M.V. Rautskii

The optically induced and bias-voltage-driven magnetoresistive effect in a silicon-based device

The giant change in photoconductivity of a device based on the Fe/SiO2/p-Si structure in magnetic field is reported. As the magnetic field increases to 1 T, the conductivity changes by a factor of more than 25. The optically induced magnetoresistance effect is strongly dependent of the applied magnetic field polarity, as well as of sign and value of a bias voltage across the device. The main mechanism of the magnetic field effect is related to the Lorentz force, which deflects the trajectories of photogenerated carriers, thereby changing their recombination rate. The structural asymmetry of the device leads to the asymmetry of the dependence of recombination on the magnetic field polarity: recombination of carriers deflected in the bulk of semiconductor is relatively slow, while recombination of carriers at the SiO2/p-Si interface is faster. In the latter case, the interface states serve as effective recombination centers. The bias voltage sign specifies the type of carriers, whose trajectories pass near the interface, providing the main contribution to the magnetoresistance effect. The bias voltage controls the electric field accelerating carriers and, thus, affects the hole and electron trajectories. Moreover, when the bias voltage exceeds a certain threshold value, the electron impact ionization regime is implemented. The magnetic field suppresses impact ionization by enhancing recombination, which makes the largest contribution to the magnetoresistance of the device. The investigated device can be used as a prototype of silicon chips controlled simultaneously by optical radiation, magnetic field, and bias voltage.

Magnetoresonance properties of three-layer Co/Ge/Co films

Three-layer Co/Ge/Co films have been studied using electron magnetic resonance. It has been established that the resonance spectrum of the film is a superposition of two Lorentzian lines. It has been found that the anisotropy induced at the cobalt‒germanium interface makes the main contribution to the resonance spectrum and determines its features. The temperature dependences of the anisotropy field and the parameters of the interlayer exchange have been measured. The interlayer interactions exhibit an antiferromagnetic character and have been explained in terms of a model similar to the description of superexchange in magnetic dielectrics.

Room Temperature Spin Accumulation Effect in Boron Doped Si Created by Epitaxial Fe3Si/p-Si Schottky Contact

To study spin-dependent transport phenomena in Fe3Si/p-Si structures we fabricated 3-terminal planar microdevices and metal/semiconductor diode using conventional photolithography and wet chemical etching. I‒V curve of prepared diode demonstrates rectifying behavior, which indicates the presence of Schottky barrier in Fe3Si/p-Si interface. Calculated Schottky barrier height is 0.57 eV, which can provide necessary conditions for spin accumulation in p-Si. Indeed, in 3-terminal planar device with Fe3Si/p-Si Schottky contact Hanle effect was observed. By the analysis of Hanle curves spin lifetime spin diffusion length in p-Si were calculated, which are 145 ps and 405 nm, respectively (at T = 300 K). Spin lifetime strongly depends on temperature which can be related to the fact that spin-dependent transport in our device is realized via the surface states. This gives a perspective of creation of spintronic devices based on metal/semiconductor structure without need for forming tunnel or Schottky tunnel contact.

Magnetization Dynamics and Electron Transport in the La0.7Sr0.3MnO3/Y3Fe5O12 Hybrid Structures

We present the results of investigations of the spin-polarized current and spin dynamics in the hybrid structures ferrimagnetic insulator/ferromagnetic metal subjected to microwave radiation. We studied the La0.7Sr0.3MnO3/Y3Fe5O12 bilayer films on the Gd3Ga5O12 substrate. It was experimentally established that under the action of spin pumping the resistance of the La0.7Sr0.3MnO3 film changes. The value of ΔR is maximum in the sample with a La0.7Sr0.3MnO3 layer thickness of 10 nm and sharply drops as the manganite film thickness is increased. The resistance decreases in the paramagnetic region and grows in the ferromagnetic region at temperatures below the metal-insulator transition point. The variation in the resistance of the manganite film can be attributed to the correlation of the spin dynamics and transport properties of conduction electrons in the structure.

Interlayer Coupling in Co/Ge/Co Trilayers

The interlayer coupling in Co/Ge/Co trilayer films has been experimentally studied by the SQUID magnetometry and electron magnetic resonance. It has been found that the interlayer coupling is temperature-dependent. The values of the exchange constants have been determined.