Dy2ScNbO7: a study of the effect of a disordered B-site on the spin ice magnetism typically seen in dysprosium pyrochlores

Abstract

The thermodynamics of disorder have been studied for hundreds of years, with physicists using entropy to quantitatively connect the macroscopic properties of a system to its microscopic multiplicity (disorder). Here, we consider the effect of disorder in magnetic materials. The pyrochlore oxides (A2B2O7), comprised of a bipartite lattice of corner-sharing tetrahedra, have been central to the study of geometric frustration for the past several decades. Pyrochlores, in which the A-site is occupied by the magnetic cation dysprosium, tend to exhibit spin ice ordering down to low temperatures, in spite of chemical perturbations to the B-site lattice. With the motivation of this study being the investigation of how adding B-site disorder to the traditional Dy2ScNbO7 form of Dy-pyrochlores, a stoichiometric mixture of Sc-3+ and Nb-5+ was used to synthesize Dy2ScNbO7, the pyrochlore material that is central to this thesis work. We show using magnetometry, heat capacity, muon spin relaxation, and inelastic neutron scattering that the mixed B-site pyrochlore Dy2ScNbO7, does not adopt the spin ice ground state. The low temperature spin dynamics are much faster than other analogous dysprosium pyrochlores, the residual entropy is significantly smaller than that predicted for a spin ice and there are low-lying crystal field excitations. These results all indicate that the B-site disorder appears to destroy the predicted Ising anisotropy of dysprosium.