Antiferromagnetic Barkhausen noise induced by weak random-field disorder

This study numerically investigates magnetization reversal processes driven by an external magnetic field in three-dimensional antiferromagnetic spin models with weak random-field disorder. Considering an extremely weak disorder and low temperature, we observe a stepwise hysteresis loop and the appearance of short magnetization bursts of a characteristic triangular shape; the number of bursts increases with disorder, indicative of Barkhausen-type noise. These phenomena are attributed to the simultaneous reversal at a given external field of segments composed of spins with identical neighborhoods. A local random field orients one or more spin neighbors, resulting in small, ferromagneticlike clusters distributed throughout the system. As disorder increases, these clusters may merge to form a labyrinthine structure within the antiferromagnetic background, facilitating brief avalanche propagation. The results demonstrate that, compared with familiar random-field ferromagnets, the observed antiferromagnetic Barkhausen noise and the related avalanche sequence have a profoundly different structure, organized into peaks associated with the transition between magnetization plateaus. They exhibit prominent cyclical trends and disorder-dependent multifractal fluctuations, with the singularity spectrum quantifying the degree of disorder. The activity avalanches exhibit scale invariance resembling that recently found in experiments with disordered <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mtext>ferr</a:mtext> <a:mi>i</a:mi> <a:mtext>magnets</a:mtext> </a:math> and martensites, as well as in quantum Barkhausen noise, which are associated with active geometric regions rather than individual-spin dynamics. The observed scaling behavior is interpreted in terms of self-organized critical dynamics.