even under no magnetic field.
Article
Chemistry, Multidisciplinary
Ke Tang, Zhenchao Wen, Takeshi Seki, Hiroaki Sukegawa, Seiji Mitani
Summary: This work investigates the effects of Ni and Fe doping and interface properties on spin-orbit torques (SOTs) in a topological semimetal CoSi. It is found that the doping of Ni and Fe reduces the spin Hall efficiency, while the insertion of a Cu layer at the interface enhances the spin Hall efficiency.
ADVANCED MATERIALS INTERFACES
(2022)
Article
Physics, Applied
Thomas Scheike, Zhenchao Wen, Hiroaki Sukegawa, Seiji Mitani
Summary: We demonstrate high tunnel magnetoresistance (TMR) ratios of up to 631% at room temperature (RT) and 1143% at 10 K using CoFe/MgO/CoFe(001) epitaxial magnetic tunnel junctions (MTJs). The large TMR ratios are achieved through fine-tuning of atomic-scale structures and through the insertion of ultrathin CoFe and Mg layers, which enhance coherent tunneling transport and contribute to the significant TMR oscillation effect. The oscillation phenomenon dominates the transport behavior and can reach a peak-to-valley difference exceeding 140% at RT.
APPLIED PHYSICS LETTERS
(2023)
Article
Nanoscience & Nanotechnology
Jieyuan Song, Cong He, Thomas Scheike, Zhenchao Wen, Hiroaki Sukegawa, Tadakatsu Ohkubo, Yukio Nozaki, Seiji Mitani
Summary: In this work, fully epitaxial Ru/Cu heterostructures were fabricated with interface engineering and nanolayer insertions. The atomically controlled interface was confirmed by high-resolution scanning transmission electron microscopy, and the spin current generation and efficiency were evaluated. The results show that the insertion of Cu/Ru nanolayers improves the spin Hall efficiency, and a large effective spin Hall conductivity is achieved in the epitaxial Ru/Cu hybrid nanolayers.
Article
Materials Science, Multidisciplinary
Hayato Nakayama, Taisuke Horaguchi, Cong He, Hiroaki Sukegawa, Tadakatsu Ohkubo, Seiji Mitani, Kazuto Yamanoi, Yukio Nozaki
Summary: We demonstrate spin-torque generation using a compositional gradient at the interface of titanium and tungsten thin films. By varying the width of the compositional gradient interface (CGI) between films, spin-torque ferromagnetic resonance is observed in a ferromagnetic alloy. The width dependence of the spin torque is associated with the generation of spin and/or orbital angular momentum flow at the CGI.
Review
Computer Science, Information Systems
Atsufumi Hirohata, David C. Lloyd, Takahide Kubota, Takeshi Seki, Koki Takanashi, Hiroaki Sukegawa, Zhenchao Wen, Seiji Mitani, Hiroki Koizumi
Summary: Spintronic devices show promise in replacing nanoelectronic memories and sensors due to their efficiency and scalability. To achieve further miniaturization, new materials development is necessary, such as increasing spin polarization or using antiferromagnets. Recent studies have found interesting properties in antiferromagnetic materials, such as 100% spin-polarized current and topological effects. This review summarizes the recent development of three types of antiferromagnets and discusses their potential for device applications.
Article
Materials Science, Multidisciplinary
Cong He, Keisuke Masuda, Jieyuan Song, Thomas Scheike, Zhenchao Wen, Yoshio Miura, Tadakatsu Ohkubo, Kazuhiro Hono, Seiji Mitani, Hiroaki Sukegawa
Summary: This study systematically investigates the nano-crystal domain structures formed in MgO barrier and their effects on tunnel magnetoresistance (TMR) in epitaxial fcc-Co90Fe10 (CoFe)(111)/MgO(111)/CoFe(111) magnetic tunnel junctions (MTJs) using both experimental and first-principles methods. The results reveal the unique formation of nano-crystal domains in the (111)-textured MgO layer and identify three different orientation relationships (ORs) between CoFe and MgO. It is found that one of the ORs has a small contribution to the transport, which explains the discrepancy between experimental and theoretical TMR ratios.
Article
Materials Science, Multidisciplinary
Keisuke Masuda, Hiroyoshi Itoh, Yoshiaki Sonobe, Hiroaki Sukegawa, Seiji Mitani, Yoshio Miura
Summary: In this study, we theoretically investigate the tunnel magnetoresistance (TMR) effect in (111)-oriented magnetic tunnel junctions (MTJs) with SrTiO3 barriers, specifically Co/SrTiO3/Co(111) and Ni/SrTiO3/Ni(111). Our analysis combining first-principles calculations and the Landauer formula reveals that the Co-based MTJ exhibits a high TMR ratio (>500%), while the Ni-based MTJ has a smaller TMR ratio (290%). This difference is attributed to the band folding phenomenon and the half-metallic band structure in the Lambda(1) state of Co (Ni), as well as the variation in the s-orbital weights at the Fermi level.
