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, Multidisciplinary
Geunwoo Kim, Soogil Lee, Sanghwa Lee, Byonggwon Song, Byung-Kyu Lee, Duhyun Lee, Jin Seo Lee, Min Hyeok Lee, Young Keun Kim, Byong-Guk Park
Summary: This study investigates the effects of annealing on the tunnel magnetoresistance ratio in CoFeB/MgO/CoFeB-based magnetic tunnel junctions with different capping layers and correlates them with microstructural changes. The findings indicate that the proper selection of a capping layer can increase the annealing temperature of MTJs, making it compatible with the complementary metal-oxide-semiconductor backend process.
Article
Materials Science, Multidisciplinary
A. Meo, S. Sampan-a-pai, P. B. Visscher, R. Chepulskyy, D. Apalkov, J. Chureemart, P. Chureemart, R. W. Chantrell, R. F. L. Evans
Summary: The study investigates the spin transfer torque switching dynamics in CoFeB/MgO/CoFeB magnetic tunnel junctions using atomistic simulations based on Slonczewski's model. The results demonstrate a magnetization reversal driven by the combination of coherent and nonuniform excitation modes, affected by factors such as current density, temperature, and structural imperfections. This deeper understanding can be valuable for spin transfer torque dynamics in nanoscale devices.
Article
Physics, Applied
Zhiqiang Cao, Weibin Chen, Shiyang Lu, Shaohua Yan, Yu Zhang, Zitong Zhou, Yaodi Yang, Zhi Li, Weisheng Zhao, Qunwen Leng
Summary: This paper introduces a double-interface CoFeB/MgO p-TMR structure to improve thermal stability of MTJ-based devices, and investigates the performance of TMR film stacks by varying the thickness of the MgO cap layer. It is found that decreasing the MgO cap layer thickness enhances sensitivity and linear output of the sensing layer.
APPLIED PHYSICS LETTERS
(2021)
Article
Physics, Applied
S. Tacchi, F. Casoli, M. G. Pini, A. Rettori, M. Madami, J. Akerman, T. T. Le, Q. N. Pham, H. L. Pham, T. N. Anh Nguyen
Summary: Utilizing alternating gradient force magnetometry and Brillouin light scattering experiments, this study investigated perpendicular magnetic anisotropy localized at the CoFeB-MgO interface in different heterostructures. Thermal treatment was found to significantly increase the PMA, and analysis of spin wave frequencies allowed estimation of the thickness dependence of PMA in a single CoFeB film. Additionally, the study of magnetic tunnel junctions revealed an antiferromagnetic interlayer exchange coupling between CoFeB layers that increased after annealing.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2021)
Article
Nanoscience & Nanotechnology
Hua Lv, Joao Fidalgo, Ana Silva, Diana C. Leitao, Thomas Kampfe, Juergen Langer, Jerzy Wrona, Berthold Ocker, Paulo P. Freitas, Susana Cardoso
Summary: The research demonstrated multi-level switching in single perpendicular magnetic tunnel junctions (p-MTJs) and showed the potential of high-performance multi-level p-MTJs for new generation spintronic devices. Using CoFeB/MgO/CoFeB based nano-scale p-MTJs, the study achieved multi-level switching with reliable set-reset operations, suggesting feasible strategies for improving multi-level switching through materials optimization and device geometry.
ADVANCED ELECTRONIC MATERIALS
(2021)
Article
Materials Science, Multidisciplinary
Tatsuya Yamamoto, Takayuki Nozaki, Kay Yakushiji, Shingo Tamaru, Hitoshi Kubota, Akio Fukushima, Shinji Yuasa
Summary: The study shows that Ta layer in MgO/Ta/CoFeB/MgO junctions can enhance the PMA of magnetic films and eliminate the diffusion of Ta, leading to superior thermal stability and the release of VCMA effect. In addition, the Co-Fe compositional variation in CoFeB layer associated with Ta insertion is related to the changes in PMA and VCMA.
Article
Physics, Applied
Hua Lv, Joao Fidalgo, Thomas Kampfe, Juergen Langer, Jerzy Wrona, Berthold Ocker, Paulo P. Freitas, Susana Cardoso
Summary: This study systematically investigates the Seebeck effect in nano scale p-MTJs induced by Joule heating. Experimental results show a sign change of the thermovoltage between different magnetic states, indicating the significant dependence of the Seebeck effect on the magnetic state of the p-MTJ. The efficiency of energy re-use can be improved by optimizing the non-magnetic layers.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2022)
Article
Engineering, Electrical & Electronic
Junlin Wang, Guanqi Li, Bosen Zhang, Kunpeng Zhang, Kaiyu Tong, Bo Liu, Hao Meng, Jing Wu, Yongbing Xu
Summary: In this study, the influence of interface edge defects on the critical current and switching time in a CoFeB MRAM device was investigated by atomistic spin model simulations. The results showed that the effect of interface edge defects depends on the thickness of the magnetic layer, the operating temperature, and the driven current density. This finding can contribute to the control of fabrication processes in STT-based technologies.
IEEE TRANSACTIONS ON MAGNETICS
(2023)
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
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
Engineering, Electrical & Electronic
K. Nishioka, S. Miura, H. Honjo, H. Naganuma, T. V. A. Nguyen, T. Watanabe, S. Ikeda, T. Endoh
Summary: The effect of magnetic coupling on the thermal stability factor Delta in magnetic tunnel junctions (MTJs) was investigated. It was found that increasing the energy constant J(cpl) of magnetic coupling can enhance Delta, but saturates when J(cpl) exceeds a critical value J(cpl_c). The magnetic static coupling constant J(stat) was much smaller than J(cpl_c), and an interlayer exchange coupling constant J(ex_c) is required to cover the difference between J(cpl_c) and J(stat). Experimental results were in good agreement with calculations, showing that Delta can be enhanced by adjusting the stiffness constant As.
IEEE TRANSACTIONS ON MAGNETICS
(2022)
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
Materials Science, Multidisciplinary
A. K. Dhiman, T. Dohi, W. Dobrogowski, Z. Kurant, I Sveklo, S. Fukami, H. Ohno, A. Maziewski
Summary: Magnetization processes and magnetic domain structures in Ta/CoFeB/MgO stacks were studied, showing a magnetization reorientation from out-of-plane to in-plane as the CoFeB thickness increased. The thickness dependence of magnetic anisotropy and the identification of an easy-cone magnetization region were important findings in the study.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(2021)
Article
Chemistry, Physical
Y. Q. Guo, H. Bai, Q. R. Cui, L. M. Wang, Y. C. Zhao, X. Z. Zhan, T. Zhu, H. X. Yang, Y. Gao, C. Q. Hu, S. P. Shen, C. L. He, S. G. Wang
Summary: The effect of vacuum annealing on the perpendicular magnetic anisotropy of MgO/CoFeB/VV stacks was studied, showing that the PMA can be well maintained at 590 degrees C. Furthermore, there was significant segregation of Co and Fe atoms at the CoFeB/W interface after annealing at this temperature.
APPLIED SURFACE SCIENCE
(2021)
Article
Physics, Applied
Hiroki Matsumoto, Shinya Ota, Tomohiro Koyama, Daichi Chiba
Summary: Researchers have fabricated a spin valve structure with a Pd/Co-based film and demonstrated a controllable spin reorientation transition by applying strain, resulting in a drastic change in the magnetoresistance curve.
APPLIED PHYSICS EXPRESS
(2022)
Article
Physics, Applied
K. Saito, A. Imai, S. Ota, T. Koyama, A. Ando, D. Chiba
Summary: This study demonstrates the considerable potential of a CoFeB/MgO-based magnetic tunnel junction (MTJ) directly formed on a flexible substrate as a high-sensitivity strain gauge. Under the condition of external magnetic-field assistance, the flexible MTJ achieves a gauge factor of approximately 1000, which is the highest sensitivity reported for a film-type strain gauge and about 500 times larger than that of the most prevalent metal-foil strain gauge. Moreover, using a flexible MTJ with strain-insensitive and strain-sensitive layers, a large resistance change due to strain application can be achieved even without the presence of a magnetic field.
APPLIED PHYSICS LETTERS
(2022)
Article
Instruments & Instrumentation
Tomonori Arakawa, Yoichi Shiota, Keisuke Yamada, Teruo Ono, Seitaro Kon
Summary: The paper presents a method for obtaining wideband magnetic polarization selective spectra of magnetic thin films using circularly polarized microwaves. The method combines an over-coupled crossed microstrip resonator and a hybrid coupler for accurate control of circularly polarized microwaves. The performance of the method is demonstrated with an yttrium iron garnet thin film, and the polarization dependence of Kittel mode and perpendicular standing spin wave mode is detected in the range of 3-20 GHz.
REVIEW OF SCIENTIFIC INSTRUMENTS
(2022)
Article
Multidisciplinary Sciences
Miguel Romera, Philippe Talatchian, Sumito Tsunegi, Kay Yakushiji, Akio Fukushima, Hitoshi Kubota, Shinji Yuasa, Vincent Cros, Paolo Bortolotti, Maxence Ernoult, Damien Querlioz, Julie Grollier
Summary: The study demonstrates the potential of spin-torque nano-oscillators in neuromorphic computing by showing their ability to mutually synchronize and recognize temporal patterns, similar to neurons. This research is important for the construction of neural networks that perform brain-inspired computations by utilizing the non-linear dynamic properties of their components.
NATURE COMMUNICATIONS
(2022)
Article
Materials Science, Multidisciplinary
Takayuki Nozaki, Tomohiro Nozaki, Tatsuya Yamamoto, Makoto Konoto, Atsushi Sugihara, Kay Yakushiji, Hitoshi Kubota, Akio Fukushima, Shinji Yuasa
Summary: Perpendicular magnetic anisotropy (PMA) is becoming increasingly important in spintronics research, especially for high-density magnetoresistive random access memories (MRAMs). This study proposes inserting an ultrathin LiF layer at the Fe/MgO interface and achieves a large intrinsic interface PMA energy. It is also found that a coherent spin-dependent tunneling process is maintained in the ultrathin LiF layer, leading to a large tunnel magnetoresistance (TMR) effect. Atomic-scale interface engineering using fluoride can further improve the PMA and TMR properties of spintronic devices.
NPG ASIA MATERIALS
(2022)
Article
Physics, Applied
T. Koyama, Y. Nakatani, D. Chiba
Summary: In this study, a Pt/Co/MgO system with regions exhibiting different anisotropy was artificially created to investigate the chirality-induced EMF at the PM/IM boundary. The EMF in the IM region was probed using magnetoresistance measurements, revealing that it predominantly acts on the magnetization near the PM/IM boundary. The sign and magnitude of the observed EMF suggest that it is caused by iDMI in the present system.
APPLIED PHYSICS LETTERS
(2022)
Article
Physics, Applied
Tomohiro Ichinose, Tatsuya Yamamoto, Jun Uzuhashi, Takayuki Nozaki, Tadakatsu Ohkubo, Kay Yakushiji, Shingo Tamaru, Kazuhiro Hono, Shinji Yuasa
Summary: Thermally robust perpendicular magnetic anisotropy and voltage-controlled magnetic anisotropy effects were achieved in magnetic tunnel junctions with ultrathin CoFeB films by utilizing Ta/Mo layered adhesion structures.
JOURNAL OF APPLIED PHYSICS
(2022)
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
Physics, Multidisciplinary
Tomonori Arakawa, Takashi Oka, Seitaro Kon, Yasuhiro Niimi
Summary: The dynamical conductivity of a system can provide microscopic information about the dissipative and nondissipative processes induced by ac-electric fields. In this study, a noncontact method using a circular cavity resonator is established to measure the real and imaginary parts of longitudinal and Hall conductivities at a microwave frequency in magnetic fields. The results reveal the presence of conventional Shubnikov-de Haas oscillations in the real part of longitudinal conductivity and quantum Hall plateaus in the real part of Hall conductivity. The periodic structures observed in the imaginary part are attributed to intra-Landau level transitions between different orbital angular momenta.
PHYSICAL REVIEW LETTERS
(2022)
Article
Physics, Applied
Yoichi Shiota, Tomonori Arakawa, Ryusuke Hisatomi, Takahiro Moriyama, Teruo Ono
Summary: In this study, the polarization-selective spectra of magnetic resonance in perpendicularly magnetized synthetic antiferromagnets were experimentally measured using a wideband crossed microstrip circuit. The magnetic resonances with different precession modes were observed, and the measurement results were explained by theoretical analysis and numerical simulations. It was also shown that magnetic excitations with different polarization types can be excited.
PHYSICAL REVIEW APPLIED
(2022)
Article
Nanoscience & Nanotechnology
Takayuki Nozaki, Tomohiro Nozaki, Hiroshige Onoda, Hiroyasu Nakayama, Tomohiro Ichinose, Tatsuya Yamamoto, Makoto Konoto, Shinji Yuasa
Summary: This study investigates the effects of inserting a post-oxidized MgAl layer on the perpendicular magnetic anisotropy (PMA), tunnel magnetoresistance (TMR), and voltage-controlled magnetic anisotropy (VCMA) in epitaxial magnetic tunnel junctions (MTJs). The results show that the thickness of the MgAl layer plays a significant role in determining PMA and TMR values. A proper thickness of the MgAl layer can greatly enhance these properties. Furthermore, the VCMA coefficient increases as the MgAl layer thickness decreases, suggesting that a weakly oxidized interface provides a stronger VCMA effect.
Article
Physics, Applied
S. Nakaharai, T. Arakawa, A. Zulkefli, T. Iwasaki, K. Watanabe, T. Taniguchi, Y. Wakayama
Summary: As an application of cryo-CMOS technology for future quantum computing, this study explores low-frequency noise reduction in a two-dimensional system with a molybdenum disulfide channel sandwiched by hexagonal boron nitride layers. The passivation effect of boron nitride layers significantly reduces low-frequency noise, compared to directly placing the molybdenum disulfide channel on a silicon dioxide substrate and silicon devices. This indicates that the clean interface and protected surface contribute to the strong reduction in noise, making 2D materials suitable for cryo-CMOS technology.
APPLIED PHYSICS LETTERS
(2023)
Article
Engineering, Electrical & Electronic
Tomonori Arakawa, Toshiyuki Igarashi, Masahiro Horibe, Shingo Tamaru, Shigeyoshi Yoshida
Summary: To support the development of smart technology, higher frequencies will be used in 5G and beyond mobile communication systems for the Internet of Things, smart devices, and smart manufacturing. This will lead to an increase in the number and types of network devices and the need to suppress electromagnetic interference in small wireless communication terminals. A noise suppression sheet is developed to minimize electromagnetic interference in the new frequency bands, and a method is created to evaluate its transmission attenuation characteristics up to 60 GHz. The practicality of the sheet is confirmed through measurements of commercially available noise suppression sheets.
IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY
(2023)
Article
Physics, Multidisciplinary
Sadashige Matsuo, Takaya Imoto, Tomohiro Yokoyama, Yosuke Sato, Tyler Lindemann, Sergei Gronin, Geoffrey C. Gardner, Michael J. Manfra, Seigo Tarucha
Summary: The behaviour of a superconductor can be modified by changing its symmetry properties, specifically by breaking time-reversal and inversion symmetries through coupling Josephson junctions. Such devices can exhibit exotic phenomena, like the controllable superconducting diode effect, which enables lossless rectification. In this study, a device consisting of two coupled Josephson junctions demonstrates the superconducting diode effect, with control based on the phase difference of the adjacent junction. This breakthrough indicates the breaking of time-reversal and spatial-inversion symmetries in Josephson junctions, allowing for engineering of superconducting phenomena mediated by interaction among Josephson junctions.
Article
Engineering, Electrical & Electronic
Tomonori Arakawa, Seitaro Kon
Summary: This paper reports a calibrated microwave measurement method for accurately evaluating the scattering parameters of cryogenic microwave components over a wide temperature range. By using 3.5-mm connectors as reference planes, various components up to 26.5 GHz can be measured with precision.
IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT
(2023)
