Experimental verification of the origin of positive linear magnetoresistance in CoFe ( V 1 − x Mn x ) Si Heusler alloys

The origin of the positive linear magnetoresistance (PLMR) effect at low temperatures in CoFe(V1−xMnx)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 L21B type. By employing the substitution of Mn for V in the CoFeVSi film in MBE conditions, we experimentally demonstrate homogeneous CoFe(V1−xMnx)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 CoFe(V0.5Mn0.5)Si. We note that the PLMR effect disappears for CoFe(V0.25Mn0.75)Si. According to theoretical calculations of the electronic band structures of CoFe(V1−xMnx)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 CoFe(V1−xMnx)Si can be experimentally controlled by substituting Mn for V. From these considerations, we can conclude that the PLMR effect in CoFe(V1−xMnx)Si is caused by the presence of the V state-induced gaplesslike structure in the minority spin electronic band near the Fermi level.