Solid State Phenomena Vols. 233-234

Abstract: The rotation and translational motion of the samples with a magnetizable material alonga bottom of a vessel in a uniform applied rotating magnetic field are examined experimentally. Weconsider a magnetic fluid (MF) drop and a body with a magnetizable polymer (MP). The phenomenaof the change of the direction of the translation motion at some field frequency is observed only forthe MF drop.

Abstract: The present paper focuses on the magnetoelectric coupling in dimensionally graded ferrite-piezoelectric bilayers in the electromechanical resonance region. Using the bilayer as a transducer which converts the ac magnetic field into an ac electric field shows that the transmission coefficient equals approximately -83 dB for zero bias magnetic field and -44 dB for bias field of 340 Oe. Thus, applying the DC field enables one to obtain the transmission coefficient variation range of 39 dB for the investigated structure. The phenomenon is of importance for the realization of multifunctional magnetoelectric devices including sensors and transducers operating at microwave frequencies.

Abstract: This manuscript is devoted to the magnetoelectric coupling in a dimensionally graded magnetostrictive-piezoelectric structure in the electromechanical resonance region. Theoretical frequency dependence of ME voltage coefficient is obtained. Theoretical estimates for the layered structure of lead zirconate-titanate and single-crystal Zn_0,3Ni_0,7Fe₂O₄ are in satisfactory agreement with data. The obtained results are expected to facilitate observation of enhanced ME coupling at overlapping of electromechanical and magnetic resonance due to energy transfer between spin waves and phonons.

Abstract: Temperature characteristics of resonant magnetoelectric effect in bilayer structures consisting of langatate, lead zirconate titanate, nickel, and amorphous ferromagnetic Metglas layers have been investigated. The measurements were performed in the temperature range of 150-400 K. The influence of the ferromagnetic and piezoelectric layer’s parameters on the temperature dependence of resonant frequency and magnetoelectric coefficient α_E has been demonstrated. The results can be used to develop magnetoelectric magnetic field sensors.

Abstract: The magnetic properties of trigonal Pr_xY_1-xFe₃(BO₃)₄ compound have been investigated. Anomalies on the magnetization curves induced by a magnetic field are observed for each composition. 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 Pr_xY_1-xFe₃(BO₃)₄ have been interpreted and good agreement between theory and experiment has been achieved.

Abstract: We have investigated temperature-dependent magnetic hysteresis loop behavior of Ba_2-xLa_xFeMoO₆ with double perovskite structure by means of a vibrating sample magnetometer (VSM). As partial substitution of Ba²⁺ by La³⁺ is varied from x = 0.1 to 0.3, T_C is found to increase from 324 to 345 K. Interestingly, however, hysteresis loop area, remanent magnetization, and coercivity are found to follow a universal behavior with respect to a temperature variation regardless of the Ba²⁺ substitution.

Abstract: Sm_1-xLa_xFe₃(BO₃)₄ (х = 0, 0.5, and 0.75) single crystals are grown by the flux method and their characteristics are investigated in the temperature range 5−300 K and magnetic fields of up to 9 T. It is established that substitution of nonmagnetic La³⁺ ions for magnetic Sm³⁺ ions increases the magnetic moment and weakens the magnetoelectric effect in Sm_1-xLa_xFe₃(BO₃)₄.

Abstract: Multiferroic composites of (x)NiFe₂O₄ + (1-x)BaTiO₃ with x = 0.2, 0.3 and 0.4 and (x)CoFe₂O₄ + (1-x)BaTiO₃ with x = 0.2, and 0.4 have been synthesized by mixing NiFe₂O₄ (CoFe₂O₄) spinel and BaTiO₃ piezoelectric. Distribution of Ni (Co) ions on 8a and 16d positions of spinel lattice (space group F d-3m) is determined by neutron powder diffraction. Wave vector of magnetic structure of the spinel is k = 0. The dielectric permittivity of the composites was measured for the frequency range 10² – 10⁵ Hz. At low frequencies the dielectric permittivity decreased from ~940 for x = 0.2 to ~360 for 0.4.

Abstract: Charge ordering of nonstoichiometric LuFe₂O_4+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.

Abstract: Properties of two dimensional multiferroic with magnetic and electric order was studied on two-dimensional lattice with size 20x20. As a result of modeling was found temperature dependencies of polarization, magnetization and dielectric, magnetic and magnetoelectric susceptibilities for different values of magnetoelectric coefficients. Modeling shows influence of external fields on phase transitions through magnetoelectric effect. Magnetoelectric coupling leads to shift in temperature of phase transition.