Solid State Phenomena Vol. 190

Abstract: The structure and properties of SrFe₁₂O₁₉ powders, which were produced by mechanical activation followed by annealing and had a nanocrystalline structure, were studied. The powders prepared exhibit a high coercive force μ₀H_ci=0.40-0.45 Т. The substantially higher coercive force (up to 0.75-0.82 T) was typical to SrFe₁₂O₁₉ powders produced by oxide-glass crystallization. Nanostructured materials comprising Fe₃O₄ and Fe phases with crystallite sizes of 10-30 nm are shown can be prepared from Fe₂O₃+Fe, Fe₂O₃+Fe+Co and FeO+Co powder mixtures by mechanochemical technique followed by annealing. These nanomaterials have the hard magnetic properties and their coercive force reaches μ₀H_ci 0. 08 T.

Abstract: For the first time the rearrangement of cerium local environment in Ce2Fe17-xMnx(x = 0; 1; 2) intermetallics vs. Mn concentration and temperature was investigated by thespectroscopy of extended X-ray absorption fine structure (EXAFS) above K-Ce absorptionedge. At the same time under similar conditions by the spectroscopy of X-ray absorption near-edge structure (XANES) above L3-Ce absorption edge the valence state of Ce was studied. Thecorrelation is found between changes in local electronic and crystalline structure observed inCe2Fe17-xMnx and the types of magnetic states in these compounds.

Abstract: The spectrum of coupling spin and electromagnetic waves for magnetic having spiral magnetic structure defined by non-uniform exchange and relativistic interactions have been received. The possibility of resonant interaction of spin and electromagnetic waves has been shown. The electromagnetic waves reflectance for the layer of magnetic having ferromagnetic spiral has been calculated for different angles of spiral.

Abstract: The magnetic properties of trigonal Nd_0.6Dy_0.4Fe₃(BO₃)₄ substituted compound with the competitive Nd-Fe and Dy-Fe exchange interactions have been investigated. It has been shown that in Nd_0.6Dy_0.4Fe₃(BO₃)₄ a spontaneous spin-reorientation transition from an ease-axis state to an easy-plane occurs near 31 K. Anomalies of the magnetization curves are observed in a spin-flop transition induced by the magnetic field B||c. The calculations were performed using a molecular-field approximation and a crystal-field model for the rare-earth subsystem. Extensive experimental data on the magnetic properties of Nd_0.6Dy_0.4Fe₃(BO₃)₄ have been interpreted and good agreement between theory and experiment has been achieved using the obtained theoretical dependences.

Abstract: The influence of magnetoelectric interactions on the magnetic structure, flexomagnetoelectric polarization and magnetization in thin multiferroics film has been investigated. The correlation between antiferromagnetic domain structure and ferroelectric domain pattern has been revealed. It has been shown the asymmetry of the antiferromagnetic vector distribution over multiferroics film in the case of 109⁰ and 71⁰ ferroelectric domain walls. The direction of spins rotation in magnetic domain walls is determined by the type of ferroelectric domains and the antiferromagnetic vector in the centre of ferroelectric domain. The peculiarities of the micromagnetic distribution are reflected in the behavior of polarization and magnetization, which appears to be different for 180⁰, 109⁰ and 71⁰ ferroelectric domains.

Abstract: Various resonance modes were observed in the transmission spectra of rare-earth iron borates RFe₃(BO₃)₄ (R = Nd³⁺, Sm³⁺, Gd³⁺) at the frequency range 100-600 GHz, which were attributed to collective magnetic excitations in the exchange coupled Fe-and R-subsystems, i.e. antiferromagnetic (Fe) resonance and electron transitions in the R-ions. Strong interaction of the Fe and R oscillations was revealed and theoretically analyzed taking into account feature of the R-ion ground state. Intensities of the coupled modes (contributions to magnetic permeability) strongly depend on a difference of Fe and R ions g-factors that allows defining the sign of the latter. In particular, an appreciable intensity of exchange (Nd) modes in NdFe₃(BO₃)₄ is caused by g^Nd_,|| < 0 whereas in GdFe₃(BO₃)₄ with g_Gd g_Fe 2 the exchange (Gd) modes were hided due to compensation of Fe and Gd contributions. In SmFe₃(BO₃)₄, despite a negligible Sm g-factor, the Sm modes were clear observed due to their excitation via coupling with the Fe-subsystem.

Abstract: The optical properties of single crystals of the hexagonal manganites RMnO₃ (R = Ho, Tm, Yb) have been investigated by spectroscopic ellipsometry in the spectral range 0.6-5.0 eV. The measurements show a strong anisotropy of the diagonal elements of the dielectric tensor. It has been demonstrated that the optical absorption edge for the polarization Ec was determined by the intense band of O(2p)Mn (3d) transition centered near 1.6 eV, whereas this band for the polarization Ec was strongly suppressed and shifted toward higher energies by 0.15-0.20 eV. The spectral dependences of the ε₁(E) and ε₂(E) for HoMnO₃, TmMnO₃ and YbMnO₃ single crystals were qualitatively similar. The broad absorption band at E<1.0 eV clearly appears at the energies below the fundamental absorption edge of all of study compounds. It is possible, the origin of the near-infrared ε₂(E) absorption is associated with 4f-4f transitions of R³⁺ ions.

Abstract: Physical properties of oxides RMn2O5 (R-rare earth ion) have intensively been studied for the last 15 years. Lately, an increased attention has been drawn to such systems in connection with the discovery in them of a strong relation between long magnetic order and electrical polarization.

Abstract: A model is discussed here for the resonance enhancement of magnetoelectric (ME) interactions in ferrite-piezoelectric bilayers at frequencies corresponding to bending oscillations. The thickness dependence of stress, strain and magnetic and electric fields within the sample are taken into account so that the bending deformations could be considered in an applied magnetic or electric field. The boundary conditions corresponding to bilayers that are free to vibrate at both ends, or simply supported at both ends, or fixed at one end are considered. The explicit expressions for ME voltage coefficients are derived by way of exact solution of electrostatic, magnetostatic and elasto-dynamic equations for thin plate and disk-shaped bilayers. The model is applied to a specific case of nickel and lead zinconate titanate (PZT) bilayer. Theoretical ME voltage coefficients versus frequency and PZT to nickel thickness ratio profiles are in excellent agreement with data.

Abstract: We report on possible types of spatially modulated antiferromagnetic structures in the biaxial multiferroic and their stability depending on the ratio of the magnetic anisotropy and flexomagnetoelectric interaction parameters.