S. G. Ovchinnikov

Magnetic-field- and bias-sensitive conductivity of a hybrid Fe/SiO2/p-Si structure in planar geometry

Pronounced magnetic-field- and bias-sensitive features of the transport properties of a Fe/SiO2/p-Si hybrid structure in planar geometry at temperature variation are investigated. Comparative analysis of two Fe/SiO2/p-Si samples, one with a continuous Fe film and the other with two electrodes formed from a Fe layer and separated by a micron gap, shows that these features are due to the metal-insulator-semiconductor (MIS) transition with a Schottky barrier near the interface between SiO2 and p-Si. Resistance of such a MIS transition depends exponentially on temperature and bias. In the structure with a continuous ferromagnetic film, the competition between conductivities of the MIS transition and the Fe layer results in the effect of current channel switching between the Fe layer and a semiconductor substrate. Within certain limits, this process can be controlled by a bias current and a magnetic field. Positive magnetoresistance of the structures at high temperatures is determined, most likely, by disorder...

Structural and Magnetic Characteristics of Fe/Si Bilayer and Multilayer Films Obtained by Thermal Deposition in Ultrahigh Vacuum

The structural and magnetic characteristics of Fe/Si bilayer and multilayer films with nanometer-thick layers obtained by thermal deposition in ultrahigh vacuum have been studied by methods of small-angle X-ray scattering, electron spectroscopy, and magnetometry. It is established that the mechanisms involved in the formation of Fe/Si and Si/Fe interfaces are different.

Extremely large magnetoresistance induced by optical irradiation in the Fe/SiO2/p-Si hybrid structure with Schottky barrier

We report giant magnetoresistance (MR) effect that appears under the influence of optical radiation in common planar device built on Fe/SiO2/p-Si hybrid structure. Our device is made of two Schottky diodes connected to each other by the silicon substrate. Photo-induced MR is positive and the MR ratio reaches the values in excess of 104%. The main peculiarity of the MR behavior is its strong dependence on the magnitude and the sign of the bias current across the device and, most surprisingly, upon polarity of the magnetic field. To explain such unexpected behavior of the MR, one needs to take into account contribution of several physical mechanisms. The main contribution comes from the existence of localized interface states at the SiO2/p-Si interface, which provide the spots for the photo-current conduction by virtue of the sequential tunneling through them or thermal generation and optical excitation of mobile charges. External magnetic field changes the probability of these processes due to its effect o...

Magnetic properties and nonmagnetic phases formation in "Fe/Si… n films

The magnetization of Fe/Si multilayers, grown by thermal evaporation in an ultrahigh vacuum system, was investigated at high temperatures. Magnetization and its temperature dependence up to a high temperature of 800 K depend on individual Fe layer thickness dFe. This dependence is the result of the formation of an Fe–Si interface layer (nonmagnetic phase) during the synthetic procedure. The fraction of this Fe–Si nonmagnetic phase is estimated versus dFe. At temperatures higher than 400 K an irreversible decrease in the magnetization occurs. A quantitative analysis of this irreversible behavior is proposed in terms of an exponential diffusion-like kinetic equation for the reaction that produces the Fe–Si nonmagnetic phase. The coefficients of the rate equation are the activation energy Ea and the prefactor D0, which have been determined for different dFe.

Frequency-dependent magnetotransport phenomena in a hybrid Fe/SiO2/p-Si structure

We report the large magnetoimpedance effect in a hybrid Fe/SiO2/p-Si structure with the Schottky barrier. The pronounced effect of magnetic field on the real and imaginary parts of the impedance has been found at temperatures 25–100u2009K in two relatively narrow frequency ranges around 1 kHz and 100u2009MHz. The observed frequency-dependent magnetotransport effect is related to the presence of localized “magnetic” states near the SiO2/p-Si interface. In these states, two different recharging processes with different relaxation times are implemented. One process is capture-emission of carriers that involves the interface levels and the valence band; the other is the electron tunneling between the ferromagnetic electrode and the interface states through SiO2 potential barrier. In the first case, the applied magnetic field shifts energy levels of the surface states relative to the valence band, which changes recharging characteristic times. In the second case, the magnetic field governs the spin-dependent tunneling...

Size effects and magnetization of (Fe/Si) n multilayer film nanostructures

The temperature dependence of the magnetization of (Fe/Si)n multilayer films with nanometer layers is investigated. The films are prepared through thermal evaporation under ultrahigh vacuum onto Si(100) and Si(111) single-crystal substrates. It is revealed that the thickness of individual iron layers in (Fe/Si)n multilayer films affects the magnetization and its temperature dependence. The inference is made that this dependence is associated with the formation of a chemical interface at the Fe-Si boundaries. The characteristics of the chemical interface in the (Fe/Si)n films are estimated.

Effect of the ferromagnetic layer thickness on the interlayer interaction in Fe/Si/Fe trilayers

Three-layer magnetic film systems Fe/Si/Fe have been studied by the method of magnetic resonance. It is established that the ferromagnetic layer thickness affects the magnitude of the interlayer exchange interaction in this system. A mechanism explaining the observed effect is proposed.

Quick ellipsometric technique for determining the thicknesses and optical constant profiles of Fe/SiO2/Si(100) nanostructures during growth

An algorithm is developed to perform rapid control of the thickness and optical constants of a film structure during growth. This algorithm is tested on Fe/SiO2/Si(100) structures grown in an Angara molecular-beam epitaxy setup. The film thicknesses determined during their growth are compared with X-ray spectral fluorescence analysis and transmission electron microscopy data.

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.

In situ investigations of magneto-optical properties of thin Fe layers

A thin polycrystalline Fe film on a single-crystal Si substrate with natural SiO2 oxide is obtained by thermal evaporation in ultrahigh vacuum. The magneto-optical properties of the resultant structure are investigated in situ by the methods of spectral ellipsometry. The values of the coercive force for the Fe film are obtained, and the magnetization reversal loop and the energy dependence of the equatorial Kerr effect are constructed. The effectiveness of magnetoellipsometry for in situ analysis of the geometrical and magnetooptical properties of thin ferromagnetic layers is demonstrated.