Random-Field Effects on Critical Behavior of Diluted Ising Antiferromagnets

Random-field effects have been studied, using linear birefringence, in the random Ising antiferromagnets FeₓZn_1-xF₂ and MnₓZn_1-xF₂. with 0<H₀<~20 kOe parallel to c, large shifts in Tc and dramatic changes in the shapes of the transition peaks were observed. These results confirm some, but not all, theoretical predictions and suggest an effective dimensionality d2. No H₀-induced rounding was observed. This is shown to be consistent with the rounding seen in other experiments at larger values of gμBH₀kTc.