Nano-structural materials and their physical properties for nano-spintronics

Abstract

Spintronics has been attracted much attention in the fields of future information technology because electronic device industries by only electrons have evolved into new paradigm of electrons with spins. For increase of volume, it is necessary to scale down the devices, thus a discovery of the materials for spintronics combined with nanotechnology has been much interested. In this dissertation, we report two proper nano-structural materials for the future nano-spintronics, Ag2Te and Fe1-xCoxSi. We report unconventional magneto-transport properties of an individual Fe1-xCoxSi nanowire. Below the Curie temperature (TC), we have studied dependence of the resistivity on the angle between the directions of the magnetization and electrical current. Observed anisotropic magnetoresistance (MR) ratio is negative, indicating that the conduction electrons in a minority spin band of the Fe1-xCoxSi nanowire dominantly contribute to the transport. Unlike typical ferromagnets, positive MR is observed in the overall temperature range. MR curves are linear below TC, and show a quadratic form above TC, which can be explained by the change of density of states arising from the band structures of Fe1-xCoxSi nanowire shift under a magnetic field. The temperature dependence of the resistivity curve is well explained by the Kondo effect. The Kondo temperature of a Fe1-xCoxSi nanowire is lower than that of the bulk state due to suppression of Kondo effect. High single-crystallinity of Fe1-xCoxSi nanowires allowed us to observe and interpret quite subtle variation of prominent intrinsic transport properties. Recently, the possibility has been suggested that Ag2Te is a topological insulator with highly anisotropic Dirac cone. We synthesize single crystalline Ag2Te nanowires and nanoplates with triple layered structure. We observe Aharanov-Bohm (AB) oscillation attributed to the quantum interference due to phase coherence around the perimeter of Ag2Te nanowire via transport measuremen...