Article
Engineering, Electrical & Electronic
Jyotirmoy Chatterjee, Paulo Coelho, Antoine Chavent, Ricardo C. Sousa, Stephane Auffret, Claire Baraduc, Ioan-Lucian Prejbeanu, Bernard Dieny
Summary: In this study, a novel class of hard and out-of-plane magnetized seedless multilayers consisting of [Co/insertion layer/Pt](n) was investigated for potential applications as top reference layers in magnetic tunnel junctions (MTJ). Among various nonferrous insertion layers tested, Ta was found to exhibit the highest perpendicular magnetic anisotropy. By using Ta-inserted SL-MLs, a back-end-of-line (BEOL) compatible top reference layer with more than double the effective perpendicular anisotropy of a conventional top reference layer was achieved. Three types of spintronic memory stacks were developed using this top reference layer, each with unique features and capabilities, such as the ability to withstand high-temperature annealing, faster readout and low-voltage writing, and combining different writing techniques for increased efficiency.
ACS APPLIED ELECTRONIC MATERIALS
(2021)
Article
Engineering, Electrical & Electronic
Hugo Nicolas, Ricardo C. Sousa, Ariam Mora-Hernandez, Ioan-Lucian Prejbeanu, Luc Hebrard, Jean-Baptiste Kammerer, Joris Pascal
Summary: This article presents a new type of magnetic sensor using a perpendicular spin transfer torque magnetic tunnel junction (MTJ). The sensor has a cylindrical shape with a diameter of 50 nm, making it one of the smallest magnetic sensors reported. The article discusses the principle of operation, signal processing electronics, experimental results, and comparisons to existing magnetic sensors. The sensor demonstrates high sensitivity and dynamic range, and its compatibility with standard microelectronics components allows for integration with conditioning electronics.
IEEE SENSORS JOURNAL
(2023)
Article
Engineering, Electrical & Electronic
Hugo Nicolas, Ricardo C. Sousa, Ariam Mora-Hernandez, Ioan-Lucian Prejbeanu, Luc Hebrard, Jean-Baptiste Kammerer, Joris Pascal
Summary: This article presents a new type of magnetic sensor using a perpendicular spin transfer torque magnetic tunnel junction (MTJ). The sensor has a cylindrical shape with a diameter of 50 nm, making it one of the smallest ever reported. The article describes the principle of operation, signal processing electronics, and compares its performance with commercially available sensors. The developed sensor has a sensitivity of 1.28 V/T, a dynamic range of 80 mT, and a noise level of 21.8 μT/√Hz. The sensor and its electronics are compatible with existing fabrication processes, allowing for mass production in various markets.
IEEE SENSORS JOURNAL
(2023)
Article
Engineering, Electrical & Electronic
Santiago S. Perez, Alessandro Bedoya, Luis Miguel Procel, Ramiro Taco
Summary: This study utilizes double-barrier magnetic tunnel junction (DMTJ) technology to define STT-MRAM at the circuit level. The results indicate that the tunnel-FET based solution is the most energy-efficient alternative with lower leakage current.
INTERNATIONAL JOURNAL OF APPLIED ELECTROMAGNETICS AND MECHANICS
(2023)
Article
Physics, Multidisciplinary
Qiuyang Li, Penghe Zhang, Haotian Li, Lina Chen, Kaiyuan Zhou, Chunjie Yan, Liyuan Li, Yongbing Xu, Weixin Zhang, Bo Liu, Hao Meng, Ronghua Liu, Youwei Du
Summary: Through experiments and simulations, it has been found that perpendicular anisotropy magnetic tunnel junctions (pMTJs) exhibit fast switching times and low write energies, and the switching time can be further reduced when the perpendicular magnetic anisotropy and damping constant of the free layer are lower within a certain range.
Article
Engineering, Electrical & Electronic
Abdolah Amirany, Kian Jafari, Mohammad Hossein Moaiyeri
Summary: This article introduces a DDR-MRAM with the aim of reducing switching delay, area overhead, and power consumption in MTJ-based memories. Simulation results and Monte-Carlo simulations validate the performance and stability of DDR-MRAM. Three DDR-MRAM array architectures optimized for specific applications are proposed.
IEEE TRANSACTIONS ON MAGNETICS
(2022)
Article
Engineering, Electrical & Electronic
M. Niwa, K. Kimura, T. Naijo, A. Oshurahunov, S. Nagamachi, H. Inoue, H. Honjo, S. Ikeda, T. Endoh
Summary: The study successfully observed the microstructure of nano-scale CoFeB-MgO-based magnetic tunnel junctions, identified the root cause of resistance changes, determined the composition of the altered region inside the MTJ, and confirmed the effectiveness of STEM tomography in failure analysis.
IEEE TRANSACTIONS ON MAGNETICS
(2021)
Article
Engineering, Electrical & Electronic
Zhitai Yu, Yijiao Wang, Zeqing Zhang, Kuiqing He, Lang Zeng, Zhaohao Wang, Weisheng Zhao
Summary: This paper introduces a Two-bits-cell based NAND-Like MRAM device, which reduces area overhead and improves data storage efficiency through stacking cells and NAND-Like structure, and achieves low power consumption, low latency, and field-free switching with a toggle-like writing scheme. The proposed structure also shows potential for application in a multifunctional sensing circuit in memory computing systems.
IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS II-EXPRESS BRIEFS
(2021)
Article
Computer Science, Information Systems
Gulafshan Gulafshan, Selma Amara, Rajat Kumar, Danial Khan, Hossein Fariborzi, Yehia Massoud
Summary: Today's technology requires devices that are compact, portable, fast, and energy-efficient. This paper presents a circuit design based on voltage-controlled magnetic anisotropy magnetoresistive random access memory (VCMA-MRAM), which utilizes logic-in-memory computing paradigm and approximate computation to address the memory bottleneck issues in the present computing system. Simulation results demonstrate that the proposed circuit's approximate adder consumes about 300% less energy and is 2.3 times faster than its exact counterpart.
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
Engineering, Electrical & Electronic
T. Patrick Xiao, Christopher H. Bennett, Frederick B. Mancoff, Jack E. Manuel, David R. Hughart, Robin B. Jacobs-Gedrim, Edward S. Bielejec, Gyorgy Vizkelethy, Jijun Sun, Sanjeev Aggarwal, Reza Arghavani, Matthew J. Marinella
Summary: The study evaluated the resilience of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) with perpendicular magnetic anisotropy (PMA) to displacement damage induced by heavy-ion irradiation. It found that damage to the MgO interfaces led to a decrease in magnetoresistance and PMA, elucidating the thresholds for significant irreversible changes in the characteristics of STT-MRAM devices.
IEEE TRANSACTIONS ON NUCLEAR SCIENCE
(2021)
Article
Green & Sustainable Science & Technology
A. Palomino, J. Marty, S. Auffret, I. Joumard, R. C. Sousa, I. L. Prejbeanu, B. Ageron, B. Dieny
Summary: STT-MRAM, with its unique combination of properties, is expected to play a key role in IoT and information communication technologies. Recent studies have focused on critical materials in magnetic random access memory, with potential significant reductions in energy requirements and global warming potential by substituting Co/Pt multilayers.
SUSTAINABLE MATERIALS AND TECHNOLOGIES
(2021)
Article
Engineering, Electrical & Electronic
Debasis Das, Xuanyao Fong
Summary: Embedded nonvolatile memory technologies, such as RRAM and STT MRAM, are being increasingly studied for neuromorphic computing and AI hardware accelerators. A proposed approach using the Fokker-Planck equation can model the stochastic write processes in these devices and reproduce experimental results.
IEEE TRANSACTIONS ON ELECTRON DEVICES
(2021)
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
Engineering, Electrical & Electronic
Manoj Kumar Yadav, Santosh Kumar Gupta
Summary: This study presents a first principle analysis of Fe/MgO/Fe magnetic tunnel junctions (MTJ) with gate voltage control over the insulated barrier region. The results show that the different work functions of the gate and barrier materials lead to the transfer of density of states (DOS) in the forbidden energy gap of MgO due to the Schottky effect. The high spin injection efficiency and tunnel magneto resistance (TMR) ratios observed in this study indicate the potential of MTJs as three-terminal devices for magnetic random access memory (MRAM) applications.
IEEE TRANSACTIONS ON ELECTRON DEVICES
(2022)
Article
Physics, Applied
Kresna B. Fathoni, Yuya Sakuraba, Yoshio Miura, Taisuke Sasaki, Tomoya Nakatani, Kazuhiro Hono
Summary: The study indicates that in order to enhance the magnetoresistance ratio in CIP-GMR using half-metallic materials, it is crucial to match the resistivity between the ferromagnetic layers and the nonmagnetic layer, in addition to considering the high electronic band matching as a key factor to achieve high MR ratio in CIP-GMR devices.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2022)
Editorial Material
Materials Science, Multidisciplinary
Satoshi Hirosawa, Kazuhiro Hono
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS
(2022)
Article
Nanoscience & Nanotechnology
Ruma Mandal, Ivan Kurniawan, Ippei Suzuki, Zhenchao Wen, Yoshio Miura, Takahide Kubota, Koki Takanashi, Tadakatsu Ohkubo, Kazuhiro Hono, Yukiko K. Takahashi
Summary: In this study, a high-quality half-metallic epitaxial nano-scale thick NiMnSb alloy film grown on a Cr/Ag-buffered MgO (001) single crystalline substrate was reported. The highly ordered C1(b) structured nano-scale thick NiMnSb film deposited at 573 K exhibited ultralow Gilbert damping, high anisotropic field, and saturation magnetization. The analysis of theoretical and experimental data revealed a strong correlation between crystal ordering and magnetic parameters, as well as sample quality. The negative anisotropic magnetoresistance ratio demonstrated the robust bulk half-metallicity. This unique combination of highly ordered nano-scale half-metallic NiMnSb alloy with ultralow damping can be advantageous for spintronic device applications.
ACS APPLIED NANO MATERIALS
(2022)
Article
Materials Science, Multidisciplinary
A. Bolyachkin, H. Sepehri-Amin, M. Kambayashi, Y. Mori, T. Ohkubo, Y. K. Takahashi, T. Shima, K. Hono
Summary: In this study, the effect of microstructural factors on coercivity was investigated, and it was found that the coercivity of SmFe12-based compounds can be improved by grain boundary diffusion of Si. Detailed microstructure characterization confirmed the diffusion of Si in the intergranular phase and the reduction of Fe and Co content. However, the presence of α-(Fe,Co) grains at the interface reduced the effectiveness of grain boundary diffusion. Therefore, high coercivity in SmFe12-type magnets can only be achieved by eliminating the α-(Fe,Co) phases.
Article
Materials Science, Multidisciplinary
Jiawei Lai, A. Bolyachkin, N. Terada, S. Dieb, Xin Tang, T. Ohkubo, H. Sepehri-Amin, K. Hono
Summary: Fe2P-type compounds exhibit a giant magnetocaloric effect and are studied for room temperature applications. In this study, rare-earth-free compounds with cryogenic magnetocaloric effect were optimized using data mining and machine learning, demonstrating promising magnetocaloric performance.
Article
Physics, Applied
Pelin Tozman, Hossein Sepehri-Amin, Xin Tang, Tadakatsu Ohkubo, Kazuhiro Hono
Summary: Substitution of Co for Fe in SmFe12-based compounds realizes large saturation magnetization. This study successfully reduces the concentration of Co while maintaining a large magnetic moment in the compound. Additionally, (Sm0.8Y0.2)Fe12-based compounds exhibit superior magnetic properties compared to Nd2Fe14B.
APPLIED PHYSICS EXPRESS
(2022)
Article
Materials Science, Multidisciplinary
Kresna B. Fathoni, Zehao Li, Tomoya Nakatani, Yuya Sakuraba, Taisuke Sasaki, Kazuhiro Hono
Summary: The MR ratio of CoFe/bcc-Cu/CoFe CIP-GMR devices grown on Si(0 0 1) substrate is slightly lower than that grown on MgO(0 0 1) substrate due to the presence of fcc phase of Cu.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(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
Nanoscience & Nanotechnology
Kazuho Okada, Akinobu Shibata, Taisuke Sasaki, Hisashi Matsumiya, Kazuhiro Hono, Nobuhiro Tsuji
Summary: This study aimed to improve the resistance against hydrogen embrittlement by increasing the concentration of carbon segregated at prior austenite grain boundary (PAGB), XPAGB, in low-carbon martensitic steels. The specimens with and without carbon segregation treatment (Non-seg and Seg specimens, respectively) had similar microstructures, except for higher XPAGB in the Seg specimen. The Seg specimen exhibited higher maximum stress and smaller fraction of intergranular fracture surface under hydrogen-charged conditions, indicating that segregated carbon suppressed hydrogen accumulation and increased cohesive energy of PAGB.
SCRIPTA MATERIALIA
(2023)
Article
Physics, Applied
Zixi Chen, Yuya Sakuraba, Yoshio Miura, Zehao Li, Taisuke Sasaki, Hirofumi Suto, Varun K. Kushwaha, Tomoya Nakatani, Seiji Mitani, Kazuhiro Hono
Summary: This study investigates the effects of off-stoichiometric compositional variations on the electronic structure of the Co2Fe(Ga0.5Ge0.5) full-Heusler alloy. First-principles calculations predict that Co-Fe defects introduce a finite density of states in the half-metallic gap, while Fe-Co defects preserve the gap but reduce spin polarization. Experimental results confirm that Ge-excess in Fe-excess CFGG enhances spin polarization. By adjusting the Fe and Ge compositions, the formation of secondary phases can be suppressed.
JOURNAL OF APPLIED PHYSICS
(2022)
Article
Nanoscience & Nanotechnology
Z. H. Li, S. Gao, T. T. Sasaki, T. Nakata, S. Kamado, N. Tsuji, K. Hono
Summary: Clarifying the origin of the yielding phenomenon is crucial for improving the flow stability and surface finish of magnesium alloy sheet products. This study investigates the effect of Zn addition on discontinuous yielding in low-alloyed magnesium alloy sheets and reveals the significant impact of Zn on yield-drop. Transmission electron microscopy and atom probe tomography analysis demonstrate the influence of Ca-Zn co-clusters on dislocations, and different stretching directions of the sheet result in distinct Luders deformations.
SCRIPTA MATERIALIA
(2022)
Article
Microscopy
Sujin Lee, Atsuko Sato, Takehiro Tamaoka, Kunio Yubuta, Mitsunari Auchi, Taisuke Sasaki, Tadakatsu Ohkubo, Kazuhiro Hono, Yasukazu Murakami
Summary: This paper proposes a method using electron holography to provide a phase image of the demagnetization field (H-d) within a thin-foil permanent magnet. The observation of H-d remains challenging because electron holography can only image the magnetic flux density (B), which is a combination of contributions from magnetization (M), stray magnetic field (H-s) outside the specimen, and H-d inside the specimen. The phase map approximating H-d, determined from electron holography observation of a Nd2Fe14B single-crystalline specimen, shows good agreement with micromagnetic theory's prediction. This method can be applied to study the coercivity mechanism of permanent magnets, which is sensitive to the demagnetization field.
Article
Materials Science, Multidisciplinary
Z. Wang, T. T. Sasaki, Y. Une, T. Ohkubo, K. Hono
Summary: Record-breaking high coercivity is achieved in Dy-free sintered magnets by separately diffusing Dy70Cu30 and Pr68Cu32 eutectic alloys. The low Dy content sample exhibits a high coercivity of 2.8 T and an excellent temperature coefficient of coercivity. The unique presence of a uniform Dy-rich shell and enriched Pr near the surface of Nd2Fe14B grains strengthens the anisotropy field, resulting in the high coercivity without alloying Dy to the initial magnet.
Article
Chemistry, Physical
Z. H. Kautsar, H. Sepehri-Amin, Xin Tang, R. Iguchi, K. Uchida, T. Ohkubo, K. Hono
Summary: The resistivities of anisotropic Nd-Fe-B-based magnets were increased in parallel and perpendicular directions to the c-axis by hot-deforming Nd-Fe-B melt-spun flakes coated with DyF3 through electrophoretic deposition. As a result, the operating temperature under high-frequency AC magnetic field decreased by 20°C due to the reduction of eddy current loss. The formation of a resistive layer composed of NdF3 at the interface of original ribbons in the hot-deformed magnet was observed. The excess Dy diffused into the original ribbon flakes and formed a Dy-rich shell in Nd2Fe14B grains, resulting in a high coercivity.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Microscopy
Jun Uzuhashi, Tadakatsu Ohkubo, Kazuhiro Hono
Summary: Atom probe tomography (APT) is a widely used technique for analyzing the microstructure of alloys and devices. In this study, a method for automatically fabricating the desired tip shape using a script-controlled FIB-SEM system was developed. The effect of intentionally changing the tip shape on APT data was also discussed.