Magnetic avalanche dynamics in a model insulating Ising magnet

The dynamics and energetics of the domain reversal process in ferromagnets has been extensively studied through the mechanism of Barkhausen noise, where individual switching events generate experimentally-detectable avalanches. As the great majority of ferromagnetic materials are metallic, such switching events are typically accompanied by induced eddy currents which act as a drag force on the magnetic avalanches. Whether eddy-current drag dominates the dynamics is an important open question. We address this question by performing Barkhausen measurements on the model Ising system LiHo_0.65Y_0.35F₄, an insulating rare-earth, dipole-coupled ferromagnet with a Curie temperature of 0.980 K. We find symmetrical scaled distributions near the Curie temperature, indicative of a drag-free environment. By contrast, strong asymmetries appear for long-duration events at lower temperatures, suggesting the presence of drag even in the absence of eddy currents.