Dynamical study of remanent magnetization in nanoparticles

For collections of noninteracting nanoparticles, we study the reduced stati c remanent magnetization, MR, produced by the removal of a saturating magne tic field. We show that. except for special cases such as easy uniaxial ani sotropy, MR depends on both the ramp-down rate of the field and the energy dissipation rate of the spin dynamics. Using the Landau-Lifshitz equation, we illustrate this result with explicit dynamical calculations Of MR for cu bic and for mixed cubic-uniaxial anisotropies. (C) 2001 Elsevier Science B. V. All rights reserved.