Electronic and magnetic properties of off-stoichiometric Co$_\mathrm{2}$Mn$_{\beta}$Si/MgO interfaces studied by x-ray magnetic circular dichroism

TL;DR

This study investigates how off-stoichiometry in Co2MnβSi/MgO interfaces affects electronic and magnetic properties, revealing that Mn and Co magnetic moments decrease with increased Mn content, aligning with first-principles calculations and TMR ratio observations.

Contribution

The paper provides a detailed analysis of the Mn composition dependence of magnetic moments at CMS/MgO interfaces using XMCD and first-principles modeling, highlighting the role of antisite defects.

Findings

Mn and Co magnetic moments decrease with increasing Mn composition

Antisite defect concentration decreases with higher Mn content, improving half-metallicity

Higher TMR ratios observed for Mn-rich CMS electrodes

Abstract

We have studied the electronic and magnetic states of Co and Mn atoms at the interface of the Co$_\mathrm{2}$Mn$_{\beta}$Si (CMS)/MgO ($\beta$=0.69, 0.99, 1.15 and 1.29) magnetic tunnel junction (MTJ) by means of x-ray magnetic circular dichroism. In particular, the Mn composition ($\beta$) dependences of the Mn and Co magnetic moments were investigated. The experimental spin magnetic moments of Mn, $m_\mathrm{spin}$(Mn), derived from XMCD weakly decreased with increasing Mn composition $\beta$ in going from Mn-deficient to Mn-rich CMS films. This behavior was explained by first-principles calculations based on the antisite-based site-specific formula unit (SSFU) composition model, which assumes the formation of only antisite defect, not vacancies, to accommodate off-stoichiometry. Furthermore, the experimental spin magnetic moments of Co, $m_\mathrm{spin}$(Co), also weakly decreased with increasing Mn composition. This behavior was consistently explained by the antisite-based SSFU model, in particular, by the decrease in the concentration of Co$_\mathrm{Mn}$ antisites detrimental to the half-metallicity of CMS with increasing $\beta$. This finding is consistent with the higher TMR ratios which have been observed for CMS/MgO/CMS MTJs with Mn-rich CMS electrodes.