Roland Kawakami

Tunneling Spin Injection into Single Layer Graphene

We achieve tunneling spin injection from Co into single layer graphene (SLG) using TiO₂ seeded MgO barriers. A nonlocal magnetoresistance (ΔR(NL)) of 130  Ω is observed at room temperature, which is the largest value observed in any material. Investigating ΔR(NL) vs SLG conductivity from the transparent to the tunneling contact regimes demonstrates the contrasting behaviors predicted by the drift-diffusion theory of spin transport. Furthermore, tunnel barriers reduce the contact-induced spin relaxation and are therefore important for future investigations of spin relaxation in graphene.

Giant Planar Hall Effect in Epitaxial (Ga,Mn)As Devices

Large Hall resistance jumps are observed in microdevices patterned from epitaxial (Ga,Mn)As layers when subjected to a swept, in-plane magnetic field. This giant planar Hall effect is 4 orders of magnitude greater than previously observed in metallic ferromagnets. This enables extremely sensitive measurements of the angle-dependent magnetic properties of (Ga,Mn)As. The magnetic anisotropy fields deduced from these measurements are compared with theoretical predictions.

Spin Relaxation in Single-Layer and Bilayer Graphene

We investigate spin relaxation in graphene spin valves and observe strongly contrasting behavior for single-layer graphene (SLG) and bilayer graphene (BLG). In SLG, the spin lifetime (τ(s)) varies linearly with the momentum scattering time (τ(p)) as carrier concentration is varied, indicating the dominance of Elliot-Yafet (EY) spin relaxation at low temperatures. In BLG, τ(s) and τ(p) exhibit an inverse dependence, which indicates the dominance of Dyakonov-Perel spin relaxation at low temperatures. The different behavior is due to enhanced screening and/or reduced surface sensitivity of BLG, which greatly reduces the impurity-induced EY spin relaxation.

Electronic doping and scattering by transition metals on graphene

We investigate the effects of transition metals (TM) on the electronic doping and scattering in graphene using molecular-beam epitaxy combined with in situ transport measurements. The room-temperature deposition of TM onto graphene produces clusters that dope

2-Dimensional Transition Metal Dichalcogenides with Tunable Direct Band Gaps: MoS2(1–x)Se2x Monolayers

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Control of Schottky Barriers in Single Layer MoS2 Transistors with Ferromagnetic Contacts

type for all TM investigated (Ti, Fe, and Pt). We also find that the scattering by TM clusters exhibits different behavior compared to

(Ga,Mn)As as a digital ferromagnetic heterostructure

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Magnetic moment formation in graphene detected by scattering of pure spin currents.

Coulomb scattering. At high coverage, Pt films are able to produce doping that is either

Spin-polarized Zener tunneling in (Ga, Mn)As

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Investigating the origin of Fermi level pinning in Ge Schottky junctions using epitaxially grown ultrathin MgO films

type or weakly