del Barco, E, Hernandez, JM, Sales, M, Tejada, J, Rakoto, H, Broto, JM, Chudnovsky, EM.
Phys. Rev. B 60 , 11898 -11901 (1999).

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We report experimental studies and suggest a quantitative model of spin relaxation in Mn-12 acetate in a pulsed magnetic field in the temperature range 1.9-5.0 K. When the field applied along the anisotropy axis is swept at 140 T/s through a nonmagnetized Mn-12 acetate sample, the sample's magnetization switches, within a few milliseconds, from zero to saturation at a well-defined field whose value depends on temperature but is quantized in units of 0.46 T. A quantitative explanation of the effect is given in terms of a spin-phonon avalanche combined with thermally assisted resonant spin tunneling. [S0163-1829(99)11529-7].