Magneto-optical imaging of magnetic deflagration in Mn12-Acetate

For the first time, the morphology and dynamics of spin avalanches in Mn12-Acetate crystals using magneto-optical imaging has been explored. We observe an inhomogeneous relaxation of the magnetization, the spins reversing first at one edge of the crystal and a few milliseconds later at the other end. Our data fit well with the theory of magnetic deflagration, demonstrating that very slow deflagration rates can be obtained, which makes new types of experiments possible.

Spatial motion of the magnetic avalanches associated to the CO-AFM to CD-FM transition in La$_{0.225}$Pr$_{0.40}$Ca$_{0.375}$MnO$_{3}$ manganite

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 observation 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.