The reversal of spins in a magnetic material as they relax toward equilibrium is accompanied by the release of Zeeman energy which can lead to accelerated spin relaxation and the formation of a well-defined self-sustained propagating spin-reversal fr
ont known as magnetic deflagration. To date, studies of Mn$_{12}$-acetate single crystals have focused mainly on deflagration in large longitudinal magnetic fields and found a fully spin-reversed final state. We report a systematic study of the effect of transverse magnetic field on magnetic deflagration and demonstrate that in small longitudinal fields the final state consists of only partially reversed spins. Further, we measured the front speed as a function of applied magnetic field. The theory of magnetic deflagration, together with a modification that takes into account the partial spin reversal, fits the transverse field dependence of the front speed but not its dependence on longitudinal field. The most significant result of this study is the finding of a partially spin-reversed final state, which is evidence that the spins at the deflagration front are also only partially reversed.
The energy released in a magnetic material by reversing spins as they relax toward equilibrium can lead to a dynamical instability that ignites self-sustained rapid relaxation along a deflagration front that propagates at a constant subsonic speed. U
sing a trigger heat pulse and transverse and longitudinal magnetic fields, we investigate and control the crossover between thermally driven magnetic relaxation and magnetic deflagration in single crystals of Mn$_{12}$-acetate.
Very fast magnetic avalanches in (La, Pr)-based manganites are the signature of a phase transition from an insulating blocked charge-ordered (CO-AFM) state to a charge delocalized ferromagnetic (CD-FM) state. We report here the experimental observati
on that this transition does not occur neither simultaneously nor randomly in the whole sample but there is instead a spatial propagation with a velocity of the order of tens of m/s. Our results show that avalanches are originated in the inside of the sample, move to the outside and occur at values of the applied magnetic field that depend on the CD-FM fraction in the sample. Moreover, a change in the gradient of the magnetic field along the sample shifts the point where the avalanches are ignited.
