Voltage-controlled Spin Research Articles

ELECTRON-SPIN POLARIZATION IN BOTH MAGNETICALLY AND ELECTRICALLY-MODULATED NANOSTRUCTURES

We theoretically investigate the spin-dependent transport properties of electrons in realistic magnetic-electric barrier nanostructures, which are produced by the deposition, on top of a heterostructure, of a metallic ferromagnetic stripe with an applied voltage. The degree of the electron-spin polarization is found to be closely associated with this voltage, although the use of applied voltage itself induces no spin polarization effect. As a positive voltage is applied to the stripe the electron-spin polarization shifts towards the low-energy region and increases; it shifts towards the high-energy direction and reduces for a negative applied voltage. These results shown in this work imply that the degree of electron-spin polarization can be tuned by means of an applied voltage on the stripes of system, which may result in a practical voltage-controlled spin filter.

Selective Voltage-Controlled Hole Spin in Non-Magnetic Resonant Tunneling Diodes

We report theoretical and experimental observation of photoexcitated hole spin selection in GaAs/GaAlAs n-i-n in resonant tunneling diodes. When subjected to magnetic and electric parallel fields, the spin splitted hole levels leads to several peak structure in the transmissivity. These experimental results are interpreted as an evidence of tunneling transport through spin polarized hole levels of non-magnetic diodes.

Voltage-controlled spin selection in a magnetic resonant tunneling diode.

We have fabricated all II-VI semiconductor resonant tunneling diodes based on the (Zn,Mn,Be)Se material system, containing dilute magnetic material in the quantum well, and studied their current-voltage characteristics. When subjected to an external magnetic field the resulting spin splitting of the levels in the quantum well leads to a splitting of the transmission resonance into two separate peaks. This is interpreted as evidence of tunneling transport through spin polarized levels, and could be the first step towards a voltage controlled spin filter.

Quantum-well effect in magnetic tunnel junctions with ultrathin single-crystal Fe(100) electrodes

We studied the tunnel spectra of magnetic tunnel junctions with a single-crystal ultrathin Fe(100) electrode. The tunnel spectra show oscillations of the differential conductivity and the differential tunnel magnetoresistance. The positions of the maxima of the oscillations move systematically with the change in the Fe(100) electrode’s thickness, indicating that the oscillations originate from the quantum-well states in the ultrathin Fe(100) electrode. This effect provides us with an opportunity to create voltage-controlled spin functional devices.

Paramagnetic ion-doped nanocrystal as a voltage-controlled spin filter.

A theory of spin injection from a ferromagnetic source into a semiconductor through a paramagnetic ion-doped nanocrystal is developed. Spin-polarized current from the source polarizes the ion; the polarized ion, in turn, controls the spin polarization of the current flowing through the nanocrystal. Depending on voltage, the ion can either enhance the injection coefficient by several times or suppress it. Large ion spins produce stronger enhancement of spin injection.