Study of Local Magnetization during Avalanches in Single Crystals of Mn12-acetate*

The temporal and spatial evolution of the local magnetization has been measured during and following magnetic avalanches that occur in Mn$_{12}$-acetate during magnetic field sweeps at low temperatures. Single crystals of various sizes and shapes were mounted on an array of micro-Hall detectors, and signals from several Hall sensors were amplified and recorded simultaneously by a data acquisition card. The local magnetization was investigated at different temperatures above 0.3 K for length scales of the order of 10 to 50 microns. We will report the approximate position where the avalanches are triggered, and the estimated speed (or set a lower limit) for propagation of the magnetization avalanches through the crystal.