R. B. Morgunov

Magnetoresonant hardening of silicon single crystals

A microwave magnetic field crossed with a static field was found to exert a resonance effect on the dislocation mobility in single crystals of p-type silicon. The frequency of alternating field and the magnitude of static magnetic field corresponding to the maximal crystal hardening satisfy conditions for EPR of structural defects. This is evidence that the primary elementary processes observed previously in magnetoplasticity effects (influence of a static magnetic field on plasticity) are spin-dependent in silicon crystals. The dislocation path detected EPR spectrum was found to be anisotropic.

Magnetoplasticity and magnetic memory in diamagnetic solids

A mechanism for the depinning of dislocations pinned by a stopper is formulated. This mechanism includes the transfer of an electron from a dislocation to the stopper and the appearance of a spin two-electron nanoreactor that has no Coulomb interaction that would hold the dislocation at the stopper in the initial state. The spin dynamics in the nanoreactor is controlled by a magnetic field; therefore, it causes magnetoplasticity and short-term magnetic memory. Another origin of magnetoplasticity is the aggregation of diffusing paramagnetic ions (stoppers) into dimers, trimers, and clusters; this aggregation is also spin-selective and magnetically sensitive. The magnetic-field dependence of the structural evolution of the stoppers provides long-term magnetic memory in diamagnetic solids. Both mechanisms of magnetoplasticity and magnetic memory can coexist and be independent of or dependent on each other.

Spin dynamics in magnetic semiconductor nanostructures

The studies of the magnetic and electrical transport properties of ordered magnetic semiconductor nanostructures have been generalized. This new area lies at the intersection of nanotechnologies and fundamental problems of magnetism. The prospects for application of ferromagnetic semiconductors in spintronics have been discussed. A comparative analysis of the magnetic and electrical transport properties of nanowires, thin films, and bulk elemental semiconductors doped with transition metals has been performed. The influence of size effects on the spin dynamics, magnetization, and magnetoresistance of nanostructures has been considered.

Thermally-induced paramagnetism of spiropyrane iodides

Thermally stimulated paramagnetism has been found in the iodides of organic spiropyrane molecules, namely 1-isopropyl-3,3,5′,6′-tetramethylspiro(indolino-2,2′-[2H]pyrano[3,2-b]pyridinium) (SpSpSp) and spiro(1,3,3,7′-tetramethyl-indolino-2,3′-3H-pyrano[3,2-f]quinolinium) (Sp2Sp2). The activation energy of their triplet states was determined from the temperature dependence of their magnetic moments: 0.023 and 0.032 eV, respectively. It was found that the magnetic moment, μeff, increases under UV light (250–400 nm) due to the formation of high-spin (S = 3) states of the molecules.

Bifurcation of magnetic anisotropy caused by small addition of Sm in (Nd1−xSmxDy)(FeCo)B magnetic alloy

In sintered (Nd1−xSmxDy)(FeCo)B magnets, the contributions of “soft” (Nd1−xSmxDy)2(FeCo)2B and “hard” (Nd1−xSmxDy)2(FeCo)14B phases to the temperature and field dependences of magnetization have been distinguished. The increase in Sm concentration up to 3% provides stronger interlattice RE-TM (RE—rare-earth metals, TM—transition metals) exchange interaction. Contributions of the NdDy and Sm to magnetic anisotropy have been determined. The competition between the positive contribution of Nd and Dy and the negative contribution of Sm ions results in non-monotonous temperature and Sm concentration dependencies of anisotropy field. Anisotropy of the studied alloys is intermediate between “easy axis” and “easy plane” symmetry.

Magnetic field effect on spin dependent conversion of nonequilibrium Si-O chemical bonds on the Czochralski-grown Si crystal surface

The magnetic field effect on the surface oxidation of Czochralski-grown Si single crystals has been observed via atomic force microscopy, electron microscopy, secondary emission ion and Auger spectroscopy, and x-ray photoelectron spectroscopy. The changes in the concentration of oxygen complexes and chemical elements on the crystal surface exposed to a magnetic field of 0.17 T are evidence of spin dependent surface reactions involving unstable intermediate Si–O–Si complexes as precursors. The experimental data have been discussed in terms of the theory of spin dependent reactions controlled by magnetic field.

Electron spin resonance in InGaAs/GaAs heterostructures with a manganese δ layer

The static and high-frequency dynamic magnetic properties and photoluminescence of two-dimensional semiconductor GaAs heterostructures containing an InGaAs quantum well and a thin manganese layer (δ layer) are studied. It is found that the Curie temperature is TC ≈ 35 K and the magnetic anisotropy field of the ferromagnetic manganese δ layer is Ha ≈ 600 Oe. The spin resonance spectrum exhibits a line in weak fields (from −50 to 100 Oe), which is observed in the same temperature interval T < 40 K where the ferromagnetic ordering of the manganese δ layer occurs. This line is probably caused by the nonresonance contribution of the spin-dependent scattering of charge carriers to the negative magnetic resistance. The dependence of the degree of polarization of photoluminescence on the magnetic field also points to the ferromagnetic behavior of the manganese δ layer.

Effect of a weak magnetic field on the state of structural defects and the plasticity of ionic crystals

The aim of this work is to examine the influence of a weak (on the energy scale) magnetic field on the state of dislocations and point defects in ionic crystals. It is found that complex point defects existing in a metastable state are sensitive to a magnetic field B∼1 T. The contributions are identified, and the kinetics of various types of reactions within the structural defects and between them leading to plastification of the crystals in a magnetic field are determined. The effect of light on the sensitivity of the point defects to a magnetic field is described, and the spectral characteristics of this effect are determined. A resonant effect of the combined action of a weak constant magnetic field and a high-frequency magnetic field on the dislocation mobility is found to occur when these fields satisfy the conditions of electron paramagnetic resonance.

Magnetic phase transition in ɛ-InxFe2 − xO3 nanowires

This paper reports on a study of magnetic properties of ordered arrays of ɛ-InxFe2 − xO3 (x = 0.24) nanowires possessing a high room-temperature coercive force of 6 kOe. Lowering the temperature below 190 K brings about a sharp decrease of the coercive force and magnetization of nanowires driven by the magnetic phase transition from the ferrimagnetic into antiferromagnetic phase. The transition is accompanied by a decrease of the magnetic anisotropy constant, which accounts for the anomalous frequency dependence of the position of the maximum in the temperature dependence of dynamic magnetic susceptibility. In the low-temperature phase, a spin-flop transition in the magnetic field of 28 kOe has been observed at T = 2 K. Lines related to the high-temperature hard-magnetic and low-temperature phases have been identified in electron spin resonance spectra of the nanowires. A line lying near zero magnetic field and evolving from the nonresonant signal related to the microwave magnetoresistance of the sample has also been detected.

Ferromagnetism and microwave magnetoresistance of GaMnSb films

The influence of the concentration of holes on the ferromagnetism of MnSb clusters in GaMnSb films has been revealed. It has been found that the high concentration of holes leads to their tunneling through the Schottky barrier at the cluster-crystal lattice interface and to a change in the magnetization of clusters. The microwave resistance of the films depends on the spin polarization of holes, which is controlled by the magnetization of clusters and the external magnetic field. The parameters of the crystalline anisotropy of ferromagnetic clusters and the dipole-dipole interaction between them have been determined.