Article
Physics, Applied
Chaoliang Zhang, Yutaro Takeuchi, Shunsuke Fukami, Hideo Ohno
Summary: In this study, we investigate the magnetization switching using a combination of STT and SOT, finding that SOT allows for fast switching of magnetization and STT eliminates the need for an external field. The results show that in the short pulse regime, the Type X structure achieves a switching current one-fourth smaller than the Type Y structure at 200 ps.
APPLIED PHYSICS LETTERS
(2021)
Article
Materials Science, Multidisciplinary
Tatsuya Yamamoto, Rie Matsumoto, Takayuki Nozaki, Hiroshi Imamura, Shinji Yuasa
Summary: This article reviews the current research status of magnetization switching utilizing the voltage-controlled magnetic anisotropy (VCMA) effect. It focuses on subnanosecond voltage pulses driven magnetization switching as a promising alternative to the existing spin-transfer-torque technology used in magnetic random-access memories. However, practical issues such as write-error rate, narrow operating window, and the need for an external bias magnetic field are faced by VCMA-driven magnetization switching. Recent developments in the field of VCMA studies are introduced to address these issues from both experimental and theoretical perspectives. Possible material designs for enhancing both the energy efficiency and reliability of VCMA-driven magnetization switching are also discussed.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(2022)
Article
Engineering, Electrical & Electronic
Rachit R. Pandey, Sutapa Dutta, Heston A. Mendonca, Ashwin A. Tulapurkar
Summary: We have studied the influence of edge roughness on the electrical transport properties of magnetic tunnel junctions using non-equilibrium Green's function formalism. Edge roughness is modeled as a stochastic variation in the cross-sectional profile of the junction, characterized by the stretched exponential decay of the correlation function. The stochastic variation in shape and size leads to changes in the transverse energy mode profile, resulting in variations in resistance and switching voltage. We propose a model for efficient calculation of edge roughness effects by approximating the cross-sectional geometry to a circle or an ellipse.
IEEE ELECTRON DEVICE LETTERS
(2023)
Article
Engineering, Electrical & Electronic
Deyuan Lyu, Pravin Khanal, Yang Lv, Bowei Zhou, Hwanhui Yun, Qi Jia, Brandon R. Zink, Yihong Fan, K. Andre Mkhoyan, Weigang Wang, Jian-Ping Wang
Summary: This study investigates Mo-based perpendicular magnetic tunnel junctions (Mo-pMTJs), which exhibit superior perpendicular magnetic anisotropy (PMA) and thermal tolerance compared to mainstream Ta-pMTJs. The ultrafast switching behavior of Mo-pMTJ devices is explored, with a focus on the precessional regime at sub-ns timescales. The optimization of switching energy is discussed. Furthermore, the magneto-transport properties and switching behavior of Mo-pMTJs at low temperatures down to 2 K are investigated, demonstrating the feasibility of utilizing Mo-pMTJ devices in cryogenic memory applications.
IEEE ELECTRON DEVICE LETTERS
(2022)
Article
Chemistry, Physical
Qizhong Zhao, Fanghua Tian, Tieyan Chang, Kaiyan Cao, Dingchen Wang, Yin Zhang, Chao Zhou, Xiaoqin Ke, Wenliang Zuo, Yu Wang, Sen Yang, Xiaoping Song
Summary: In this study, the magnetization reversal phenomenon in the Ni20Mn3B6 alloy was investigated at low applied fields, revealing two compensation temperatures. The first temperature is attributed to competition between Mn atoms at different positions, while the second arises from moment rotation to satisfy Zeeman energy. This phenomenon enables tunable switching of magnetization between positive and negative values, providing potential applications in spintronic devices and magnetic storage materials.
JOURNAL OF ALLOYS AND COMPOUNDS
(2021)
Article
Chemistry, Multidisciplinary
Delin Zhang, Mukund Bapna, Wei Jiang, Duarte Sousa, Yu-Ching Liao, Zhengyang Zhao, Yang Lv, Protyush Sahu, Deyuan Lyu, Azad Naeemi, Tony Low, Sara A. Majetich, Jian-Ping Wang
Summary: In this study, the authors demonstrate a bipolar electric field effect switching using voltage-controlled exchange coupling, which shows potential applications in energy-efficient memory and logic devices. The results indicate that this type of switch has a lower switching current density, which could eliminate major obstacles in the development of spin memory devices.
Article
Engineering, Electrical & Electronic
Wenlong Cai, Kewen Shi, Yudong Zhuo, Daoqian Zhu, Yan Huang, Jialiang Yin, Kaihua Cao, Zhaohao Wang, Zongxia Guo, Zilu Wang, Gefei Wang, Weisheng Zhao
Summary: The study demonstrates sub-nanosecond field-free switching by the interplay of STT and SOT in perpendicular magnetic tunnel junctions, showing that applying SOT current can significantly decrease the incubation time and current density of STT for ultra-fast switching.
IEEE ELECTRON DEVICE LETTERS
(2021)
Article
Engineering, Electrical & Electronic
Min Wang, Zhaohao Wang, Xueying Zhang, Weisheng Zhao
Summary: Researchers have investigated the conditions for achieving field-free switching by combining spin-orbit torque and Dzyaloshinskii-Moriya interaction, using the ratio of domain wall width to nanodot diameter as a criterion. The study highlights the importance of decreasing the surface energy of magnetic domain walls to allow the existence of metastable states.
IEEE ELECTRON DEVICE LETTERS
(2021)
Article
Nanoscience & Nanotechnology
Shih-Che Kao, Chun-Yi Lin, Wei-Bang Liao, Po-Chuan Wang, Chen-Yu Hu, Yu-Hao Huang, Yan-Ting Liu, Chi-Feng Pai
Summary: In order to make spin-orbit torque magnetic random access memory (SOT-MRAM) more practical, achieving current-induced magnetization switching without an external bias field is crucial. This study investigates the field-free switching mechanism in CoFeB/W/CoFeB T-type structures and identifies the Néel orange-peel effect as the dominant origin of the built-in bias field. The film roughness is found to positively correlate with the field-free switching efficacy, and further optimization is achieved through roughness tuning.
Article
Computer Science, Hardware & Architecture
Kezhou Yang, Dhuruva Priyan, Abhronil Sengupta
Summary: Brain-inspired computing is a promising pathway to solve challenges in deep learning. This article proposes using temporal information encoding in probabilistic neuromorphic systems as a different approach and considers superparamagnetic tunnel junctions as a potential solution.
IEEE TRANSACTIONS ON COMPUTER-AIDED DESIGN OF INTEGRATED CIRCUITS AND SYSTEMS
(2023)
Article
Physics, Multidisciplinary
Christos Thanos, Ioannis Panagiotopoulos
Summary: Micromagnetic simulations are used to study resonances and microwave assisted magnetic switching (MAS) in two-phase Co/CoPt nanowires. The nucleation, interfacial domain wall pinning, and propagation processes are well distinguished and play a role in the system. The coupling strength varies to cover different hysteresis curves. Interfacial resonances play an important role in MAS, allowing for optimal conditions with low MAS frequencies and dc applied fields while balancing low field usage and short reversal time.
Article
Chemistry, Multidisciplinary
Hendrik Meer, Felix Schreiber, Christin Schmitt, Rafael Ramos, Eiji Saitoh, Olena Gomonay, Jairo Sinova, Lorenzo Baldrati, Mathias Klaeui
Summary: Researchers have unraveled the mechanism of current-induced magnetic switching in insulating antiferromagnet/heavy metal systems using concurrent transport and magneto-optical measurements. Different final states of the switching in specially engineered NiO/Pt bilayers devices were observed with different electrical pulsing and device geometries, attributed to the thermomagnetoelastic switching mechanism combined with thermal excitations. This noncontact mechanism provides a potential explanation for previously reported contradicting observations of switching final state attributed to spin-orbit torque mechanisms.
Article
Multidisciplinary Sciences
Shinji Isogami, Yohei Shiokawa, Atsushi Tsumita, Eiji Komura, Yugo Ishitani, Kosuke Hamanaka, Tomohiro Taniguchi, Seiji Mitani, Tomoyuki Sasaki, Masamitsu Hayashi
Summary: The study evaluated magnetization switching driven by spin-orbit torque in three terminal magnetic tunnel junctions, showing that the conventional thermally assisted magnetization switching model cannot describe SOT induced switching using short current pulses.
SCIENTIFIC REPORTS
(2021)
Article
Physics, Applied
Tatsuya Yamamoto, Tomohiro Ichinose, Jun Uzuhashi, Takayuki Nozaki, Tadakatsu Ohkubo, Kay Yakushiji, Shingo Tamaru, Hitoshi Kubota, Akio Fukushima, Kazuhiro Hono, Shinji Yuasa
Summary: In this study, we investigate the perpendicular magnetic anisotropy (PMA) in MgO/CoFeB (CFB)/MgO junctions by introducing an angstrom-thick Mo spacer layer. It is found that perpendicularly magnetized CFB/Mo/CFB films can be obtained for a wide range of CFB thicknesses, achieving a large PMA energy density. The voltage-controlled magnetic anisotropy effect shows a sign inversion between the 'top free' and 'bottom free' magnetic tunnel junctions, indicating the importance of the flatness of the CFB/MgO interface for improving the efficiency of the effect.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2022)
Article
Chemistry, Physical
Ruiheng Zhang, Aina He, Lei Xie, Jianhua Zhang, Yaqiang Dong, Jiawei Li, Bojun Zhang, Yanxin Liu
Summary: In this study, transverse magnetic field annealing was applied to a high saturation induction alloy, leading to improved high-frequency properties and refined magnetic domains. Additionally, the role of dual anisotropies on magnetic performance was investigated, providing guidance for optimizing the performance of common mode chokes.
JOURNAL OF ALLOYS AND COMPOUNDS
(2022)
Article
Physics, Applied
Hiroyasu Nakayama, Takayuki Nozaki, Tomohiro Nozaki, Shinji Yuasa
Summary: We investigated the voltage-controlled magnetic anisotropy (VCMA) effect in Co/MgO junctions by inserting a sub-atomic layer of heavy metals at the interface. The electrical control of the magnetic anisotropy was evaluated using a micro-magneto-optical Kerr effect magnetometer. The results showed that the VCMA coefficient of the Co/MgO junctions increased with the insertion of an Ir or Pt layer, while decreased with the insertion of an Os layer. This suggests that the VCMA coefficient can be engineered by doping heavy metals at the interface. The interface engineering using a heavy metal layer provides a method to control the VCMA coefficient over a wide range.
APPLIED PHYSICS LETTERS
(2023)
Article
Multidisciplinary Sciences
Xianzhe Chen, Tomoya Higo, Katsuhiro Tanaka, Takuya Nomoto, Hanshen Tsai, Hiroshi Idzuchi, Masanobu Shiga, Shoya Sakamoto, Ryoya Ando, Hidetoshi Kosaki, Takumi Matsuo, Daisuke Nishio-Hamane, Ryotaro Arita, Shinji Miwa, Satoru Nakatsuji
Summary: The tunnelling magnetoresistance (TMR) in magnetic tunnel junctions (MTJs) is usually studied in ferromagnetic materials, but this study reports the observation of TMR in an all-antiferromagnetic tunnel junction. A TMR ratio of about 2% was measured at room temperature, which is attributed to the configuration of cluster magnetic octupoles in the chiral antiferromagnetic state. Sign and direction of anisotropic longitudinal spin-polarized current in the antiferromagnet can be controlled by octupole direction. Theoretical analysis suggests that the chiral antiferromagnetic MTJ can produce a substantially large TMR ratio due to the time-reversal, symmetry-breaking polarization characteristic of cluster magnetic octupoles.
Article
Optics
Y. Shimotsuma, K. Kinouchi, R. Yanoshita, M. Fujiwara, N. Mizuochi, M. Uemoto, M. Shimizu, K. Miura
Summary: The NV centers in a diamond were successfully created using a femtosecond laser single pulse. The effect of different laser pulse widths on the diamond lattice was investigated both experimentally and theoretically. Interestingly, despite the high thermal conductivity of a diamond, a suitable pulse repetition rate of several tens kHz was found for the formation of NV center ensembles by femtosecond laser pulse irradiation.
Article
Nanoscience & Nanotechnology
Minori Goto, Ryo Ishikawa, Hikaru Nomura, Yoshishige Suzuki
Summary: Skyrmions are topological spin textures that exhibit Brownian motion in solids, and have attracted research interest for device applications and investigation of new physical phenomena utilizing stochastic behavior. However, the sensitivity of skyrmions to changes in magnetic properties and the aging variation pose challenges for reproducibility and device stability. This study demonstrates that aging variation can be suppressed by a quick 3-minute annealing in air, and identifies surface oxidation as the main mechanism. Avoiding surface oxidation can effectively mitigate the aging variation of skyrmions. This work accelerates the understanding of skyrmion Brownian motion and facilitates device applications of stochastic systems.
Article
Physics, Applied
Atsushi Sugihara, Tomohiro Ichinose, Shingo Tamaru, Tatsuya Yamamoto, Makoto Konoto, Takayuki Nozaki, Shinji Yuasa
Summary: We deposited a 1.1 nm ultrathin CoFeB layer as the storage layer for MgO-based magnetic tunnel junctions in spin-transfer-torque (STT) magnetoresistive random-access memory (MRAM) on phi 300 mm wafers at 100 K, and investigated its effect on the magnetization dynamics of CoFeB. The results show that deposition at cryogenic temperatures is an effective manufacturing process for high-quality magnetic thin films with low magnetic damping, achieved through the improvement in the interfacial quality.
APPLIED PHYSICS EXPRESS
(2023)
Article
Physics, Applied
Hiroshige Deguchi, Tsukasa Hayashi, Hiroya Saito, Yoshiki Nishibayashi, Minori Teramoto, Masanori Fujiwara, Hiroki Morishita, Norikazu Mizuochi, Natsuo Tatsumi
Summary: We have developed a compact and portable measuring instrument using diamond NV centers, which can be powered by a laptop computer's USB 3.0. The portability is achieved by low power consumption of the optics, thanks to the diamond corner cube that enhances the current of the photodiode by 2.1 times compared to planar diamond, and the microwave source that reduced power consumption by 20 dB using a microwave resonator with a λ/4 open stub to magnetically drive the NV center. These results contribute to the social implementation of diamond sensors.
APPLIED PHYSICS EXPRESS
(2023)
Article
Physics, Applied
M. Haruyama, H. Kato, M. Ogura, Y. Kato, D. Takeuchi, S. Yamasaki, T. Iwasaki, H. Morishita, M. Fujiwara, N. Mizuochi, T. Makino
Summary: In this study, electrical excitation and detection of electroluminescence (EL) of single negatively charged nitrogen vacancy (NV-) centers were achieved using lateral diamond p(+)-i(n(-))-n(+) diodes. The efficiency of the electrical excitation rate of the NV center was significantly enhanced by introducing this diode structure compared to previous vertical diode structures. The charge state of the NV center could be manipulated by the voltage applied to the diode, leading to increased dominance of NV- in the emission of EL.
APPLIED PHYSICS LETTERS
(2023)
Article
Physics, Applied
Yuta Kobayashi, Yoichi Shiota, Hideki Narita, Teruo Ono, Takahiro Moriyama
Summary: The study reveals that the Joule heating induced by voltage pulses can cause a magnetic phase transition in D0(19)-Mn3Sn, altering the energy landscape relevant to spin-orbit torque switching. This poses challenges in accurately determining the thermal stability factor and highlights the importance of cautious estimation.
APPLIED PHYSICS LETTERS
(2023)
Article
Multidisciplinary Sciences
Naoki Fukumoto, Ryo Ohshima, Motomi Aoki, Yuki Fuseya, Masayuki Matsushima, Ei Shigematsu, Teruya Shinjo, Yuichiro Ando, Shoya Sakamoto, Masanobu Shiga, Shinji Miwa, Masashi Shiraishi
Summary: The large anisotropy of the effective g-factor in bismuth leads to a significant spin conversion anisotropy, which has important implications for understanding spin physics in condensed matter systems.
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
(2023)
Article
Physics, Applied
S. Funada, Y. Ishikawa, M. Kimata, K. Hayashi, T. Sano, K. Sugi, Y. Fujii, S. Mitsudo, Y. Shiota, T. Ono, T. Moriyama
Summary: In this study, we demonstrate the electrical detection of antiferromagnetic dynamics in ferrimagnetic Gd-Co thin films using a 154-GHz gyrotron. The captured resonant modes allow us to characterize the peculiar magnetization dynamics in Gd-Co. This milestone towards THz measurements for antiferro-and ferrimagnetic thin films has important implications.
PHYSICAL REVIEW APPLIED
(2023)
Article
Physics, Applied
Hiroki Morishita, Naoya Morioka, Testuri Nishikawa, Hajime Yao, Shinobu Onoda, Hiroshi Abe, Takeshi Ohshima, Norikazu Mizuochi
Summary: In this study, positive contrast in photocurrent detected magnetic resonance (PDMR) of nitrogen-vacancy (N-V) centers in diamond is observed. The sign of the PDMR contrast depends on the difference in the photocurrent generated from the excited states and the metastable state of N-V centers. Additionally, noise suppression using a phase-cycling-based noise-canceling technique is introduced to achieve electrically detected ac magnetic field sensing with a sensitivity of 29 nT Hz-1/2.
PHYSICAL REVIEW APPLIED
(2023)
Article
Materials Science, Multidisciplinary
Takahiro Moriyama, Luis Sanchez-Tejerina, Kent Oda, Takuo Ohkochi, Motoi Kimata, Yoichi Shiota, Hiroyuki Nojiri, Giovanni Finocchio, Teruo Ono
Summary: In this paper, the evolutions of antiferromagnetic domains in NiO under magnetic fields are experimentally investigated and numerically simulated. A micromagnetic framework with a simulation algorithm is extended to reproduce the domain patterns and provide detailed understanding of the domain evolutions. This work offers an important theoretical methodology to predict and understand the behaviors of micromagnetic structures in antiferromagnets.
PHYSICAL REVIEW MATERIALS
(2023)
Article
Optics
Masanori Fujiwara, Shunsuke Inoue, Shin-ichiro Masuno, Haining Fu, Shigeki Tokita, Masaki Hashida, Norikazu Mizuochi
Summary: Recently, the creation of nitrogen-vacancy (NV) centers using ultrashort laser processing has gained attention for quantum information devices. This study demonstrates the creation of high-density NV centers in a wide region using a single intense femtosecond laser pulse, which is important for quantum sensing applications. The technique allows for the expansion of the region containing NV centers and has the potential to fabricate ultrahigh-sensitivity quantum sensors.
Article
Engineering, Electrical & Electronic
Tomohiro Ichinose, Tatsuya Yamamoto, Takayuki Nozaki, Kay Yakushiji, Shingo Tamaru, Makoto Konoto, Shinji Yuasa
Summary: We developed a cryogenic temperature deposition process for high-performance CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) on φ300 mm thermally oxidized silicon wafers. The effect of deposition temperature on CoFeB layers and its impact on nanostructure, magnetic, and magneto-transport properties of MTJs were investigated. Cryogenic deposition of CoFeB at 100 K resulted in enhancements of perpendicular magnetic anisotropy (PMA) and voltage-controlled magnetic anisotropy (VCMA) of the MTJs compared to room temperature deposition. Improved interfacial qualities at the MgO/CoFeB interfaces were observed with cryogenic temperature deposition.
ACS APPLIED ELECTRONIC MATERIALS
(2023)
Article
Materials Science, Multidisciplinary
Jieyi Chen, Shoya Sakamoto, Hidetoshi Kosaki, Shinji Miwa
Summary: In this study, we investigate the effect of alkali halide layer insertion on perpendicular magnetic anisotropy (PMA) at the Fe/MgO interface by fabricating epitaxial Fe/alkali halide (LiF, NaCl, or CsI)/MgO multilayers using molecular beam epitaxy. It is found that an ultrathin LiF layer (0.1-0.4 nm) enhances interfacial PMA, while thicker LiF layer insertion (0.6-1 nm) weakens it. For CsI and NaCl cases, interfacial PMA energy decreases with increasing CsI or NaCl thickness. The study suggests that well-defined Fe-anion orbital hybridization achieved by good lattice matching and anion atoms with high electronegativities, such as F, are beneficial for interfacial PMA.
