Abstract
We consider the zero-temperature single-spin-flip dynamics of the random-field Ising model on a Bethe lattice in the presence of an external field h. We derive the exact self-consistent equations to determine the distribution Prob(s) of avalanche sizes s as the external field increases from −∞ to ∞. We solve these equations explicitly for a rectangular distribution of the random fields for a linear chain and the Bethe lattice of coordination number z=3, and show that in these cases, Prob(s) decreases exponentially with s for large s for all h on the hysteresis loop. We find that for z≥4 and for small disorder, the magnetization shows a first-order discontinuity for several continuous and unimodal distributions of the random fields. The avalanche distribution Prob(s) varies as s −3/2 for large s near the discontinuity.
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This would happen if P*(h) as a function of h shows a ``double s'' curve. Then there must be at least 4 values of h for which the slope of the curve is infinite. This is possible only if the equation determining P*disc (variant of Eq. (29)) is at least a quartic, hence only if z≥6. 129 Random-Field Ising Model
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Sabhapandit, S., Shukla, P. & Dhar, D. Distribution of Avalanche Sizes in the Hysteretic Response of the Random-Field Ising Model on a Bethe Lattice at Zero Temperature. Journal of Statistical Physics 98, 103–129 (2000). https://doi.org/10.1023/A:1018622805347
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DOI: https://doi.org/10.1023/A:1018622805347