Jae Hyun Kwon

Control of Spin Precession in a Spin-Injected Field Effect Transistor

Transistors Switch onto Spin Using the spin of an electron in addition to, or instead of, the charge properties is believed to have many benefits in terms of speed, power-cost, and integration density over conventional electronic circuits. At the heart of the field of spintronics has been a proposed spin-analog of the electronic transistor, the spin field effect transistor. Koo et al. (p. 1515) demonstrate the injection and detection of spin between two ferromagnetic contacts and show how the magnitude of the spin-current between the source and drain contacts can be controlled by a voltage applied to a gate. The results present an experimental realization of the concepts described for the spin-transistor. A field-effect transistor in which the spin current is controlled by a gate voltage is demonstrated. Spintronics increases the functionality of information processing while seeking to overcome some of the limitations of conventional electronics. The spin-injected field effect transistor, a lateral semiconducting channel with two ferromagnetic electrodes, lies at the foundation of spintronics research. We demonstrated a spin-injected field effect transistor in a high-mobility InAs heterostructure with empirically calibrated electrical injection and detection of ballistic spin-polarized electrons. We observed and fit to theory an oscillatory channel conductance as a function of monotonically increasing gate voltage.

Channel width effect on the spin-orbit interaction parameter in a two-dimensional electron gas

The spin splitting energy obtained from the Shubnikov–de Haas oscillation increases with decreasing channel width (w) of the InAs-based heterostructure. Since the surface charge concentration depends only weakly on w, the channel width dependence of the spin splitting energy is attributed to variations in the spin-orbit interaction strength. The spin-orbit interaction parameter was found to be inversely proportional to w in the range of w=2–64μm. Our findings indicate that a strong spin-orbit interaction is induced in a narrow channel due to suppression of the spin precession length for a thin quantum well layer system.The spin splitting energy obtained from the Shubnikov–de Haas oscillation increases with decreasing channel width (w) of the InAs-based heterostructure. Since the surface charge concentration depends only weakly on w, the channel width dependence of the spin splitting energy is attributed to variations in the spin-orbit interaction strength. The spin-orbit interaction parameter was found to be inversely proportional to w in the range of w=2–64μm. Our findings indicate that a strong spin-orbit interaction is induced in a narrow channel due to suppression of the spin precession length for a thin quantum well layer system.

Gate modulation of spin precession in a semiconductor channel

Gate control of spin precession is experimentally presented in an InAs quantum well with ferromagnetic spin injector and detector. The gate electric field modulates the spin–orbit interaction and spin precession. As a consequence, spin dependent conductance in the InAs channel is controlled by the gate voltage. Using ballistic spin transport theory, gate modulation results are proved to fit very well with gate voltage dependence of Rashba field strength.

Electric Field Effect on Spin Diffusion in a Semiconductor Channel

In the diffusive regime, the accumulated spins diffuse out symmetrically in both directions of the InAs channel and the spin signal exponentially decays with the distance. However, considering spin drift induced by the applied electrical current, the spin diffusion occurs in an asymmetric manner. Nonlocal measurements of a lateral spin-valve structure show that the amount of spin polarized electron depends on the direction of the electric field. The magnitude of the nonlocal signal difference due to the bias-current-induced drift effect diminishes from 5.6 mOmega at T=20 K to close to zero at T=300 K.

Edge Shape Effect on Switching Behavior in a Small Ferromagnetic Pattern

Switching behavior and domain structure greatly depends on the edge shape of mesoscopic patterns. In our simulation, permalloy patterns with elliptical and tapered edge need 80% and 50% more switching field, respectively, than a rectangle for the same overall aspect ratio of four. In the switching dynamics, vortex nucleation and its initial location play a great role in deciding switching field. Elliptical and tapered patterns show high magnetic remanence, which is advantageous for non-volatile device application. It is also demonstrated that small control of tapered edge makes it possible to change the switching behavior without the variation of overall aspect ratio.