First-principles insights into all-optical spin switching in the half-metallic Heusler ferrimagnet Mn$_2$RuGa

Abstract

All-optical spin switching (AOS) represents a new frontier in magnetic storage technologyspin 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(4a) serves as the spin anchor site, whose band structure is below the Fermi level and has a strong spin moment, while Mn(4c) 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-4d and Ga-4p 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 the future applications. Specifically, we propose a Mn 2 Ru x Ga-based magnetic tunnel junction where a single laser pulse can control magnetoresistance.