Magnetization and susceptibility studies on single crystals of the pyrochlore ${\mathrm{Ho}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ are reported. Magnetization isotherms are shown to be qualitatively similar to that predicted by the nearest-neighbor spin-ice model. Below the lock-in temperature, $T^{*}\simeq 1.97\hspace{0.5em}\mathrm{K},$ magnetization is consistent with the locking of spins along $\left[111\right]$ directions in a specific two-spins-in, two-spins-out arrangement. Below $T^{*}$ the magnetization for $B||\left[111\right]$ displays a two step behavior signaling the breaking of the ice rules.

• Received 18 May 2001

DOI:https://doi.org/10.1103/PhysRevB.64.060406