Yari Ferrante | Searcharxiv

arXiv2024

Ferrimagnetic Heusler tunnel junctions with fast spin-transfer torque switching enabled by low magnetization

Magnetic random access memory that uses magnetic tunnel junction memory cells is a high performance, non-volatile memory technology that goes beyond traditional charge-based memories. Today its speed is limited by the high magnetization of the memory storage layer. Here we show that fast and highly reliable switching is possible using a very low magnetization ferrimagnetic Heusler alloy, Mn3Ge. Moreover, the tunneling magnetoresistance is the highest yet achieved for a ferrimagnetic material at ambient temperature. Furthermore, the devices were prepared on technologically relevant amorphous substrates using a novel combination of a nitride seed layer and a chemical templating layer. These results show a clear path to the lowering of switching currents using ferrimagnetic Heusler materials and, therefore, to the scaling of high performance magnetic random access memories beyond those nodes possible with ferromagnetic devices.

cond-mat.mtrl-sci↗

arXiv2019

Current-Induced magnetization switching by the high spin Hall conductivity $\alpha$-W

The spin Hall effect originating from 5d heavy transition metal thin films such as Pt, Ta, and W is able to generate efficient spin-orbit torques that can switch adjacent magnetic layers. This mechanism can serve as an alternative to conventional spin-transfer torque for controlling next-generation magnetic memories. Among all 5d transition metals, W in its resistive amorphous phase typically shows the largest spin-orbit torque efficiency ~ 0.20-0.50. In contrast, its conductive and crystalline $\alpha$ phase possesses a significantly smaller efficiency ~ 0.03 and no spin-orbit torque switching has yet been realized using $\alpha$-W thin films as the spin Hall source. In this work, through a comprehensive study of high quality W/CoFeB/MgO and the reversed MgO/CoFeB/W magnetic heterostructures, we show that although amorphous-W has a greater spin-orbit torque efficiency, the spin Hall conductivity of $\alpha$-W ($|\sigma_{\operatorname{SH}}^{\alpha\operatorname{-W}}|=3.71\times10^{5}\operatorname{\Omega}^{-1}\operatorname{m}^{-1}$) is ~3.5 times larger than that of amorphous-W ($|\sigma_{\operatorname{SH}}^{\operatorname{amorphous-W}}|=1.05\times10^{5}\operatorname{\Omega}^{-1}\operatorname{m}^{-1}$). Moreover, we demonstrate spin-orbit torque driven magnetization switching using a MgO/CoFeB/$\alpha$-W heterostructure. Our findings suggest that the conductive and high spin Hall conductivity $\alpha$-W can be a potential candidate for future low power consumption spin-orbit torque memory applications.

cond-mat.mtrl-sci↗