When a magnetic field is applied to a single crystal of magnetite at 124 K > T > 50 K, the monoclinic c M axis, which is the easy magnetization axis, switches to one of the 100 cubic directions, nearest to the direction of the magnetic field, and the phenomenon known as an axis switching (AS) occurs. A global symmetry probe, resonant x-ray scattering, and a local probe, Mössbauer spectroscopy, are used to better understand the mechanism of axis switching. The behavior of three subsystems ordered below the Verwey transition temperature T V , i.e., lattice distortion, an orbital, and charge orderings, was observed via resonant x-ray scattering as a function of an external magnetic field. This was preceded by calculation of selected peak intensities using the FDMNES code. The Mössbauer spectroscopy studies confirmed that the magnetic field triggers electronic rearrangements and atomic displacements. The structure observed after the process of axis switching is very similar to the one obtained after cooling below T V with the magnetic field applied along one of the initial 100 cubic directions and distinct from the cooling in the absence of a magnetic field. From all the experimental observations of the phenomenon done so far, it is clear that AS starts from the fluctuations between octahedral iron orbitals that ultimately lead to the Verwey transition, but also to the higher-temperature trimeron dynamics. Therefore, further observation of the axis switching may be a key point to the understanding of a majority of strongly correlated electronic behavior in magnetite as well as in other transition metal oxides.
The (Bi 1−x Pb x) 2 Sr 2 Ca 2 Cu 3 O y (x = 0.2, 0.4) films were obtained directly on silver substrates by the sedimentation process. The temperature dependencies of the AC susceptibility of the films and bulk materials were measured and analyzed. The critical temperatures of the grains T cg as well as the Josephson junctions T cJ of these films were obtained from the dispersion part of AC susceptibility and they are T cg = 106.5 K, T cJ = 100.2, T cg = 106.1 K, and T cJ = 97 K, respectively. The thickness of these films is of the order of a hundred micrometers. The critical currents were derived from the absorption part of AC susceptibility using the Bean's critical state model. The temperature dependencies of the critical currents were analyzed using the Ginzburg-Landau strong coupling limit approach.
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