Andrew Boothroyd

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.

Abstract:

We present ultrafast resonant soft-x-ray diffraction measurements of time-dependent orbital order in the single-layer-manganite La0.5Sr1.5MnO4. These experiments reveal the appearance of a metastable phase with reduced ordering, different from any thermal state of the system. © OSA / UP 2010.