Zp. Zhang et al., MAGNETIZATION DIRECTION IN THE HEISENBERG-MODEL EXHIBITING FRACTIONALBROWNIAN-MOTION, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 48(4), 1993, pp. 180002327-180002330
The temporal magnetization-direction fluctuations in the three-dimensi
onal classical ferromagnetic Heisenberg model have been generated by M
onte Carlo simulation and analyzed by the rescaled-range method to yie
ld the Hurst exponent H. A value of H congruent-to 1 has been found to
apply in the ferromagnetic phase characterizing fractional Brownian m
otion, whereas a value H congruent-to 0. 5, reflecting ordinary Browni
an motion, applies in the paramagnetic phase. A field-induced crossove
r from fractional to ordinary Brownian motion has been observed in the
ferromagnetic phase.