UC Riverside

Spin-based electronics, or spintronics, seeks to utilize the electron degree of freedom in order to perform logic, computation, or information storage. Proximity based interactions between nearby systems (i.e. films, adsorbates, molecules) and candidate spintronic materials (i.e. GaAs, graphene) could lead to the realization of novel phenomena. Such effects, which rely on atomic orbital overlap, require highly controlled surfaces and interfaces which can be achieved using molecular beam epitaxy (MBE). Here, this dissertation examines the feasibility of integrating high quality single crystal ferromagnetic insulators with oxide interfaces, the semiconductor GaAs, and graphene. Graphene, a single atomic layer of sp² bonded carbon with conducting &pi orbitals that extend out of the plane, is highly surface sensitive and can be considered an ideal material for investigating novel spin-based proximity related behavior. In particular, the interactions of functional oxides or adsorbates with graphene could lead to induced exchange splitting, magnetism, and spin-orbit coupling.

High quality crystalline deposition of the ferromagnetic insulator EuO is investigated with the primary focus of realizing high quality abrupt interfaces between the functional oxide and the spintronic material of choice. In this dissertation, stiochiometric EuO films are investigated on a wide variety of substrates including the spintronic relavent materials GaAs, 2-D planes of TiO₂, and sp² bonded carbon. The integration of EuO on these materials is a key advance towards experimental observation of the exchange proximity effect.

The atomic scale control over deposition provided by MBE allows for the investigation of submonolayer adsorbates (adatoms) and their interactions with graphene. In order to understand the effect of the adsorbates on spin-based properties and phenomena, we have performed systematic in-situ deposition of adatoms onto graphene non-local spin valves. Atomic hydrogen induces magnetic moments in graphene that couple via exchange to the injected spin current. This coupling results in an exchange field which causes the spins to precess rapidly with an effectively enhanced electron g-factor. These results demonstrate the power of molecular beam epitaxy in realizing novel graphene properties and functionality through careful control over the key interfaces and proximity materials.