Optical Birefringence in Dy3Al5O12(DAG) in Fields Along [111

Abstract

In fields along [111] DAG approximates a very special Ising antiferromagnet‐‐one in which applied fields couple to the antiferromagnetic order parameter (Ha‐Ms coupling). We have measured the linear magnetic birefringence of DAG in H∥ [111] with light traveling along [110] (perpendicular to the field). The Ha‐Ms coupling allows us to produce antiferromagnetic DAG in either of the two time reversed states; A+ which is absolutely stable in positive fields, and A− which is only metastable. For these two states Δn(Ha) is remarkably different (at 1.37 K and 3 kOe Δn(A+) − Δn(A−) = 10−5). The metamagnetic transition, A+ ‐ P shows as a change in Δn of about .75×10−5. These are the first measurements of linear magnetic birefringence across the A+ ‐ A− and A ‐ P transitions. Both contrasts are substantial and make possible microscopy of the mixed phase.