Absence of long-range order in an X Y pyrochlore antiferromagnet Er 2 AlSbO 7

Rare-earth pyrochlores are known to exhibit exotic magnetic phenomena. We report a study of crystal growth and characterizations of a new rare-earth compound ${\mathrm{Er}}_{2}{\mathrm{AlSbO}}_{7}$, in which ${\mathrm{Al}}^{3+}$ and ${\mathrm{Sb}}^{5+}$ ions share the same positions with a random distribution. The magnetism is studied by magnetic susceptibility, specific heat, and thermal conductivity measurements at low temperatures down to several tens of millikelvin. Different from the other reported Er-based pyrochlores exhibiting distinct magnetically ordered states, a spin-freezing transition is detected in ${\mathrm{Er}}_{2}{\mathrm{AlSbO}}_{7}$ below 0.37 K, which is primarily ascribed to the inherent structural disorder. A cluster spin-glass state is proposed in view of the frequency dependence of the peak position in the ac susceptibility. In addition, the temperature and field dependence of thermal conductivity indicates rather strong spin fluctuations which is probably due to the phase competition.