Enhancement of room-temperature unidirectional spin Hall magnetoresistance by using a ferromagnetic metal with a low Curie temperature

The unidirectional spin Hall magnetoresistance (USMR) effect is useful to detect the direction of magnetiza-tion in a ferromagnetic metal/nonmagnetic metal bilayer, which is the typical geometry used in a spin-orbit torque switching device. In this Letter, we demonstrate the enhancement of the USMR effect by reducing the Curie temperature TC of the ferromagnetic (FM) layer in a FM/platinum bilayer. The USMR ratio was maximized when the thickness of each FM layer was consistent with the spin diffusion length. We found that the maximum USMR ratio can be doubled by replacing Ni81Fe19 (TC = 854 K) with Ni85Cu15 (TC = 527 K) as the FM. This enhancement of the USMR effect is attributed to an increase of electron-magnon scattering in accordance with Bloch law. We also found that the use of ferromagnets with face-centered-cubic structures, such as Ni, Ni81Fe19, and Ni85Cu15, increased the USMR effect relative to that of body-centered-cubic Fe.

Automated summary

This Letter demonstrates the enhancement of the unidirectional spin Hall magnetoresistance (USMR) effect by reducing the Curie temperature TC of the ferromagnetic (FM) layer in a FM/platinum bilayer. The USMR ratio is maximized when the thickness of each FM layer is consistent with the spin diffusion length. By replacing Ni81Fe19 with Ni85Cu15 as the FM material, the maximum USMR ratio can be doubled. This enhancement of the USMR effect is attributed to an increase of electron-magnon scattering in accordance with Bloch law. The use of ferromagnets with face-centered-cubic structures, such as Ni, Ni81Fe19, and Ni85Cu15, increases the USMR effect compared to body-centered-cubic Fe.