Ho2Ge2O7 and Pr2Zr2O7: a tale of two spin ices
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The spin ice state is a rare magnetic ground state that can be observed in the pyrochlore oxides, A2B2O7. In this ground state, the spins, align such that two spins point inwards and two outwards on each tetrahedron. The emergence of monopole-like excitations in spin ices has given rise to immense interest in this class of materials. However, a complex set of conditions must be met for a material to adopt the spin ice state, making them exceedingly rare. Prior theoretical studies have put forth two pyrochlores, Ho2Ge2O7 and Pr2Zr2O7, as spin ice candidates. The aim of this project was to fully characterize these compounds and determine their magnetic ground states. We show through magnetometry, heat capacity, and neutron scattering that Ho2Ge2O7 is a new, highly correlated spin ice material. Conversely, Pr2Zr2O7, while exhibiting many spin ice properties, has a ground state which remains undetermined.