LAUSR

Abstract We study a disordered antiferromagnetic system with the focus on the magnetic-field-induced spin glass behavior. To this purpose, we consider a van Hemmen type of disordered coupling among clusters of spins and nearest-neighbor antiferromagnetic exchange evaluated within a cluster mean-field approach. We obtained several phase diagrams of temperature versus external field for different disorder strengths. As a main result, we find a mixed state (cluster spin glass coexisting with antiferromagnetism) induced by the external field in a weak disorder regime. This field-induced glassiness occurs near the critical field of the disorder-free limit, in which a frustration coming from the competition between external field and antiferromagnetic interactions is manifested by a ground-state degeneracy. In this competitive scenario, even very weak levels of disorder can drive the onset of cluster glassiness. As the disorder increases, it induces a pure cluster spin-glass phase at higher temperatures and, for large enough disorder strengths, the cluster freezing appears in the absence of an external field. We propose that one of the main mechanisms contributing to the field-induced freezing is antiferromagnetic clusters, which introduce an additional degree of freedom (the cluster magnetic moment). Therefore, weakly disordered antiferromagnetic systems with clusters would be prototypes for field-induced glassiness.