RANDOM-FIELD DESTRUCTED FIRST-ORDER PHASE-TRANSITION IN FECL2-MG

Smearing of the first-order metamagnetic phase transition in FexMg1-xCl2, 0.7 less than or equal to x < 1, is observed at low temperatures, T similar to 0.2T(N), in Faraday optical measurements. Local random fields either due to dilution and an applied field or due to a quenched antiferromagnetic (AF) domain state (DS) give rise to a crossover from first- to second-order behavior at the AF-paramagnetic (PM) field-induced transition. In agreement with model calculations the AF-PM transition field H-c is considerably enhanced when starting from a DS, which is stable even against field reversal provided that \H\ <H-c.