J. Ihringer

Magnetic phase control by an electric field.

The quest for higher data density in information storage is motivating investigations into approaches for manipulating magnetization by means other than magnetic fields. This is evidenced by the recent boom in magnetoelectronics and ‘spintronics’, where phenomena such as carrier effects in magnetic semiconductors and high-correlation effects in colossal magnetoresistive compounds are studied for their device potential. The linear magnetoelectric effect—the induction of polarization by a magnetic field and of magnetization by an electric field—provides another route for linking magnetic and electric properties. It was recently discovered that composite materials and magnetic ferroelectrics exhibit magnetoelectric effects that exceed previously known effects by orders of magnitude, with the potential to trigger magnetic or electric phase transitions. Here we report a system whose magnetic phase can be controlled by an external electric field: ferromagnetic ordering in hexagonal HoMnO3 is reversibly switched on and off by the applied field via magnetoelectric interactions. We monitor this process using magneto-optical techniques and reveal its microscopic origin by neutron and X-ray diffraction. From our results, we identify basic requirements for other candidate materials to exhibit magnetoelectric phase control.

Study of the ferroelectric phase transition of TlGaSe2 by dielectric, calorimetric, infrared and X-ray diffraction measurements

AbstractThe real part of the dielectric constant ε′, the heat capacitycp, the infrared reflectivity, and the X-ray diffraction of TlGaSe2 have been measured in the temperature range from 12 K (30K) to 300 K. Both ε′ andcp show two anomalies at about 110 K and 120 K. A study of the hysteresis loop as well as an investigation of the dielectric dispersion in the microwave region show that the phase below 110 K is ferroelectric. The crystal structure remains nearly unchanged in the course of the phase transition. The loss of the

Crystal structure of the ceramic superconductor BaPb0.75Bi0.25O3

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Monoclinic symmetry in LaSrCu0.5Co0.5O4−z found by neutron, Guinier-and synchrotron-X-ray powder structure analysis

symmetry (C2/c→Cc) results from small positional shifts of the T1 atoms in the ab plane accompanied by a discontinuity in the axial ratios. We suggest, that the ferroelectricity is caused by the stereochemically active electron lone pair configuration of the Tl+ ion. Thus TlGaSe2 may provide the first example for ferroelectricity caused by this mechanism.

Low pressure and temperature dependent phase transitions of a potassium exchanged zeolite A

AbstractThe structure of the distorted perovskite BaPbO3 was studied with high-resolution X-ray diffraction at 300 K and 26 K and with neutron diffraction at 300 K. Simultaneous refinement of the neutron and X-ray data sets (300 K) using the Rietveld method yields a monoclinic structure with the space groupI 2/m and lattice parametersa=6.0278 (1) Å,b=6.0664(1) Å,c=8.5109(1) Å, and γ=90.083 (2)o. The tilting of the oxygen octahedra is given asa−a−c0 in Glazers notation [11]. The monoclinic angle corresponds to the angle between the cubic directions [110]c and

Structural study of the Na5W3O9F5 phase transitions by X-ray and neutron diffraction

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