MAGNETIC PHASE DIAGRAMS OF GdVO4 AND GdAs04

GdAs04 and GdV04 are Heisenberg antiferromagnets with relatively large anisotropy fields, about half of which is dipolar in origin. The ratios of the anisotropy to the exchange fields for the salts, based on the molecular field theory and using the published values of the interaction constants, indicate that both salts should have spin‐flop phases. We have measured the magnetization and its derivative of GdV04 and GdAs04 as a function of applied magnetic field for various temperatures below TN and derived their magnetic phase diagrams. GdV04 (TV = 2.50 K) is a textbook type example of a system having a spin‐flop phase with T3 = 1.37 K. The critical field for the transition from the antiferromagnetic to the spin‐flop phase is 10.5 kG and that for the transition from the spin‐flop to the ferromagnetic (or saturated paramagnetic) phase is 21.8 kG. GdAs04 (TN = 1.26 K) does not have a simple spin‐flop phase but undergoes transitions to two intermediate phases before undergoing a transition to the ferromagneti...