Magneto-Transport Properties in Co₂MnGa/(Topological Insulator Bi₂Te₃, Heavy Metal W & Pt) Based Heterostructures

The Weyl semimetal Co₂MnGa (CMG) has recently attracted significant attention in the field of condensed matter physics due to simultaneous presence of topological properties and ferromagnetism at room temperature. These remarkable characteristics make CMG an exciting candidate for spintronic applications from both a theoretical and technological standpoint. Despite its potential, studies exploring phenomena like the spin Seebeck effect and spin pumping through the inverse spin Hall effect (ISHE) in CMG remain limited. Furthermore, CMG demonstrates perpendicular magnetic anisotropy (PMA) at reduced thicknesses, offering additional potential for spintronic device development.
In this study, the spin generation, spin pumping and the efficiency of spin-to-charge conversion (SCC) is investigated from CMG into various nonmagnetic (NM) layers, including heavy metals like Pt and W, and topological materials like Bi₂Te₃, using the ISHE. Our findings highlight that Bi₂Te₃ exhibits a notably high spin Hall angle of approximately 1.5, whereas W possesses a significant spin mixing conductance of around 1.8 × 10¹⁹ m^-2 in CMG-based heterostructures. Additionally, the study establishes that interfacial spin transport efficiency is closely linked to SCC efficiency, which depends on the spin-orbit coupling strength of the NM layer and the quality of the CMG/NM interface. The anomalous Nernst coefficient for a 20 nm single layer CMG film is found to be geometry-independent (both in-plane magnetised and out-of-plane magnetised geometries), with an estimated value of 0.41 μV/K. The longitudinal spin Seebeck effect (LSSE) results align well with the ISHE measurements obtained from various CMG/NM bilayers.
In addition, the spin pumping efficiency across different CMG thicknesses is also quantitatively compared in these heterostructures of CMG with Bi₂Te₃ and W. Notably, the PMA is clearly evidenced in the CMG/BT bilayer when the CMG thickness is reduced to approximately 2.8 nm. A thickness-dependent spin reorientation transition from out-of-plane to in-plane anisotropy is identified as thickness increases, which is corroborated by the anomalous Hall effect measurements. This comprehensive study is essential for understanding the fundamental aspects of spin transport and offers valuable insights for optimizing magnetic tunnel junctions which are the key component of spintronic devices.