Spin Correlations inHo2Ti2O7: A Dipolar Spin Ice System

Abstract

The pyrochlore material ${\mathrm{Ho}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ has been suggested to show “spin ice” behavior. We present neutron scattering and specific heat results that establish unambiguously that ${\mathrm{Ho}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ exhibits spin ice correlations at low temperature. Diffuse magnetic neutron scattering is quite well described by a nearest neighbor spin ice model and very accurately described by a dipolar spin ice model. The heat capacity is well accounted for by the sum of a dipolar spin ice contribution and an expected nuclear spin contribution, known to exist in other ${\mathrm{Ho}}^{3+}$ salts. These results settle the question of the nature of the low temperature spin correlations in ${\mathrm{Ho}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ for which contradictory claims have been made.