Spin Transport Signals Research Articles

Electric-field-induced spin injection enhancement.

The spin diffusion process can be modified by the electric field in a semiconductor channel. The electric field generated by the bias current improves the spin injection efficiency as well as the spin diffusion length at a ferromagnet-semiconductor hybrid system. Spin-polarized electrons from the ferromagnetic electrode were electrically investigated in an inverted heterostructure with an In0.53Ga0.47As active layer. Using local and non-local spin valve geometries, the interfacial spin polarizations with and without an electric field are extracted from the magnitude of spin transport signals. The interfacial spin polarization is increased from 3.2% to 7.0% with a current of 1 mA at T = 20 K. When the electric field assists the spin injection at the junction, the interfacial spin polarization remains 7% at the temperature ranged from 20 K to 200 K. Temperature dependence of the injected polarization shows that the electric field can compensate the thermal smearing of injection efficiency even at higher temperature.

Effect of contact geometry on spin-transport signals in nonlocal (Ga,Mn)As/GaAs devices

We report on spin-valve experiments in lateral spin-injection devices with different geometries of (Ga,Mn)As/GaAs spin Esaki diode contacts. We study the influence of the geometry of the contacts, i.e., their widths and the crystallographic orientation, on the magnetization reversal process and the resulting pattern observed in the spin-valve signal. We find that tuning of the magnetic anisotropy of the narrow (Ga,Mn)As stripes by means of lithographically induced anisotropic strain relaxation allows one to realize parallel, antiparallel, and even orthogonal configurations of magnetizations in injector and detector contacts. Understanding of the switching between these configurations during sweeping of the external in-plane magnetic field is crucial for a proper interpretation of the measured nonlocal spin signals.

Analysis and Design of Hanle-Effect Spin Transistors at 300 K

We propose a new Hanle-effect device based on a MOSFET type of spin transistor to reveal the dynamics of spin-polarized electron transport in the Si MOS inversion channel. The proposed device has the ability to detect spin signals with high sensitivity and to distinguish spin transport signals from other, spurious signals. Spin transport behavior induced by the Hanle effect in the device were theoretically analyzed and were well correlated with the universality of electron mobility in the MOS inversion channel. The Hanle-effect spin device can elucidate the true nature of spin transport in Si MOS inversion channels.

Gate Field Effect on Spin Transport Signals in a Lateral Spin-ValveDevice

Gate Field Effect on Spin Transport Signals in a Lateral Spin-ValveDevice

Interface resistance dependence of spin transport in a ferromagnet–semiconductor hybrid structure

The spin transport signals from NiFe and Co into two-dimensional electron gas layers are measured for various thicknesses of transmission barriers. A stable and reproducible electrical detection of spin transport was obtained only when the barrier thickness is less than 10 nm. The typical interface resistance to observe spin signals in this experiment is about 0.5–250 Ω, which is a neither transparent nor a severe tunneling limit. The optimal interface resistance depends on the ferromagnetic materials, but severe tunneling barrier is not proper for fully electrical spin transport. Device size is also a critical factor to decide the proper range of interface resistance.

35% magnetocurrent with spin transport through Si

Efficient injection of spin-polarized electrons into the conduction band of silicon is limited by the formation of a silicide at the ferromagnetic metal (FM)/silicon interface. In the present work, this “magnetically dead” silicide (where strong spin scattering significantly reduces injected spin polarization) is eliminated by moving the FM in the spin injector from the tunnel junction base anode to the emitter cathode and away from the silicon surface. This results in over an order-of-magnitude increase in spin injection efficiency, from a previously reported magnetocurrent ratio of ≈2% to ≈35% and an estimated spin polarization in Si from ≈1% to at least ≈15%. The injector tunnel junction bias dependence of this spin transport signal is also measured, demonstrating the importance of low bias voltage to preserve high injected spin polarization.