Faraday-optical study of the tri-to-bicritical crossover in anisotropic heisenberg antiferromagnets Fe1-xNixCl2, 0.18 ≤x≤ 0.67

Abstract

Abstract The magnetic phase diagrams, H-vs-T and M-vs-T, of solid solutions Fe1-x Ni x Cl2, 0.18 ≤ x ≤ 0.67, are investigated using Faraday rotation measurements. Bicritical behavior is observed for x > 0.57, whereas tricritical behavior is encountered for x < 0.57. In the low-x regime a critical end-point of an additional low-T second-order spin flop-to-paramagnetic phase boundary seems to emerge linearly with x. It coalesces with the tricritical point at x = 0.57, forming a “new multicritical point” of higher order as predicted by Galam and Aharony. This merges into the bicritical point in the high-x regime.