Bulk magnetization of the heavy rare earth titanate pyrochlores - a series of model frustrated magnets

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Abstract
We describe magnetization measurements on the heavy rare earth titanate pyrochlores R2 Ti2 O7 , where R = Gd, Dy, Ho, Er, Yb, in the temperature range 1.8-300 K, and the field range 0-70 000 Oe. In these materials magnetism arises from the rare earth ions, while Ti is non-magnetic. Analysis of the low field susceptibility versus temperature curves shows that Gd2 Ti2 O7 has antiferromagnetic coupling ( -9 K), which suggests that it is an example of a frustrated antiferromagnet on the pyrochlore lattice. Er2 Ti2 O7 is likewise found to have a large negative Curie-Weiss temperature, -22 K, which we argue is indicative of antiferromagnetic coupling. Ho2 Ti2 O7 , Dy2 Ti2 O7 and Yb2 Ti2 O7 are found to have weak ferromagnetic coupling ( 2 K, 1 K and 1 K respectively) which may be largely dipolar in origin. Fitting of the high field magnetization versus field curves suggests a strong 1,1,1 single ion anisotropy that identifies these three materials as possible realizations of the ferromagnetic `spin ice' model.