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

Abstract

We describe magnetization measurements on the heavy rare earth titanate pyrochlores R2Ti2O7, where R = Gd, Dy, Ho, Er, Yb, in the temperature range 1.8-300 K, and the field range 0-70000 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 Gd2Ti2O7 has antiferromagnetic coupling (θ ≈ -9 K), which suggests that it is an example of a frustrated antiferromagnet on the pyrochlore lattice. Er2Ti2O7 is likewise found to have a large negative Curie-Weiss temperature, θ ≈ -22 K, which we argue is indicative of antiferromagnetic coupling. Ho2Ti2O7, Dy2Ti2O7 and Yb2Ti2O7 are found to have weak ferromagnetic coupling (θ ≈ 2K, l 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.