NMR Study of Random-Field Effects in a Diluted Antiferromagnet

Abstract

NMR of 19 F with no magnetic near neighbors (F o ) in the diluted antiferromagnet Mn 0.65 Zn 0.35 F 2 was used to study “random-field” effects on the critical behavior. From the temperature dependence of (1/ T 1 ), for fields applied parallel and perpendicular to the easy (c) axis, it was found that the transition temperature T c depressed substantially with field only for H o ∥ c . The field dependence of Δ T c = T c ⊥ - T c || is in general accord with the theory for random-field effects in disordered, anisotropic antiferromagnets, Δ T c ∝ h 2/φ , where h =µ H o / k T c . The value determined for the shift exponent φ=1.38±0.2 is in reasonable agreement with the prediction φ≃1.25.