JETP Letters最新文献

The radiative heat exchange between two thick homogeneous isotropic plates undergoing relative nonrelativistic lateral motion is studied. Particular attention is paid to the symmetry properties of a system with the same or different parameters. It is shown that one of the gold plates (moving or stationary) in the quasi-stationary regime can be much more overheated than the other. These features can be used to experimentally study the Casimir–Lifshitz forces.

The magnetic properties of Mn_1–xRh_xSi solid solutions with a noncentrosymmetric structure B20 synthesized at a pressure of 8 GPa and temperatures of 1500–1770 K have been studied in detail in a wide temperature range of 2–300 K in magnetic fields up to 9 T. An anomalous increase in the Curie temperature T_C of compounds with 0.15 ≤ x ≤ 0.8 by a factor of 8.4–11.5 compared to the pure helical magnet MnSi has been found. It has been established that the Curie temperature T_C increases with the rhodium content to T_C(x = 0.15) = (244 ± 4) K, T_C(x = 0.4) = (299 ± 5) K, and T_C(x = 0.8) = (334 ± 6) K. Uniquely high magnetic transition temperatures up to room values occur in the disordered ferromagnetic Griffiths phase and may be due to the spin-fluctuation mechanism of enhancement of the magnetic interaction.

The effect of the finite mass of magnetic monopoles on the time and spatial dispersion of the magnetic susceptibility of spin ice is investigated. It is shown that the frequency dependence of the susceptibility in the low-frequency range follows the Debye law, while the susceptibility in the high-frequency range decreases more rapidly with an increase in the frequency. As a result, the sum rule violation typical of the Debye law is removed. The possibility of collective excitations, which are analogous to plasmons in systems with an electric charge, in a magnetic monopole system at high frequencies is also considered.

Spectroscopy experiments of the inelastic scattering of laser pulses in an aqueous suspension of silicon dioxide (SiO₂) nanoparticles at room temperature have revealed for the first time that the centroid of the OH Raman scattering band is shifted to the pump line up to 10 cm^–1 and two components of stimulated backward and forward Brillouin scattering with frequency shifts of ~7.5 and ~14.3 GHz are simultaneously generated. The frequency shift 7.5 GHz corresponds to the Stokes component of Brillouin scattering in water (speed of sound of ~1490 m/s), while the 14.3 GHz shift component corresponds to the speed of sound of ~2900 m/s; i.e., this component falls within the range of speeds of sound in ice at room temperature. In our opinion, the results of these experiments indicate both the formation of hydrate layers with an ice-like hydrogen bonding structure around SiO₂ nanoparticles and a decrease in the volumetric thermal expansion coefficient of the aqueous suspension.

A perforated plane ferromagnetic film with the inhomogeneous magnetoelectric interaction is theoretically studied. It is shown that an applied electric field can change the topology of the magnetic structure in such a film. Moreover, it is demonstrated that the distribution of the electric potential ensuring the occurrence of an arbitrary predetermined topology of the magnetic structure can be found. Explicit expressions determining the topology of the magnetic structure at the potential distribution are presented for the general and some particular cases.

Hysteresis loops in epitaxial rare-earth iron garnet (111) films at room temperature have been recorded using the magneto-optical Faraday effect. The magnetic field is applied in the film plane having the easy-plane magnetic anisotropy in combination with the cubic anisotropy, which allows out-of-plane magnetization. Suppression of the normal component of the magnetization due to with the effect of the magnetic anisotropy induced by 635-nm optical pump has been experimentally detected. It has been found that the effect depends on the direction of the wave vector of pump light in the crystal. This effect has been analyzed within the mechanism of the photoinduced excitation of hole polarons.

A number of new features in the magnetic, magnetoelectric, and magnetodielectric properties of the GdFeO₃ orthoferrite at phase transitions induced by a magnetic field H || a, b, c at low temperatures have been detected. A threefold increase in the permittivity in the form of peaks during spin-flip transitions in the Gd subsystem, which is accompanied by the suppression of the spontaneous electric polarization, as well as dielectric anomalies at a spin-reorientation (spin-flop) transition induced by the magnetic field H || a in the Gd and Fe subsystems in both ferroelectric ((T < T_{{text{N}}}^{{{text{Gd}}}})) and paraelectric ((T > T_{{text{N}}}^{{{text{Gd}}}})) phases, has been established. In the magnetic field H || c, below the magnetization compensation point, it has been found that an unusual transition occurs due to the reversal of the spontaneous weak-ferromagnetic moment of Fe from the direction against the magnetic field to the direction along the field and is accompanied by a break in its antiferromagnetic coupling to the Gd magnetic moment induced by the magnetic field. A proposed theoretical model including the exchange interactions allowed by symmetry and the magnetoelectric coupling has made it possible for the first time to consistently describe the temperature and field dependences of the permittivity and electric polarization.

Slow oscillations of the magnetoresistance periodic in the inverse magnetic field with a frequency of 3.4 T have been identified in HoTe₃. The temperature dependence of the oscillation amplitude is close to exponential even at low temperatures. This may be attributed to the existence of soft modes in the system and allows the estimation of the electron scattering rate on these modes. In the region of magnetic fields exceeding 1 T, the oscillations can be described as interference oscillations associated with the splitting of the band structure due to the bilayer structure of HoTe₃. The obtained data have allowed us to calculate the ratio ({{t}_{ bot }}{text{/}}{{t}_{z}} = 15.6) of the hopping integrals between layers (({{t}_{ bot }})) and within the bilayer (({{t}_{z}})) and to estimate these integrals as ({{t}_{ bot }}) ~ 2 meV and t_z ~ 0.26 meV.

The supercontinuum and third harmonic generation by focused infrared femtosecond laser pulses in distilled water in its normal and anomalous dispersion regions has been studied. Competition between the corresponding third-order nonlinearities has been detected: for pump wavelengths of 900–1200 nm (in the normal dispersion region), supercontinuum with the spectrum broadened predominantly to the blue region is generated. It has been found that 1300-nm femtosecond laser pulses propagating through the anomalous water dispersion region generate the third harmonic with the spectrum broadened to the red region. Saturation and reduction of the output of the third harmonic at a wavelength of 1300 nm with increasing pulse energy have been attributed to deterioration of phase matching as a result of ionization of the medium, which facilitates supercontinuum generation insensitive to phase matching.

A theory of the valley Hall effect in the hybrid system consisting of an electron gas and a Bose–Einstein condensate of dipole excitons formed on the basis of spatially separated monolayers of transition metal dichalcogenides has been proposed. The dependences of the transverse electric current on the spatial dimensions of the structure, as well as on the temperature and density of the electron gas, have been studied by analyzing the skew scattering of electrons on elementary excitations of the exciton Bose–Einstein condensate.