Spin Transport and Relaxation in Graphene and Germanium

In this thesis, I summarize our studies investigating the spin dependent properties of graphene over the last five years and the spin transport in germanium in the last three years. In the field of graphene spintronics, this thesis includes three major advances in these fields. First, room temperature spin transport in single layer graphene (SLG) is achieved using transparent contacts (Co/SLG) and an electron-hole asymmetry of spin transport in SLG is observed. Second, tunneling spin injection into SLG is achieved using TiO2 seeded MgO barriers. A large non-local magnetoresistance (MR) of 130 ohms is observed at room temperature. Third, long spin lifetime in SLG and bilayer graphene (BLG) are observed. Furthermore, strongly contrasting behavior for SLG and BLG is observed, in which SLG is dominant by Elliot-Yafet (EY) spin relaxation at low temperatures while In BLG is dominant by Dyakonov-Perel spin relaxation at low temperatures. In the field of spin transport in germanium (Ge), this thesis includes growth of single-crystalline, atomically smooth MgO film on Ge(001) by molecular beam epitaxy, the origin of Fermi level pinning in Ge Schottky junctions using epitaxially grown ultrathin MgO films, and electrical spin injection and transport in germanium using both nonlocal and three terminal spin transport methods