Events in Physics
Jason Gardner
Recent neutron scattering results from geometrically frustrated magnets
Using polarised neutron diffraction, inelastic neutron scattering and neutron spin echo I have studied the spin-spin correlations in several geometrically frustrated magnets. One sample of particular interest is Gd2Sn2O7. It is thought to be a good approximation to a Heisenberg antiferromagnet on a pyrochlore lattice with exchange and dipole-dipole interactions. Theoretically such a system is expected to enter a long range ordered ground state known as the ‘Palmer Chalker’ state [1]. We show conclusively, through neutron scattering data, that the system indeed enters an ordered state with the Palmer-Chalker spin configuration below Tc = 1 K. Within this state we have also observed gapped spin waves. I will compare these results to the isostructural Gd2Ti2O7 and Tb2Sn2O7 compounds. Gd2Ti2O7 has two magnetic transitions but never completely freezes [2]. Tb2Sn2O7 also enters a partially ordered state that is characterized as a two-sublattice ferrimagnetic state which coexists with a paramagnetic spin component [3].
[1] S. E. Palmer and J. T. Chalker, Phys. Rev. B 62, 488 (2000).
[2] J. R. Stewart, G. Ehlers, A. S. Wills, S. T. Bramwell, and J. S. Gardner,
J. Phys.:Condens. Matter 16, L321 (2004).
[3] K. Rule et al., Phys. Rev. B. 76, 212405 (2007).