Sergei V. Demishev

Spin-polaron transport and magnetic phase diagram of iron monosilicide

The study of galvanomagnetic, magnetic, and magnetooptical characteristics of iron monosilicide in a wide range of temperatures (1.8–40 K) and magnetic fields (up to 120 kOe) has revealed the origin of the low-temperature sign reversal of the Hall coefficient in FeSi. It is shown that this effect is associated with an increase in the amplitude of the anomalous component of the Hall resistance ρH (the amplitude increases by more than five orders of magnitude with decreasing temperature in the range 1.8–20 K). The emergence of the anomalous contribution to ρH is attributed to the transition from the spin-polaron to coherent regime of electron density fluctuations in the vicinity of Fe centers and to the formation of nanosize ferromagnetic regions, i.e., ferrons (about 10 Å in diameter), in the FeSi matrix at T<TC=15 K. An additional contribution to the Hall effect, which is observed near the temperature of sign reversal of ρH and is manifested as the second harmonic in the angular dependences ρH(ϕ), cannot be explained in the framework of traditional phenomenological models. Analysis of magnetoresistance of FeSi in the spin-polaron and coherent spin fluctuation modes shows that the sign reversal of the ratio Δρ(H)/ρ accompanied by a transition from a positive (Δρ /ρ>0, T>Tm) to a negative (Δρ/ρ<0, T<Tm) magnetoresistance is observed in the immediate vicinity of the mictomagnetic phase boundary at Tm=7 K. The linear asymptotic form of the negative magnetoresistance Δρ/ρ ∝−H in weak magnetic fields up to 10 kOe is explained by the formation of magnetic nanoclusters from interacting ferrons in the mictomagnetic phase of FeSi at T<Tm. The results are used for constructing for the first time the low-temperature magnetic phase diagram of FeSi. The effects of exchange enhancement are estimated quantitatively and the effective parameters characterizing the electron subsystem in the paramagnetic (T>TC), ferromagnetic (Tm<T< TC), and mictomagnetic (T<Tm) phases are determined. Analysis of anomalies in the aggregate of transport, magnetic, and magnetooptical characteristics observed in the vicinity of Hm≈35 kOe at T<Tm leads to the conclusion that a new collinear magnetic phase with M∥H exists on the low-temperature phase diagram of iron monosilicide.

The bulk amorphous A3B5 semiconductor: Technological and physical aspects

Abstract Electrophysical properties of the bulk amorphous A 3 B 5 semiconductor a-GaSb are studied for the first time. It is shown that in amorphous-crystalline gallium antimonide system a metal-insulator transition can be induced as the content of the amorphous phase increases gradually. Analysis of the relaxation of electrical conductivity demonstrated the complex nature of amorphous phase in GaSb which can be subdivided into some units.

Anomalous polarization characteristics of magnetic resonance in a quasi-one-dimensional CuGeO3: Co magnet

Doping of CuGeO3 by 2% Co was found to cause a new magnetic resonance, which has anomalous polarization characteristics. In the Faraday geometry, where a microwave field Bω is directed along certain crystallographic directions, this mode is suppressed, which indicates that the character of magnetic oscillations in this mode differs strongly from standard spin precession. This resonance coexists with the EPR on Cu2+ chains and is likely to be caused by an unknown collective mode of magnetic oscillations of an antiferromagnetic quantum S = 1/2 spin chain.

Non-equilibrium crystallization of non-crystalline solids. The explosive crystallization modelling

Abstract Explosive crystallization has been modeled based on new mechanisms of local phase transitions in a volume defined by a medium-range order length, L MRO , and energy localization on the phase transition front. Within this model threshold characteristics, temperature on the front and the explosive crystallization rate, ν ex , are estimated. The phase transition wave structure is analyzed qualitatively. It is shown that the obtained results conform with known experimental data. It is found that a fundamental timescale defining explosive process kinetics is given by a relation L MRO / ν ex and is of the order of 10 −9 s. Analytical expressions for ν ex in the framework of different models of energy localization in phonon spectra are suggested.