Electronic structure and magnetic anisotropy transition in Mn3−xCoxGa Heusler films investigated with soft x-ray spectroscopy

Abstract

Employing soft x-ray magnetic circular dichroism (XMCD) and soft x-ray absorption spectroscopy (XAS), we have investigated electronic structures and spin configurations of Co-substituted ${\mathrm{Mn}}_{3}\mathrm{Ga}$ (${\mathrm{Mn}}_{3\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{Ga}$) Heusler films, which are promising spintronic materials exhibiting perpendicular magnetic anisotropy (PMA). Co $2p$ XAS and XMCD measurements, combined with the charge-transfer multiplet analysis, show that the substituted Co ions in ${\mathrm{Mn}}_{3\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{Ga}$ consist of mainly ferromagnetic metallic Co clusters and a small amount of divalent Co ions with disordered magnetic moments. Mn $2p$ XAS and XMCD measurements show that Mn ions at both the octahedral and tetrahedral sites in ${\mathrm{Mn}}_{3\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{Ga}$ are nearly divalent with weak covalent-bonding nature, reflecting non-Jahn-Teller ions, and that the magnetic moments of Mn ions are polarized along the ordered magnetic moments of the substituted Co ions. Angle-dependent Co $2p$ XMCD data of ${\mathrm{Mn}}_{3\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{Ga}$ agree with the weak magnetic anisotropy transition from PMA to in-plane magnetic anisotropy (IMA) with increasing $x$. Spin and orbital magnetic moments of Co ions are estimated by using the sum-rule analysis, which reveal negligible Co-content and polar-angle dependencies of the Co orbital to spin magnetic moment ratio. This work reveals that the PMA-to-IMA magnetic transition in ${\mathrm{Mn}}_{3\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{Ga}$ is determined mainly by ferromagnetic metallic Co clusters.