Magnetotransport Properties and Kondo Effect Observed in a Ferromagnetic Single‐Crystalline Fe1−xCoxSi Nanowire

We report unconventional magnetotransport properties of an individual Fe_1?xCo_xSi nanowire. We have studied the dependence of the resistivity on the angle between the directions of the magnetization and electrical current below the Curie temperature (T_C). The observed anisotropic magnetoresistance (MR) ratio is negative, thereby indicating that the conduction electrons in a minority spin band of the Fe_1?xCo_xSi nanowire dominantly contribute to the transport. Unlike typical ferromagnets, positive MR is observed in the overall temperature range. MR curves are linear below T_C and show a quadratic form above T_C, which can be explained by the change of density of states that arises as the band structures of the Fe_1?xCo_xSi nanowire shift under a magnetic field. The temperature dependence of the resistivity curve is sufficiently explained by the Kondo effect. The Kondo temperature of the Fe_1?xCo_xSi nanowire is lower than that of the bulk state due to suppression of the Kondo effect. The high single crystallinity of Fe_1?xCo_xSi nanowires allowed us to observe and interpret quite subtle variations in the prominent intrinsic transport properties.