Experimental verification of the origin of positive linear magnetoresistance in CoFe(V1−xMnx)Si Heusler alloys

Abstract

The origin of the positive linear magnetoresistance (PLMR) effect at low temperatures in $\mathrm{CoFe}({\mathrm{V}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x})\mathrm{Si}$ Heusler alloys is discussed. From anomalous dispersion x-ray diffraction measurements, we can clarify that the crystal structure of the epitaxial CoFeVSi films grown by molecular beam epitaxy (MBE) is $L{2}_{1}\mathrm{B}$ type. By employing the substitution of Mn for V in the CoFeVSi film in MBE conditions, we experimentally demonstrate homogeneous $\mathrm{CoFe}({\mathrm{V}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x})\mathrm{Si}$ films and systematic control of the magnetic moments. The PLMR effect gradually decreases with increasing Mn contents but it can be seen even for $\mathrm{CoFe}({\mathrm{V}}_{0.5}{\mathrm{Mn}}_{0.5})\mathrm{Si}$. We note that the PLMR effect disappears for $\mathrm{CoFe}({\mathrm{V}}_{0.25}{\mathrm{Mn}}_{0.75})\mathrm{Si}$. According to theoretical calculations of the electronic band structures of $\mathrm{CoFe}({\mathrm{V}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x})\mathrm{Si}$, the gaplesslike electronic band structure due to the V-$d$ state in the minority spins of CoFeVSi is varied to the band gap by increasing the substitution of Mn. This means that the electronic band structure near the Fermi level in $\mathrm{CoFe}({\mathrm{V}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x})\mathrm{Si}$ can be experimentally controlled by substituting Mn for V. From these considerations, we can conclude that the PLMR effect in $\mathrm{CoFe}({\mathrm{V}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x})\mathrm{Si}$ is caused by the presence of the V state-induced gaplesslike structure in the minority spin electronic band near the Fermi level.