Andrew Boothroyd

Abstract:

We report magnetization measurements on La2-xSrxNiO4+delta single crystals, with 0less than or equal toxless than or equal to0.5. Glassy behaviour associated with the formation of spin-charge stripes, and a separate spin-glass phase at low temperatures were observed. We have also found a 'memory effect' in the magnetic field-temperature history, which is found to be suppressed in the low-temperature spin state of the x = 0.333 crystal. (C) 2003 Elsevier B.V. All rights reserved.

Abstract:

We report neutron scattering measurements of the spectrum of magnetic excitations in the stripe-ordered phase of La2-xSrxNiO4 (x = 0.275 and 1/3). The propagating spin excitations follow a similar dispersion relation for the two compositions, but the line widths are broader for x = 0.275 than for 1/3. (C) 2003 Elsevier B.V. All rights reserved.

Abstract:

We have studied magnetic correlations in several compositions of stripe-ordered La2-xSrxNiO4. In this paper we show how polarized-neutron scattering has helped uncover important features of the magnetic ordering and spin dynamics. In particular, polarization analysis has enabled us (1) to characterize a spin reorientation transition, (2) to identify anisotropy gaps in the spin excitation spectrum and (3) to investigate an anomalous dip in the spin-wave intensity suggestive of coupling between collective spin and charge excitations. (C) 2003 Elsevier B.V. All rights reserved.