Magnetotransport properties and kondo effect observed in a ferromagnetic single-crystalline Fe(1-x)Co(x)Si nanowire.

We report unconventional magnetotransport properties of an individual Fe(1-x)Co(x)Si 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-x)Co(x)Si 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-x)Co(x)Si 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-x)Co(x)Si nanowire is lower than that of the bulk state due to suppression of the Kondo effect. The high single crystallinity of Fe(1-x)Co(x)Si nanowires allowed us to observe and interpret quite subtle variations in the prominent intrinsic transport properties.