Magnetization and thermal expansion of single-crystal Er and Tm

The magnetization and ac susceptibility data of single-crystal Er show the antiferromagnetic ordering of the c axis and basal plane moment components at TN∥ = 87 K and TN⊥ = 53 K, respectively. In addition, we observe anomalies at 51, 40, 34, 29, and 27 K. These anomalies correspond to the commensurate spin-slip structures observed by Gibbs et al. [Phys. Rev. B 34, 8182 (1986)] in x-ray synchrotron scattering studies. From the thermal expansion study of single-crystal Er, we find that the phase transitions at TN∥ and 51 K are second order, whereas the transitions at TN⊥, 27, and 18 K are first order. The order of these transitions are in poor agreement with earlier studies of single-crystal Er. The magnetization measurements of single-crystal Tm show anomalies at TN = 57 K, Tc = 30 K, and an anomaly at 41.5 K.