Anisotropic Magnetoresistance Effect in Bulk Single-Crystal Half-Metallic Heusler Alloys

Crystal orientation dependence of the anisotropic magnetoresistance (AMR) of bulk single-crystal of Co
2
MnGe and Co
2
FeSi Heusler alloys was investigated. Negative AMR was observed in all crystal orientations [100, 110], and [111] for Co
2
MnGe, which has been predicted to be a half-metallic ferromagnet. On the other hand, both positive and negative signs of AMR were observed for Co2FeSi. For the interpretation of these behaviors, theoretical prediction based on the s-d scattering taking into consideration not only the spin-orbit interaction and exchange magnetic field but also the crystal field is required.