First-principles insight into all-optical spin switching in the half-metallic Heusler ferrimagnet ${\mathrm{Mn}}_{2}\mathrm{RuGa}$

First-principles insight into all-optical spin switching in the half-metallic Heusler ferrimagnet ${Mn}_{2} RuGa$

G. P. Zhang, Y. H. Bai, M. S. Si, and Thomas F. George

Phys. Rev. B 105, 054431 – Published 25 February 2022

Abstract

All-optical spin switching (AOS) represents a new frontier in magnetic storage technology—spin manipulation without a magnetic field—but its underlying working principle is not well understood. Many AOS ferrimagnets such as GdFeCo are amorphous and renders the high-level first-principles study unfeasible. The crystalline half-metallic Heusler ${Mn}_{2} RuGa$ presents an opportunity. Here we carry out hitherto the comprehensive density functional investigation into the material properties of ${Mn}_{2} RuGa$ , and introduce two concepts—the spin anchor site and the optical active site—as two pillars for AOS in ferrimagnets. In ${Mn}_{2} RuGa, Mn (4 a)$ serves as the spin anchor site, whose band is below the Fermi level and has a strong spin moment, while $Mn (4 c)$ is the optical active site whose band crosses the Fermi level. Our magneto-optical Kerr spectrum and band structure calculation jointly reveal that the delicate competition between the Ru- $4 d$ and Ga- $4 p$ states is responsible for the creation of these two sites. These two sites found here not only present a unified picture for both ${Mn}_{2} RuGa$ and GdFeCo, but also open the door for future applications. Specifically, we propose a ${Mn}_{2} {Ru}_{x} Ga-based$ magnetic tunnel junction where a single laser pulse can control magnetoresistance.