Dr Dharmalingam Prabhakaran

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.

Abstract:

We report on the extension of resonant magnetic diffraction into the soft X-ray region (500-1500eV). We conducted soft X-ray diffraction from a bulk single crystal of La2-2xSr1+2xMn2O7 using an in-vacuum diffractometer. We demonstrate that the resonant enhancement diffraction of the (001) magnetic peak at the manganese L-III and L-II absorption edges is extremely large. Measurements taken on samples with different strontium dopings demonstrate that the shape of the energy resonance is also dependent on the sample stoichiometry. We have applied this technique to the study of other materials such as UAs1-xSex where incommensurate magnetic diffraction has been observed at the uranium N-IV and N-V edges. (C) 2003 Elsevier B.V. All rights reserved.

Abstract:

We report magnetization and neutron scattering measurements of the half-doped compound La1.5Sr0.5CoO4, which exhibits a checkerboard pattern of charge ordering below not, vert, similar800 K. In the antiferromagnetically-ordered phase below not, vert, similar40 K the spins are found to be canted in the ab plane. The spin excitation spectrum includes spin-wave excitations with a maximum energy of 16 meV, and diffuse magnetic modes at energies around 30 meV.