Bulletin of the Russian Academy of Sciences: Physics最新文献

We studied the magnetoelectric effects in synthetic multiferroic structures, which are of significant interest for spintronic applications. Using advanced micromagnetic simulation techniques, we investigated magnetoelectric effects in several key synthetic structures, including ferromagnetic–multiferroic (with a uniform magnetic state) film, ferromagnetic-multiferroic structure with a spin cycloid as the ground state, and exchange-coupled ferromagnetic film characterized by non-uniform magnetoelectric effects. Our results reveal the diverse micromagnetic states achievable within these systems and highlight their corresponding magnetoelectric properties. The influence of non-collinear magnetic phases, which occur in noncentrosymmetric multiferroic and ferromagnetic structures, on the magnetization reversal processes of exchange-coupled films has been explored. The findings underscore the versatility of micromagnetic simulations in studying complex multiferroic structures, providing valuable insights for the design of next-generation spintronic devices.

We report a numerical study of the weakly diluted 4-state Potts model on a triangular lattice using Monte Carlo method. We consider systems with linear dimensions L × L = N, L = 10–160. Phase transitions in the Potts model are investigated employing the fourth-order Binder cumulants method and the histogram data analysis. Second-order phase transitions which are close to weakly first-order transitions are shown to occur in the 4-state Potts model on a triangular lattice. The addition of a nonmagnetic disorder has a stabilizing role in the realization of second-order phase transitions.

We considered the possibility of detecting a combined two-frequency effect of an alternating magnetic field in a ferrite plate. The main attention is paid to the properties of excited elastic oscillations when changing the magnitude of the alternating field and the plate thickness. The character and features of the magnetic and elastic oscillations excitation under resonance conditions at a difference frequency in linear and nonlinear cases are considered. It is noted that detection at the difference frequency has a pronounced nonlinear character, since it occurs only at a sufficiently high excitation level. The efficiency of elastic oscillations excitation at the difference frequency under various parameters of material and conditions has been evaluated.

Ga-doped Mn–Al alloys with compositions of Mn_58.5Al_31.8Ga_9.7 and Mn_58.3Al₃₄Ga_7.7 were produced by arc melting and subsequently successfully transformed into the ferromagnetic L1.0 phase. The pathways of complete transformations differed for the two alloys. For the 7.7 at % Ga alloy, a single-step cooling process at an intermediate rate was sufficient to transform it into the L1.0 phase. In contrast, the 9.7 at % Ga alloy required an additional annealing step at 550°C for 2 h to complete the transformation to the desired L1.0 structure. In second case the L1.0 phase consists of two distinct ferromagnetic L1.0 components with Curie temperatures of T_c1 = 302°C and T_c2 = 362°C, which evolved from different initial ε and γ₂ phases that were stable at 1100°C. The transformation of the γ₂ → τ phase was studied using electron back-scatter diffraction (EBSD), revealing that the τ(γ₂) phase began transforming from the interface and inherited the orientation of the τ(ε) phase at the interface, while the chemical compositions of both phases remained almost constant.

We studied the magnetic properties of Ni_{3 – x}Co_xB₂O₆ solid solutions with the kotoite structure, where x = 0; 0.19; 0.6; 0.93; 2. The compounds Ni₃B₂O₆ and Co₃B₂O₆ are antiferromagnets, with their easy axis of magnetization coinciding with the crystallographic directions c and b, respectively. In the Ni_2.81Co_0.19B₂O₆ solid solution, two features are found on magnetization curves, while in other solid solutions there is only one feature. With the cobalt ion concentration x > 0.9, the magnetic moments are predominantly oriented along the b axis.

We described the synthesis method and presents the results of a study of the magnetic and magnetotransport properties of vertical hybrid structures Fe₃Si/Ge/Mn₅Ge₃/Si. The mechanisms responsible for the detected magnetoresistive effect and the possible contribution of the spin-valve effect, realized through spin injection/extraction into/from germanium, are discussed.

Quasi-static hysteresis loops of spherical and spheroidal magnetite nanoparticles with semi-axes ratio a/b = 1.5 and 2.0 with different types of combined magnetic anisotropy are calculated using numerical simulation. For particles of each type the critical diameters D_cr are determined so that above D_cr the magnetization curling becomes the easiest mode of particle magnetization reversal. The hysteresis loops are calculated both for single-domain nanoparticles in the diameter range D_cr < D ≤ D_c, and for vortex particles with diameters D > D_c, where D_c is the single-domain diameter. The results obtained are compared with the hysteresis loops of single-domain particles with uniform magnetization rotation. The remanent magnetization and coercive force of oriented and non-oriented dilute assemblies of magnetite nanoparticles with different aspect ratios are determined as the functions of the transverse particle diameter.

We consider the spin wave resonances (SWRs) magnetoelastic excitation and electric detection in a hybrid bulk acoustic wave resonator containing YIG/Pt bilayer. The influence of micrometer and submicrometer yttrium iron garnet (YIG) film thickness on the efficiency of SWR excitation accompanied by a spin pumping from YIG to Pt has been theoretically studied. The frequency and thickness dependencies of inverse spin Hall effect (ISHE) voltage and microwave reflection coefficient are analytically and numerically investigated and discussed. Due to the non-uniform effective magnetic field of elastic nature, the higher SWR modes (both even and odd) can be excited with an efficiency comparable to the efficiency of the fundamental mode at the ferromagnetic resonance frequency. If an integer number of acoustic half-waves fits into the YIG film thickness, forbidden zones arise in the SWR spectrum: at certain thickness values, only even or only odd SWR modes are excited.

We presented the research results by impedance spectroscopy of frequency-dependent temperature activation of the conductivity and dielectric constant of the single-crystal magnetoelectric bismuth ferrite BiFeO₃, a promising functional material for RAM devices. The activation energies of low-temperature (110–300 K) processes of motion of charge carriers of the multiferroic structure and the logarithmic dependence of the critical temperatures between these processes on the frequency are determined in AC regime. It has been established that in this temperature range there is a correlation of AC characteristics with low- to high-temperature activation of the parameters of the BiFeO₃ crystal lattice.

We presented a setup created on the RADEX neutron channel at the Institute for Nuclear Research of the Russian Academy of Sciences to study the properties of highly excited states of light nuclei. The first experiment was carried out on the setup to determine the cluster structure of highly excited states of the ⁶Li nucleus in the reaction ⁶Li(n, ³He n)³H at a neutron energy of 50 ± 5 MeV. Several variants of the data collection system have been tested. A preliminary spectrum of the excitation energies of the ⁶Li nucleus has been obtained.