Microscopic aspects of spin dynamics in spin ices

Orateur : Tom FENNELL (Laboratory for Neutron Scattering and Imaging, PSI, Switzerland)

Generalities of the description of spin ice materials in terms of a Coulomb phase with emergent magnetic monopole excitations are now quite well known, but important aspects remain to be understood. One such aspect concerns the related questions of how monopoles are created, how they hop across the lattice, and how they are annihilated. Such questions can also be phrased as investigations of spin dynamics and relaxation mechanisms. I will present experimental results concerning spin flipping processes in the rare earth titanate spin ices (Dy2Ti2O7 and Ho2Ti2O7), including investigations of the crystal field levels, phonon band structures, and their coupling ; and investigations of the surprisingly fast dynamics of the spinels CdEr2X4 (X=Se,S), the first spin ices outside the pyrochlore structure, including detailed characterisation of their Coulomb gas parameters and origin of the fast monopole hopping. Along the way I will also briefly discuss magnetoelastic coupling and excitations in the closely related compound Tb2Ti2O7 (in particular a new example of a bound state, or vibron, between crystal field and phonon excitations), as well as other recent activities in the field of frustrated magnetism at PSI.

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