Domain reversal dynamics and avalanches in a model insulating Ising ferromagnet

100 years ago, Barkhausen’s noise experiments provided evidence for discrete domains within ferromagnets and magnetization reversal occurring as a set of discrete events. By characterizing individual avalanche events, the underlying mechanisms for domain reversal can be studied. Many materials show a drag effect which appears in the statistical distribution of avalanche event shapes. In typical metallic ferromagnets, this drag is believed to be due to eddy currents induced during magnetization reversal. Whether this is only significant source of drag is an open question which we address by studying the model Ising system LiHo_0.65Y_0.35F₄, an insulating rare-earth, dipole-coupled ferromagnet with T_C of 0.98 K. The LiHo_xY_1-xF₄ family combine strong quantum fluctuations, random-field pinning, and a lack of eddy currents, extending the study of domain dynamics to an entirely new regime. We find symmetrical scaled distributions near T_C, indicative of a drag-free environment. By contrast, strong asymmetries appear for long-duration events at lower temperatures, suggesting the presence of drag without eddy currents. A thermal-driven crossover between random-field effects and a quantum-fluctuation regime suggests that the latter act as the source of this additional drag mechanism.