Synthesis and crystal growth

Abstract:

A superconducting ring could be used to simulate the supercurrent conduction, and its interaction with magnetic vortices in a superconducting solenoid, allowing one to investigate the nature of the vortex structure and its pinning in the presence of the persistent supercurrent. The dissipation of the persistent supercurrent has been studied in a ring-shaped high purity single crystal of Bi2 Sr2 CaCu2 Ox in order to obtain the information about the exponent μ, a parameter in the scaling relation between the effective energy barrier against vortex motion U effand the persistent current density J. The measurements of the persistent supercurrent decay show a transition from a strongly nonlogarithmic to a logarithmic decay regime with an increasing temperature. In response to a small increase in the concentration of oxygen vacancies μ decreases in the logarithmic decay regime but remains almost constant in the nonlogarithmic one. © 2010 American Institute of Physics.

Abstract:

We present the results of muon-spin relaxation (μ+ SR) measurements on the hexagonal manganite HoMnO3. Features in the temperature-dependent relaxation rate λ correlate with the magnetic transitions at 76, 38, and 34 K. The highest temperature transition, associated with the ordering of Mn3+ moments has the largest effect on λ. The application of a static electric field of E=5× 106 Vm-1 below T=50K causes a small reduction in λ which is suggestive of coupling between ferroelectric and magnetic domain walls in the ordered state of the material. © 2010 The American Physical Society.

Abstract:

Resonant X-ray scattering measurements have been performed at the (011) Bragg forbidden reflection of YVO3 at the vanadium K-edge. Data were taken above and below the orbital, magnetic and structural transition occurring at 77 K. Energy spectra calculated by the FDMNES code are shown to be in excellent agreement with our experimental data, conclusively showing the signal to originate from anisotropic tensor of susceptibility scattering; ie. solely due to distortions of the lattice and hence the crystal field. We thus resolve the ambiguous origin of the resonant energy spectra in the literature. © 2010 IOP Publishing Ltd.

Abstract:

Controlling orbital occupancy is a fundamental prerequisite for orbitronics. It has been shown in the orthorhombic bilayer manganite Pr(Sr 0.1Ca0.9)2Mn2O7 that the direction of orbital order stripes can be influenced by controlling temperature or through inducing strain in the material. In this paper we have used resonant soft x-ray diffraction at the Mn L-edge to confirm the rotation of the orbital direction TOO2 and furthermore prove that there is no change in the occupied orbital type, however the orbital rotation causes a switch from 3x 2-r2 to 3y2-r2 on a single site. We find that unlike the tetragonal bilayer manganites, where an onset of A-type AFM quenches the orbital order, no such effect is found on the orbital order below TN. © 2010 IOP Publishing Ltd.

Abstract:

The temperature dependence of the magnetic order of stripe-ordered La 1.725Sr0.275NiO4 is investigated by neutron diffraction. Upon cooling, the widths of the magnetic Bragg peaks are observed to broaden. The degree of broadening is found to be very different for l = odd-integer and l = even-integer magnetic peaks. We argue that the observed behaviour is a result of competition between magnetic and charge order. © 2010 IOP Publishing Ltd.