Phase Transitions in the Mixed Quadratic-Layer Antiferromagnets with Competing Anisotropies K2Co(x)Fe(1-x)F4

摘要

The magnetic phases of the randomly mixed two-dimensional antiferromagnet K2Co(x)Fe(1-x)F4 were explored. Ordered phases similar to those in K2FeF4 and K2CoF4 are detected for low and high x, respectively. By virtue of the competition between the orthogonal anisotropies of the Fe(2+) and Co(2+) ions, a third ordered oblique phase is found for 0.20 or = x or = 0.32, in which all moments are oriented in between the preferential axes of Fe(2+) and Co2+. The critical behavior, sublattice magnetization and magnetization of individual ions, and magnetic excitations, for compositions and temperatures covering all relevant parts of the phase diagram were studied. The magnetic structure of a system which enters the oblique phase was investigated in an external magnetic field. Strong nonequilibrium behavior related to random-field effects is observed.