Spintronics based on ferromagnets has not only revolutionized memory technologies but also led to the development of microwave devices such as spin-torque oscillators and spin-torque diodes. These microwave spintronic devices typically operate at ferromagnetic resonance conditions, with frequencies reaching several tens of GHz. However, increasing the frequency often narrows the magnetization precession cone angle, thereby weakening the output signals. Antiferromagnets offer a promising alternative. In easy-plane antiferromagnets, when a spin current with spin polarization perpendicular to the easy plane is injected, each spin deviates out of the easy plane. Due to this deviation, the exchange interaction acts to restore the spins to the easy plane, creating an effective magnetic field. This field drives spin precession around itself, enabling operation at much higher frequencies while maintaining the precession cone angle.

In this study [1], we focused on the easy-plane non-collinear antiferromagnet Mn₃Sn. This material exhibits a strong anomalous Hall effect despite negligible magnetization, and therefore, sizeable microwave responses are expected. Recent studies have shown that spin torque can drive switching and continuous rotation—referred to as chiral spin rotation—of the non-collinear triangular spin structure. In this work, we investigate the microwave response of Mn₃Sn and demonstrate the antiferromagnetic spin-torque diode effect [1], in which the interaction between chiral spin rotation and a microwave current generates a rectified DC transverse Hall voltage.

We fabricated W/Mn₃Sn epitaxial bilayers on MgO(110) substrates using molecular beam epitaxy. Hall bar devices (Mn₃Sn: 7 nm, W: 6 nm) were patterned by standard photolithography and Ar ion etching. A DC bias current and amplitude-modulated microwave current were applied via a bias-tee, and the resulting DC Hall voltages were measured using a lock-in amplifier, as schematically shown in Fig. 1.

Figure 2 shows the observed DC Hall voltage as a function of in-plane magnetic fields under the simultaneous application of DC and microwave currents. When the DC current is lower than the threshold for initiating chiral spin rotation, the data are rather featureless. On the other hand, when the DC current exceeded the threshold, peak feature appeared at a specific magnetic field. Numerical simulations suggest that these rectification signals originate from the effective modulation of the chiral spin rotation frequency by the microwave spin-orbit torque. This antiferromagnetic spin-torque diode effect was found robust at higher frequencies, offering the potential for broadband spintronic functionality beyond the GHz limitations of ferromagnetic systems.

Reference

• [1] S. Sakamoto, T. Nomoto, T. Higo, Y. Hibino, T. Yamamoto, S. Tamaru, Y. Kotani, H. Kosaki, M. Shiga, D. Nishio-Hamane, T. Nakamura, T. Nozaki, K. Yakushiji, R. Arita, S. Nakatsuji, and S. Miwa, Nat. Nanotechnol. 20, 216-221 (2025).

Authors

• S. Sakamoto, T. Nomoto^a,b, T. Higo^a, Y. Hibino^c, T. Yamamoto^c, S. Tamaru^c, Y. Kotani^d, H. Kosaki, M. Shiga, D. Nishio-Hamane, T. Nakamura^e,d, T. Nozaki^c, K. Yakushiji^c, R. Arita^a,f, S. Nakatsuji^a,g, and S. Miwa
• ^aThe University of Tokyo
• ^bTokyo Metropolitan University
• ^cNational Institute of Advanced Industrial Science and Technology
• ^dJapan Synchrotron Radiation Research Institute
• ^eTohoku University
• ^fRIKEN
• ^gJohns Hopkins University