No abstract

No abstract

Abstract-Magnetic field and temperature dependencies of the critical current density, ( ) were measured by SQUIDmagnetometry, ac magnetic susceptibility, and dc transport current techniques in the single-crystalline epitaxially-grown by offaxis dc magnetron sputtering YBa 2 Cu 3 O 7 (YBCO) films with ( 77 K) 2 10 6 A/cm 2 . The mechanism of vortex depinning from growth-induced linear defects, i.e., out-of-plane edge dislocations in low-angle tilt domain boundaries, is shown to describe quantitatively measured (). The developed model takes into account a statistical distribution of the dislocation domain boundaries ordered in a network as well as the interdislocation spacing within boundaries. Actual structural features of YBCO film known from HREM data turn out to be extracted from ( )-curves by a fitting procedure within the proposed model.

Magnetic properties of a magnetoactive elastomer (MAE) filled with µm-sized soft-magnetic iron particles have been experimentally studied in the temperature range between 150 K and 310 K. By changing the temperature, the elastic modulus of the elastomer matrix was modified and it was possible to obtain magnetization curves for an invariable arrangement of particles in the sample as well as in the case when the particles were able to change their position within the MAE under the influence of magnetic forces. At low (less than 220 K) temperatures, when the matrix becomes rigid, the magnetization of the MAE does not show a hysteresis behavior and it is characterized by a negative value of the Rayleigh constant. At room temperature, when the polymer matrix is compliant, a magnetic hysteresis exists and exhibits local maxima of the field dependence of the differential magnetic susceptibility. The appearance of these maxima is explained by the elastic resistance of the matrix to the displacement of particles under the action of magnetic forces.

Strong effects of optical polarization anisotropy observed previously in the quantum wells subjected to the in-plane magnetic field arrive at complete description within microscopic approach. Theory we develop involves two sources of optical polarization. First source is due to correlations between electron and heavy hole (HH) phases of ψ-functions arising due to electron Zeeman spin splitting and joint manifestation of low-symmetry and Zeeman interactions of HH in an in-plane magnetic field. In this case, four possible phase-controlled electron-HH transitions constitute the polarization effect, which can reach its maximal amount ( ±1) at low temperatures when only one transition survives. Other polarization source stems from the admixture of excited light-holes (LH) states to HH by low-symmetry interactions. The contribution of this mechanism to total polarization is relatively small but it can be independent of temperature and magnetic field. Analysis of different mechanisms of HH splitting exhibits their strong polarization anisotropy. Joint action of these mechanisms can result in new peculiarities, which should be taken into account for explanation of different experimental situations.

The ability to controllably tune the heating efficiency of magnetic nanoparticles in an AC magnetic field is highly desirable for their application as mediators of magnetic hyperthermia. Traditional approaches to understand and govern the behavior of hyperthermia mediators include a combination of quasistatic and high-frequency (∼100 kHz) magnetic measurements with subsequent simulation of underlying processes. In this paper, we draw attention to the frequently overlooked fact that for an ensemble of magnetic nanoparticles, there is no straightforward complementarity between the dynamic characteristics obtained under different experimental conditions, as well as between corresponding underlying processes. This paper analyzes mechanisms of AC losses in a fluid based on magnetic nanoparticles, with special emphasis on the domains of their validity, and shows that the mechanisms may become qualitatively different as experimental conditions change from magnetostatic to high-frequency ones. Further, the work highlights new important features which can result from the employment of the refined approaches to interpret experimental results obtained on magnetic fluids based on La1-xSrxMnO3 (x = 0.22) nanoparticles. The gained knowledge provides necessary guidelines for tailoring the properties of magnetic nanoparticles to the needs of self-controlled magnetic hyperthermia.

No abstract

A model for the limiting of the critical current in rather perfect high-Tc superconducting crystals and epitaxial films with a block structure with small angles of misorientation θ of the crystalline blocks is considered for the case when the distance d between edge dislocations along the boundary between blocks is greater than the coherence length ξ(T). It is shown that under these conditions the transparency of low-angle boundaries for the superconducting current carriers near the critical temperature Tc is practically independent of θ and T. As a result, the only factor governing the temperature dependence of the critical current density jc(T) remains the depairing current j0(T)∝(1−T/Tc)3/2. Near Tc, when ξ(T)>d, a transition from the dependence jc(T)∼(1−T/Tc)3/2 to a dependence jc(T)∼(1−T/Tc)2 occurs. This behavior of jc(T) is in good agreement with the results of experimental measurements of the critical currents in thin epitaxial films of YBa2Cu3O7−δ.