Effect of quantum tunneling on the ignition and propagation of magnetic avalanches in Mn12 acetate

Using a wire heater to ignite magnetic avalanches in fixed magnetic field applied along the easy axis of single crystals of the molecular magnet Mn(12) acetate, we report fast local measurements of the temperature and time-resolved measurements of the local magnetization as a function of magnetic field. In addition to confirming maxima in the velocity of propagation, we find that avalanches trigger at a threshold temperature which exhibits pronounced minima at resonant magnetic fields, demonstrating that thermally assisted quantum tunneling plays an important role in the ignition as well as the propagation of magnetic avalanches in molecular magnets.