The T-shaped spin conversion device consisting of ferromagnetic and spin Hall (or spin conversion) materials is an indispensable component in a new type of logic circuit: magnetoelectric spin-orbit logic circuit. In this device, a spin polarized current is directly injected into the spin Hall material from the ferromagnet, and the inverse spin Hall effect (ISHE) is detected as the transverse voltage as shown in Fig. 1 (a). The output signal can be an order of magnitude greater than that of the nonlocal methods. Pham et al. have demonstrated an increase in the ISHE signal by scaling down the T-shaped device structure, that is favorable for the high-density device [1]. They also discussed the adverse effects of the adjacent ferromagnet on the total signal via a transverse anisotropic magnetoresistance, the planar Hall effect (PHE), concluding that it only causes the offset of the output signal. However, our recent experiments showed the superposition of the signal induced by PHE which change its sign upon magnetization reversal.

Fig. 1. (a) Schematic of ISHE measurement in the T-shaped spin conversion device. (b) Magnetic field dependence of the transverse resistance R_xy in the Pt/FeNi device with θ = 0°. Red and blue arrows show the magnetic field sweeping direction. (c), (d) asymmetric and symmetric components of R_xy. (e), (f) Magnetic field angle dependences of the asymmetrical and symmetrical components H = 0.8 T.

In this work, we investigated the influence of PHE on the ISHE induced voltage on the T-shaped device. The T-shaped Pt wires were first formed on the Si/SiO₂ substrate using e-beam lithography, e-beam deposition, and liftoff. The thickness of Pt is 20 nm. We then deposited a ferromagnetic wire on the Pt. Figure 2(b) shows the magnetic field dependence of R_xy in the Pt/FeNi device. One can extract the asymmetric contribution in R_xy by calculating the difference between the signals measured at trace and retrace scan. Figures 1(c) and (d) show asymmetric and symmetric components as a function of the applied field, respectively. Figure 1 (e) and (f) show the magnetic field angle dependences of the symmetric and symmetric components, respectively. The ISHE causes an asymmetric component of the transverse resistance in the T-shaped device structure. On the other hand, we found that the PHE contributes to the transverse voltage as a symmetric component because the magnetic moment continuously rotates clockwise (or counterclockwise). From the experimental results, the spin Hall angle of Pt and the anisotropic magnetoresistance ratio of FeNi were estimated to be ~ 3.0% and ~ 1.0%, respectively, that are in the same order as the reported value. We did same measurement on a Pt/CoFe device. The overall change in the asymmetric component is almost the same as that in the Pt/FeNi, while the change in the symmetric component is about half of that in the Pt/FeNi device. This reduction of the symmetric signal is attributed to the lower anisotropic magnetoresistance ratio of CoFe than that of FeNi. Therefore, it is essential to use the ferromagnet that has small anisotropic magnetoresistance ratio to reduce the adverse effect in the T-shaped device.

In conclusion, our systematic studies reveal that the PHE causes a symmetric component in the output signal because of the continuous clockwise (or counterclockwise) magnetic rotation. We find that we can suppress the undesired signal by choosing a low AMR ferromagnet such as the CoFe alloy. These results help us to design the T-shaped device structure for studying spin conversion in spin Hall materials, topological insulators, and Rashba interface for developing the spintronic logic devices.

References

• [1] V. T. Pham, I. Groen, S. Manipatruni, W. Y. Choi, D. E. Nikonov, E. Sagasta, C.-C. Lin, T. A. Gosavi, A. Marty, L. E. Hueso, I. A. Young, and F. Casanova, Nat. Electron. 3, 309 (2020)
• [2] H. Mizuno, H. Isshiki, K. Kondou, Y. Zhu, and Y. Otani, Appl. Phys. Lett. 119, 092401 (2021)

Authors

• Y. Otani and H. Isshiki