Probing the electronic states of high-TMR off-stoichiometric Co${}_{2}$MnSi thin films by hard x-ray photoelectron spectroscopy

Probing the electronic states of high-TMR off-stoichiometric Co $_{2}$ MnSi thin films by hard x-ray photoelectron spectroscopy

Xeniya Kozina, Julie Karel, Siham Ouardi, Stanislav Chadov, Gerhard H. Fecher, Claudia Felser, Gregory Stryganyuk, Benjamin Balke, Takayuki Ishikawa, Tetsuya Uemura, Masafumi Yamamoto, Eiji Ikenaga, Shigenori Ueda, and Keisuke Kobayashi

Phys. Rev. B 89, 125116 – Published 17 March 2014

Abstract

The tunnel magnetoresistance ratio (TMR) of fully epitaxial magnetic tunnel junctions with an off-stoichiometric Co $_{2}$ MnSi Heusler alloy has been shown to exhibit a systematic dependence on Mn content, reaching 1135% at 4.2 K for Co $_{2}$ Mn $_{1.29}$ Si. In this paper, we explain the behavior of the observed TMR ratio using ab initio calculations and hard x-ray photoelectron spectroscopy (HAXPES). For the Mn-deficient samples, we show that the the drop of the TMR is caused by Co antisite atoms, which impose extra states into the minority-spin band gap. On the other hand, Mn-excess composition shows nearly half-metallic behavior. This result can be intuitively understood since both Co $_{2}$ MnSi and Mn $_{2}$ CoSi are theoretically predicted to be half-metallic ferromagnets.