PHASE-DIAGRAM AND MIXED-PHASE DYNAMICS OF THE DILUTE ISING ANTIFERROMAGNET FEXMG1-XCL2, .7-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1

Using magneto-optical techniques, i.e. Faraday rotation, imaging and ' transparent magnetic circular dichroism', we have investigated the ant iferro-paramagnetic mixed phase of FexMg1-xCl2, 0.7 < x < 1, in a long itudinal magnetic field H. The observed domain patterns are time and h istory dependent. The phase boundaries reveal a strong dynamic behavio ur at low temperatures, T similar to 0.1T(N). Spin-glass-like slow rel axation is observed above the mixed phase boundary. At dilution x = 0. 7 and T < 2 K, re-entrant spin glass phenomena are observed in fields below the lower mixed phase boundary.