Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
16
Scopus Publications
Scopus Publications
130-nm CMOS-integrated superparamagnetic tunnel junction-based p-bit Ju-Young Yoon, Nuno Caçoilo, Advait Madhavan, Jabez J. McClelland, Shun Kanai, Hideo Ohno, Shunsuke Fukami, William A. Borders IEEE Electron Device Letters, 2026 Probabilistic computers offer promising solutions for computationally hard problems in domains such as combinatorial optimization and machine learning. A key building block in these systems is the probabilistic bit (p-bit), which relies on superparamagnetic tunnel junctions (sMTJs) as its source of randomness. A challenging threshold to cross for scaling sMTJ-based p-bit systems is integration of sMTJs with CMOS technology. In this work, we present experimental results of a p-bit unit cell using sMTJs integrated with 130 nm CMOS technology and demonstrate that the sMTJ’s resistance fluctuations can generate a corresponding fluctuating digital output voltage which is tunable via the input voltage. These findings establish the feasibility of CMOS-compatible, sMTJ-based probabilistic circuits and mark a key step toward scalable hardware for real-world probabilistic computing applications.
Electrical mutual switching in a noncollinear-antiferromagnetic–ferromagnetic heterostructure Ju-Young Yoon, Yutaro Takeuchi, Ryota Takechi, Jiahao Han, Tomohiro Uchimura, Yuta Yamane, Shun Kanai, Jun’ichi Ieda, Hideo Ohno, Shunsuke Fukami Nature Communications, 2025 Spin-orbit torque (SOT) provides a promising mechanism for electrically encoding information in magnetic states. Unlike existing schemes, where the SOT is passively determined by the material and device structures, an active manipulation of the intrinsic SOT polarity would allow for flexibly programmable SOT devices. Achieving this requires electrical control of the current-induced spin polarization of the spin source. Here we demonstrate a proof-of-concept current-programmed SOT device. Using a noncollinear-antiferromagnetic/nonmagnetic/ferromagnetic Mn3Sn/Mo/CoFeB heterostructure at zero magnetic field, we show current-induced switching in the CoFeB layer due to the spin current polarized by the magnetic structure of the Mn3Sn; by properly tuning the driving current, the spin current from the CoFeB further reverses the magnetic orientation of the Mn3Sn, which determines the polarity of the subsequent switching of the CoFeB. This scheme of mutual switching can be achieved in a spin-valve-like simple protocol because each magnetic layer serves as a reversible spin source and target magnetic electrode. It yields intriguing proof-of-concept functionalities for unconventional logic and neuromorphic computing. Spin-orbit torque can drive switching in ferromagnets, and therefore can be used for the electrical writing of magnetic bits. Here, Yoon et al. take this essential idea a step further, demonstrating mutual switching, where a ferromagnet can drive switching in an antiferromagnet, switching the sign of the spin-orbit torque itself.
Size dependence of the properties of synthetic-antiferromagnet-based stochastic magnetic tunnel junctions for probabilistic computing Takuma Kinoshita, Ju-Young Yoon, Nuno Caçoilo, Ryota Mochizuki, Haruna Kaneko, Shun Kanai, Hideo Ohno, Shunsuke Fukami Applied Physics Letters, 2025 Stochastic magnetic tunnel junctions (s-MTJs) are core components for spintronics-based probabilistic computing, offering promising routes toward energy-efficient unconventional computing. A synthetic antiferromagnetic (SAF) free layer configuration has been proposed to enhance the robustness of these devices against external magnetic field disturbance. Here, we systematically investigate the stochastic properties of SAF-based s-MTJs, with a particular focus on their size dependence. We demonstrate that decreasing the junction size from approximately 100 nm to around 40 nm reduces the relaxation time. Importantly, smaller junctions show markedly enhanced robustness against external magnetic fields, achieving susceptibility values below 0.1 mT−1 for sizes under 80 nm. Furthermore, we observe that smaller junctions exhibit enhanced insensitivity to bias voltage, with sensitivity values of around 0.5 V−1 at device sizes of approximately 40 nm, which is 100 times lower than that of conventional s-MTJs. These quantitative results provide clear guidelines for designing robust and scalable s-MTJ devices, essential for advancing spintronic probabilistic computing toward practical implementation.
Electrical coherent driving of chiral antiferromagnet Yutaro Takeuchi, Yuma Sato, Yuta Yamane, Ju-Young Yoon, Yukinori Kanno, Tomohiro Uchimura, K. Vihanga De Zoysa, Jiahao Han, Shun Kanai, Jun’ichi Ieda, Hideo Ohno, Shunsuke Fukami Science, 2025 Electric current driving of antiferromagnetic states at radio or higher frequencies remains challenging to achieve. In this study, we report all-electrical, gigahertz-range coherent driving of chiral antiferromagnet manganese-tin (Mn 3 Sn) nanodot samples. High coherence in multiple trials and threshold current insensitive to pulse width, in contrast to results observed with ferromagnets, were achieved in subnanosecond range, allowing 1000/1000 switching by 0.1-nanosecond pulses at zero field. These features are attributed to the inertial nature of antiferromagnetic excitations. Our study highlights the potential of antiferromagnetic spintronics to combine high speed and high efficiency in magnetic device operations.
Magnetic phase diagram of Mn3+xSn1−x epitaxial thin films: Extending the anomalous Hall effect to low temperatures via intrinsic alloying K. Gas, J.-Y. Yoon, Y. Sato, H. Kubota, P. Dłużewski, S. Kret, J. Z. Domagala, Y. K. Edathumkandy, Y. Takeuchi, S. Kanai, H. Ohno, M. Sawicki, S. Fukami APL Materials, 2025 Antiferromagnets with broken time-reversal symmetry, such as Mn3Sn, have emerged as promising platforms for exploring topological and correlated electron physics. Mn3Sn is known to show two magnetic phase transitions: a non-collinear inverse triangular antiferromagnetic (IT-AFM) spin configuration is formed below its Néel temperature (TN ≅ 420 K), whereas at T1 that usually locates below room temperature, it transits to an incommensurate spin state. Accordingly, intriguing properties such as a strong anomalous Hall effect, observed from TN to T1, disappear below T1, limiting its utility at low temperatures. While bulk Mn3Sn has been extensively studied, the magnetic phase transitions and their tunability in thin films remain largely unexplored. Here, we investigate the magnetic and magneto-transport properties of Mn3+xSn1−x epitaxial thin films prepared by magnetron sputtering, systematically varying the Mn–Sn composition. Our results reveal that intrinsic alloying with Mn provides us with a handle to tune T1, with the IT-AFM phase stabilized down to liquid helium temperatures for x > 0.15. From a magnetic phase diagram for epitaxial thin films, we also find a consistent magnetic anomaly ∼55 K below TN, accompanied by thermal hysteresis. Furthermore, the reduction in TN in thin films relative to bulk values is shown to correlate with lattice parameter changes. These findings extend the accessible temperature range for Mn3Sn’s topological properties, paving the way for novel applications and further investigations into the interplay of spin, lattice, and electronic degrees of freedom in thin-film geometries.
Unconventional Spin Hall Magnetoresistance in Noncollinear Antiferromagnet/Heavy Metal Stacks Tomohiro Uchimura, Jiahao Han, Ping Tang, Ju-Young Yoon, Yutaro Takeuchi, Yuta Yamane, Shun Kanai, Gerrit E. W. Bauer, Hideo Ohno, Shunsuke Fukami Physical Review Letters, 2025 We study the spin Hall magnetoresistance (SMR) in noncollinear antiferromagnet Mn_{3}Sn/heavy-metal stacks. The measured SMR exhibits peculiar magnetic field angle and magnitude dependence that sharply deviates from the conventional SMR theory based on the dampinglike spin-transfer torque. An alternative model based on a coherent fieldlike torque reproduces the observations well. Our work reveals a previously unrecognized mechanism of interfacial exchange that indicates a precession of the conduction-electron spins in the collective local exchange fields of the noncollinear antiferromagnetic order. The unraveled physics is essential to understanding and controlling spin transport in unconventional magnetic materials.
Thermal stability of non-collinear antiferromagnetic Mn3Sn nanodot Yuma Sato, Yutaro Takeuchi, Yuta Yamane, Ju-Young Yoon, Shun Kanai, Jun’ichi Ieda, Hideo Ohno, Shunsuke Fukami Applied Physics Letters, 2023 D019-Mn3Sn, an antiferromagnet having a non-collinear spin structure in a kagome lattice, has attracted great attention owing to various intriguing properties such as large anomalous Hall effect. Stability of a magnetic state against thermal fluctuation, characterized in general by the thermal stability factor Δ, has been well studied in ferromagnetic systems but not for antiferromagnets. Here, we study Δ of the antiferromagnetic Mn3Sn nanodots as a function of their diameter D. To quantify Δ, we measure the switching probability as a function of the pulse-field amplitude and analyze the results based on a model taking account of two and sixfold magnetic anisotropies in the kagome plane. We observe no significant change in Δ down to D = 300 nm below which it decreases with D. The obtained D dependence is well explained by a single-domain and nucleation-mediated reversal models. These findings provide a basis to understand the thermal fluctuation and reversal mechanism of antiferromagnets for device applications.
