Local structure studies of CoFeMnX (X = Si and Ge) Heusler alloys using X-ray absorption spectroscopy

•EXAFS studies are performed on CoFeMnX (X = Si, Ge).•Half-metallic CoFeMnGe is found to exist in a well-ordered LiMgPdSn structure.•Large antisite disorder is observed for spin gapless semiconductor (SGS) CoFeMnSi.•CoFeMnSi shows a high spin polarization of 64%.•SGS materials are supposed to be robust against chemical disorder.

In this paper, we report the local structure studies in CoFeMnX (X = Si and Ge) Heusler alloys using extended X-ray absorption fine structure (EXAFS) measurements. CoFeMnGe (CFMG) is found to exist in a well-ordered LiMgPdSn structure, while a large amount of antisite disorder is observed for CoFeMnSi (CFMS). CFMG is half-metallic ferromagnetic in nature, while CFMS is a spin gapless semiconductor (SGS). The presence of well-ordered crystal structure is an essential requirement to obtain high spin polarization in half-metallic materials, while SGS materials are supposed to be robust against chemical disorder. The fact that CFMS shows a high spin polarization of 64% even when having a high degree of disorder confirms that the SGS materials are robust against structural disorder.

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