Andrew Boothroyd

Abstract:

Polarized neutron inelastic scattering has been used to measure spin excitations in ferromagnetic La0.82Sr0.18CoO3. The magnon spectrum of these spin excitations is well defined at low energies but becomes heavily damped at higher energies and can be modeled using a quadratic dispersion. We determined a spin wave stiffness constant of D=94±3 meV Å2. Assuming a nearest-neighbor Heisenberg model we find reasonable agreement between the exchange determined from D and the bulk Curie temperature. Several possible mechanisms to account for the observed spin-wave damping are discussed. © 2010 The American Physical Society.

Abstract:

We report the direct measurement of antiferromagnetic spin polarization at the oxygen sites in the multiferroic TbMn2O5, through resonant soft x-ray magnetic scattering. This supports recent theoretical models suggesting that the oxygen spin polarization is key to the magnetoelectric coupling mechanism. The spin polarization is observed through a resonantly enhanced diffraction signal at the oxygen K edge at the commensurate antiferromagnetic wave vector. Using the fdmnes code we have accurately reproduced the experimental data. We have established that the resonance arises through the spin polarization on the oxygen sites hybridized with the square based pyramid Mn3+ ions. Furthermore we have discovered that the position of the Mn3+ ion directly influences the oxygen spin polarization.