Time-resolved Measurements of Spontaneous Magnetic Deflagration of \boldmath $\rm {Mn_{12}tBuAc}$

Magnetic deflagration in molecular magnets has been triggered by heat pulses [1,2] and acoustic waves [3,4]. In this work we report spontaneous magnetic deflagration (i.e. deflagration that occurs without an external trigger) in the axially symmetric single molecule magnet $\rm Mn_{12} tBuAc$. Magnetic hysteresis measurements show steps due to resonant quantum tunneling (RQT) below 1K, confirming the spin-Hamiltonian parameters for this material and previous results. Deflagration speeds measured with a newly constructed higher bandwidth (2MHz) setup will be presented as a function of transverse and longitudinal fields $\rm {H_x} \otimes {H_z}$ both on and off resonance. A large increase in front velocity near RQT steps is observed in experiments with swept transverse fields and will be discussed in light of models of deflagration. \\[0pt][1] S. McHugh {\it et al.} PRB {\bf 76}, 172410 (2007); [2] P. Subedi {\it et al.}, PRL {\bf 110}, 207203 (2013). [3] A. Hern\'andez-M\'inguez {\it et al.}, PRL {\bf 95}, 217205 (2005).