Temperature ($T$)- and depth-dependent valence band (VB) electronic structures of an $\mathrm{Al}{\mathrm{O}}_x$-capped $L{2}_1$-ordered $\mathrm{C}{\mathrm{o}}_2\mathrm{MnSi}$ (CMS) thin film were studied by hard x-ray photoelectron spectroscopy (HAXPES) combined with x-ray total reflection (TR) to reveal the electronic states of the inside of CMS film (bulk) and near-interface region of CMS beneath the $\mathrm{Al}{\mathrm{O}}_x$ layer. The depth-dependent magnetic states of Co and Mn in CMS were also studied by magnetic circular dichroism (MCD) in core-level HAXPES measurements combined with TR. The VB HAXPES spectra obtained at $T=20$, 100, 200, and 300 K showed the clear $T$ dependence in the spectral shapes for both the near-interface and bulk regions of CMS, but the $T$ dependence of electronic states between the near-interface and bulk regions were different as well as the $T$-dependent magnetization of CMS for the near-interface and bulk regions obtained by the Co and Mn $2p$ core-level MCD-HAXPES measurements. The $T$-dependent VB HAXPES spectra of CMS in the bulk region qualitatively agreed with the electronic structure calculations with the disordered local moment method for bulk CMS, indicating the importance of the spin fluctuations on the electronic states of bulk CMS at a finite $T$ and the enhanced spin fluctuations in the near-interface region of CMS. These results suggest that the direct probing of the electronic and magnetic states of the insulator/ferromagnet heterojunctions in a nondestructive way is important to reveal the properties of ferromagnet for the near-interface and bulk regions at a finite $T$.

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• Electronic structure
• Spintronics
• Surface & interfacial phenomena
• Heusler alloy
• Photoemission spectroscopy