D. A. Maslov

Temperature-dependent magnetospectroscopy of HgTe quantum wells

We report on magnetospectroscopy of HgTe quantum wells in magnetic fields up to 45 T in temperature range from 4.2 K up to 185 K. We observe intra- and inter-band transitions from zero-mode Landau levels, which split from the bottom conduction and upper valence subbands, and merge under the applied magnetic field. To describe experimental results, realistic temperature-dependent calculations of Landau levels have been performed. We show that although our samples are topological insulators at low temperatures only, the signature of such phase persists in optical transitions at high temperatures and high magnetic fields. Our results demonstrate that temperature-dependent magnetospectroscopy is a powerful tool to discriminate trivial and topological insulator phases in HgTe quantum wells.

Dynamics of Magnetization in Frustrated Spin-Chain Systems: Ca3Co2O6

A two-dimensional Ising-like model for the triangular spin-chain lattice, where each spin chain is treated as a rigid superspin, is proposed to investigate the dynamics of magnetization in frustrated triangular spin-chain systems. The superspins are assumed to interact with the nearest neighbours and external agency (heat reservoir and external magnetic field) that causes them to change their states randomly with time. A probability of a single spin-flip process is assumed in a Glauber-like form. This technique allows describing the steps in the magnetization curves observed in Ca3Co2O6 and their dependence on the magnetic field sweep rate and temperature.

Investigation of magnetoabsorption at different temperatures in HgTe/CdHgTe quantum-well heterostructures in pulsed magnetic fields

The magnetoabsorption in magnetic fields as high as 40 T is investigated at T > 77 K in HgTe/CdHgTe quantum-well heterostructures (dQW ≈ 8 nm). The spectra reveal two lines associated both with intraband transition from the lower Landau level in the conduction band and with interband transition. It is shown that the band structure in these systems changes from inverted to normal with increasing temperature.

High Magnetic Field Facility for Cyclotron Resonance Investigation in Semiconductors

In this paper, a compact high magnetic field facility for cyclotron resonance (CR) investigation in the mid-infrared range is presented. A technology of multiturn coils winding with microcomposite Cu-Nb wire was developed in the Sarov Physics and Technology Institute Norwegian University of Science and Technology Moscow Engineering Physics Institute for the fabrication of compact nondestructive solenoids up to 50 T. An optical scheme and details of experimental techniques of CR measurements are discussed. Two peaks of magnetic absorption at 28 THz were observed in a narrow-gap HgTe/Hg1-xCdxTe heterostructures with quantum wells at 80 K.

A compact research facility for pulsed high magnetic fields of up to 50 T

A facility for generating pulsed magnetic fields with a millisecond duration and maximum peak values of 50 T is presented. The solenoid is produced from a Cu–Nb microcomposite conductor and is reinforced with a bandage made from Armos para-aramid fiber. The capacitor bank is switched to the high magnetic field solenoid by means of a solid-state switch board based on a module of reversely connected dynistors. Since the diameter of the working hole is 19.5 mm, it is possible to place a cryostat in it with operating temperatures as low as the helium temperatures and to measure the magnetization, the complex conductance, and the optical characteristics of substances in the visible and IR ranges. The operation features of the facility are discussed.

The efficiency of backward magnetic-pulse processing

The dependence of the efficiency of magnetic-pulse processing of materials on the pulsed magnetic-field shape has been studied. It is shown that, by using a pulse train instead of a single pulse in the fast-rising component of a magnetic field applied during the backward forming process, it is possible to increase the specific mechanical impulse transferred to a workpiece and, thus, improve the efficiency of processing. Possible applications of the proposed method to removing dents from car chassis and aircraft parts are considered

Charge Ordering of Multiferroic LuFe2O4: Influence of Doping and Electric Field

Charge ordering of nonstoichiometric LuFe2O4+δ is discussed. Properties of triangular bilayer are investigated via mean field theory with Coulomb interaction between sites. It is shown that low temperature state of bilayer has dipole moment essentially under any doping parameter. Correlation between sites in neighbor layers is estimated and dimer partially disordered antiferroelectric phase is extended for the case of nonstoichiometric samples. Competition of correlation effect with bilayer interaction and external electric field is discussed. Phase diagrams for doped specimen are presented. The results of investigation are used to clarify a significant surface impact.

Charge ordering of LuFe 2 O 4 electronic multiferroic

Charge ordering of iron ions in LuFe2O4 frustrated electronic ferroelectric with variable valence is considered. Charge degrees of freedom are described in frameworks of Ising model with Coulomb interaction between sites. Mean field approximation is used to find free energies of the most probable structures. Phase diagrams of a single triangular bilayer and a system of triangular bilayers are plotted. A partially disordered dimer structure is proposed as a 2D high temperature phase. The transition from 2D to 3D ordering associated with a drop in temperature and the formation of spontaneous dipole moments is discussed.

Dynamics of magnetization of frustrated ising systems

The dynamics of magnetization in triangle lattices of the Ising chains has been investigated in terms of the Glauber theory. The results of three-dimensional numerical simulation of the magnetic structure and magnetization curves of Ca3Co2O6 are presented. The structures of the low-temperature and high-temperature phases differ significantly: the false frustrated low-temperature phase is transformed into a partially disordered antiferromagnetic honeycomb structure. Two additional magnetization steps at low temperatures are formed at the expense of the domain structure and the ferrimagnetic phase. All fundamental hypotheses used in terms of the two-dimensional model have found their confirmation during the three-dimensional simulation.

Magnetic Structure of Fe/V Superlattices with Variable Thickness of Iron Layers

The model of magnetic structure of Fe/V superlattices is discussed. An individual iron layer of 2 or 3 ML in thickness is assumed to be a XY system. An interlayer interaction through vanadium spacers leads to the appearing of effective field for each iron layer. The infinite and finite superlattices are investigated. Calculations of magnetic structure of Fe2/V12/Fe3/V12 superlattice show that divergence in estimations of the critical temperature obtained by neutron scattering and MOKE is due to inhomogeneity of magnetic moment distribution in the finite superlattice.