Solid State Phenomena Vols. 168-169

Abstract: The spectrum of standing exchange magnon wave in FeNi alloy films obtained by thermal evaporation method is studied. The modification of dispersion law conditioned by magnetization fluctuations is detected. The films of invar structure having metastable bcc structure are most dispersing relative to magnetic state. The size of magnetic inhomogeneity was less than 5 nm.

Abstract: The dynamic susceptibility and the one-dimensional density of states (DOS) of an initially sinusoidal superlattice (SL) with simultaneous presence of two-dimensional (2D) phase inhomogeneities that simulate the deformations of the interfaces between the SL’s layers and three-dimensional (3D) amplitude inhomogeneities of the layer material of the SL were investigated. An analytical expression for the averaged Green’s function of the sinusoidal SL with 2D phase inhomogeneities was obtained in the Bourret approximation. It was shown that the effect of increasing asymmetry of heights of the dynamic susceptibility peaks at the edge of the Brillouin zone of the SL, which was found in [6] at increasing the rms fluctuations of 2D inhomogeneities, also takes place at increasing the correlation wave number of such inhomogeneities. It was also shown that the increase of the rms fluctuations of 3D amplitude inhomogeneities in the superlattice with 2D phase inhomogeneities leads to the suppression of the asymmetry effect and to the decrease of the depth of the DOS gap.

Abstract: The interaction between two wave fields of different nature that are caused by rms fluctuations of the coupling parameter between these fields in media with zero-mean coupling parameter is considered. Taking into consideration the multiple scattering processes of waves on the inhomogeneities leads to the results considerably different from those that have been obtained for the same situation in the Bourret approximation earlier [4,5]. Instead of the degeneration removal of frequencies in the wave spectrum and the appearance of two resonance peaks in the dynamic susceptibility at the intersection of the initial dispersion laws, the sharp broadening of the self-mode peak has to be observed. The consideration is done by the example of magnetoelastic waves in zero-mean magnetostrictive media.

Abstract: We consider unstable motion in small magnetic particles, driven by an external magnetic field and influenced by thermal fluctuations. Our studies demonstrate both temporal and spatial complexity of the dynamics in this system. The results are obtained using numerical simulations of the Landau-Lifshitz-Gilbert equations.

Abstract: The spin-orbital subsystem model with electron clusters was used for studying the frequency spectra ferromagnetic resonance (FMR). A new type of ferromagnetic order and new region of FMR were found. The new region may be in the microwave region or in the infrared region (IR). The volume of spin-orbital electron cluster is equal to 1-50 cubic nanometer approximately.

Abstract: We propose a new mechanism of exciton-magnon absorption in the 1D Heisenberg antiferromagnet KCuF3. It yields the correct description of the relative intensity of the spectral lines in both polarizations E c and E‖c. The magnon density of states has been calculated. The origin of the fine sideband structure in KCuF3 can be explained. The sharp magnon lines, observed in Ref. [1], correspond to the low energy singularities in the magnon density of states.

Abstract: Direct measurements of the magnetocaloric effect (MCE) and magnetization have been conducted for the R(Co1-xAlx)2 (R = Tb, Ho) compounds. It was found that the small substitutions of Co by nonmagnetic Al lead to an increase both of the magnetic ordering temperature and the value of MCE. The following increase in Al content decreases the Curie temperature and the value of MCE. The analyses of the MCE effect is conducted considering the ferrimagnetic structure and the itinerant nature of these compounds.

Abstract: Characteristics of the temperature transformation of magnetic domain structure (DS) during different spin reorientation transitions (SRT) are analyzed on the basis of DS investigations of R2Fe14B, RFe11Ti, RCo5, R2Fe17 single crystals (R = Nd, Gd, Tb, Dy, Ho, Er) in the temperature interval of 4.2 - 400 K.

Abstract: Spin-reorientation transitions in intermetallic (Pr1-xSmx)Fe8Ga3C compounds with the tetragonal BaCd11-type structure have been investigated. The magnetic phase diagram has been proposed for these compounds based on magnetic and X-Ray diffraction studies using their nanocrystalline ribbons and powders aligned in a magnetic field. In the concentration range 0 ≤ x ≤ 0.4 the compounds exhibit an «easy-plane» anisotropy at all temperatures of the magnetically ordered state. The magnetic anisotropy of the compounds with 0.5 ≤ x ≤ 1 is of the «easy-cone» type. The SmFe8Ga3C compound with the highest Sm content is a uniaxial ferromagnet with no indications of a spin-reorientation transition below its Curie temperature.

Abstract: Nucleation processes in phase transitions of a spin-reorientation type in real magnets are examined in the paper. The basic simulation of new-phase nuclei condensing on defects is chosen to be the magnetization distribution corresponding to a 0-degree domain wall. The numeric implementation of the corresponding variation problem for a sample of a finite thickness gives stable states of the considered magnetic heterogeneities and demonstrates that the structure and properties depend mainly on the defect parameters and the sample-quality factor. The obtained dependencies allow describing the behavior of the new-phase nuclei in the vicinity of the spin-reorientation phase transition quite consistently with the experimental data.