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

We describe magnetization measurements on the heavy rare earth titanate pyrochlores R(2)Ti(2)O(7), 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 held susceptibility versus temperature curves shows that Gd(2)Ti(2)O(7) has antiferromagnetic coupling (theta approximate to -9 K), which suggests that it is an example of a frustrated antiferromagnet on the pyrochlore lattice. Er(2)Ti(2)O(7) is likewise found to have a large negative Curie-Weiss temperature, theta approximate to -22 K, which we argue is indicative of antiferromagnetic coupling. Ho(2)Ti(2)O(7), Dy(2)Ti(2)O(7) and Yb(2)Ti(2)O(7) are found to have weak ferromagnetic coupling (theta approximate to 2 K, 1 K and 1 K respectively) which may be largely dipolar in origin. Fitting of the high held 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.