Фазовый состав и структура пленки BiFeO-=SUB=-3-=/SUB=-, выращенной на подложке MgO(001) методом ВЧ-катодного распыления в атмосфере O-=SUB=-2-=/SUB=-

The crystal structure and Mossbauer spectroscopy studies results for BiFeO3 film growth on the MgO(001) single crystal substrate are present in the paper. It been shown that film have high crystal perfection and low defectiveness which results in appearing of narrow lines during the θ-2θ and φ scanning and the small (lower than 0.7°) disorientation of film and substrate crystal axes. It is been revealed that unit cell of BiFeO3/MgO(001) heterostructure possess monoclinic symmetry and deformation of unit cell is negligible. The Mossbauer study shows that magnetic subsystem of film has spatial spin-modulated structure with zero value of anharmonicity parameter (m). This indicate that at room temperature the magnetic anisotropy changes from the "easy axis" type to "easy plane" type.

Features in the Resonance Behavior of Magnetization in Arrays of Triangular and Square Nanodots

Collective modes of the gyrotropic motion of a magnetic vortex core in ordered arrays of triangular and square ferromagnetic film nanodots have been theoretically investigated. The dispersion relations have been derived. The dipole–dipole interaction of the magnetic moments of the magnetic vortex cores of elements has been taken into account in the approximation of a small shift from the equilibrium position. It is shown that the effective rigidity of the magnetic subsystem of triangular elements is noticeably higher than that of the subsystem of square elements of the same linear sizes. The potential application of the polygonal film nanodisks as nanoscalpels for noninvasive tumor cell surgery is discussed

Improving the Force and Time Response of a DC Solenoid Electromagnetic Actuator by Changing the Lower Core Angle

The aim of almost any electromagnetic actuator development is to increase the electromagnetic force with which an actuator acts on a plunger with as fast a time response as possible while maintaining the dimensions as small as possible. This paper presents research on the impact of the lower core angle on the force and time response of a DC solenoid electromagnetic actuator. The research method is based on the analytical analysis of the magnetic path of the DC solenoid electromagnetic actuator and a comparison with the numerical simulation results. A transient numerical simulation was performed on a 2D axial-symmetric model of the electromagnetic actuator and included simultaneously solving time-dependent partial differential equations of the electromagnetic actuator’s magnetic, electrical, and mechanical subsystems. The magnetic subsystem was analyzed by the finite element method (FEM) using the ANSYS Electronics software package. The three prototype models with different lower core angles were produced and tested in the accredited Laboratory Center of KONČAR Electrical Engineering Institute. The obtained measurements are compared with the analytical results and numerical simulation results.

Electrophysical Properties of PMN-PT-Ferrite Ceramic Composites

Ferroelectromagnetic composites based on (1−x)PMN-(x)PT (PMN-PT) powder and Ni-Zn ferrite powder were obtained and are described in this work. As a ferroelectric component, we used (1−x)PMN-(x)PT solid solution (with x = 0.25, 0.28, 0.31, 0.34, 0.37, 0.40), synthesized using the sol-gel method. As a magnetic component, we used nickel-zinc ferrite, obtained using classic ceramic technology. The six compositions of PMN-PT used have rhombohedral symmetry, tetragonal one and mixture of these phases (morphotropic phase area), depending on x. The final ceramic composite samples were obtained using the classic methods involving the calcination route and pressureless final sintering (densification). The properties of the obtained ceramic composite samples were investigated, including microstructure SEM (scanning electron microscope), dielectric properties, electromechanical properties, and DC (Direct Current) electrical conductivity. Results showed that the microstructures of the PP-F composite samples characterized by larger grains were better crystallized, compared with the microstructures of the PMN-PT ceramic samples. The magnetic properties do not depend on the ferroelectric component of the composite samples, while the insertion of ferrite into the PMN-PT compound reduces the values of remnant and spontaneous polarization, as well as the coercive field. The dielectric measurements also indicated that the magnetic subsystem influences the dielectric properties. The present results show that the PP-F ceramic composite has good dielectric, magnetic, and piezoelectric properties, which predisposes this type of material to specific applications in microelectronics and micromechatronics.

Dynamics of Magnetization in Multilayer TbCo / FeCo Structures under the Influence of Femtosecond Optical Excitation

The need to study ultrafast processes in magnetism is due to the prospects for creating ultrafast magnetic recording and ultrafast spintronic devices. In order to excite the magnetic subsystem femtosecond optical pulses are used. The excitement is manifested as in spin precession. In metals, the material is heated first due to significant optical absorption, and significant Joule losses occur. The most important task is to search for materials in which spin processes are excited without heating. Obvious candidates are weakly absorbing materials, such as ferrite garnets. However, the range of such materials and the range of their functionality are limited.The purpose of this work is to study the dynamics of systems with nonthermal mechanisms of spin precession excitation. Such excitation is possible in ferromagnetic / antiferromagnetic heterostructures with exchange interaction, provided that the recombination time of photocarriers is shorter than the time of heat diffusion. Multilayer TbCo / FeCo structures of the near IR range were investigated for a femtosecond optical pulse. The spin dynamics are compared with the direction of the wave vector of the exciting pulse along and perpendicular to the axis of easy magnetization of the structures (“easy axis” and “hard axis” geometry, respectively). It is shown that in case of “easy axis” geometry the determinative mechanism is the thermal interaction. When the system is exposed to an excitation pulse, this mechanism leads to a decrease in the projection of magnetization on the direction of propagation of the test beam. In case of “hard axis” geometry, the magnetization turns to the magnetic field at the initial stage. Then it precesses and relaxes to an equilibrium angular orientation. Such dynamics indicate a rapid recovery of the uniaxial anisotropy field after laser irradiation. The presented results demonstrate an ultrafast change in the magnetic anisotropy induced during the fabrication of the heterostructure under study, which may be of interest for optical control of the orientation of the magnetization.

Anharmonic phonon properties in Eu0.5Ba0.5TiO3

Phonon properties have been studied using reduced sound velocity of Eu0.5Ba0.5TiO3 (EBTO). To achieve this aim, the anharmonic phonon-phonon interaction and the spin-phonon interaction were used. It was shown that the reduced sound velocity of multiferroic EBTO exhibits a kink at TN = 1.9 K. This anomalously reduced sound velocity can be interpreted as an effect of vanishing magnetic ordering above TN. What’s more, the ferroelectric subsystem cannot be influenced by the magnetic subsystem above TN for TN ≪TC in the EBTO. It was found that the reduced sound velocity decreases as T increases near ferroelectric transition TC. That is to say, the sound velocity softens near ferroelectric transition TC. It is also noteworthy that the reduced sound velocity softens when the RE (the coupling between the ferroelectric pseudo-spins and phonons), V(3) and |V(4)| (the third- and fourth-order atomic force constants of the anharmonic phonons, respectively) increase. These conclusions are all in good accordance with the experimental data and theoretical results.

Магнитокалорический эффект и магнитострикция в сплаве Гейслера Ni-=SUB=-49.3-=/SUB=-Mn-=SUB=-40.4-=/SUB=-In-=SUB=-10.3-=/SUB=- в переменных магнитных полях

The magnetocaloric effect (MCE) and the magnetostriction in the Ni_49.3Mn_40.4In_10.3 Heusler alloy have been measured in ac magnetic fields to 8 T. It is shown that the contributions of the magnetic and structural subsystems to MCE have opposite signs; in this case, the contribution of the magnetic subsystem is dominant. The anomalous temperature dependence of the magnetostriction during the magnetostructural phase transition (PT) is explained by competition of the processes of growing austenite phase nuclei and the striction processes in them.

Quantum effects in magnetotransport of InGaAs quantum wells with remote Mn impurities

We have studied magnetoresistance and Hall effect of GaAs/InxGa1−xAs quantum wells with remote Mn impurity. Temperature and magnetic field dependencies of samples resistivity indicate several effects related to the magnetic subsystem. Shubnikov - de Haas oscillations indicate the presence of several types of regions in conduction channel with significantly different hole mobilities. We discussed the impact of magnetic impurities on quantum corrections to conductivity by comparing our results with the data for similar non-magnetic structures. Our results suggest that the presence of Mn atoms leads to the damping of quantum corrections in in the investigated structures.