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Title: Magnetic field scaling of relaxation curves in small particle systems
Author: Iglesias, Òscar
Labarta, Amílcar
Keywords: Camps magnètics
Relaxació magnètica
Spin (Física nuclear)
Materials magnètics
Magnetic relaxation
Nuclear spin
Magnetic materials
Issue Date: 2002
Publisher: American Institute of Physics
Abstract: We study the effects of the magnetic field on the relaxation of the magnetization of small monodomain noninteracting particles with random orientations and distribution of anisotropy constants. Starting from a master equation, we build up an expression for the time dependence of the magnetization which takes into account thermal activation only over barriers separating energy minima, which, in our model, can be computed exactly from analytical expressions. Numerical calculations of the relaxation curves for different distribution widths, and under different magnetic fields H and temperatures T, have been performed. We show how a T ln(t/t0) scaling of the curves, at different T and for a given H, can be carried out after proper normalization of the data to the equilibrium magnetization. The resulting master curves are shown to be closely related to what we call effective energy barrier distributions, which, in our model, can be computed exactly from analytical expressions. The concept of effective distribution serves us as a basis for finding a scaling variable to scale relaxation curves at different H and a given T, thus showing that the field dependence of energy barriers can be also extracted from relaxation measurements.
Note: Reproducció del document publicat a:
It is part of: Journal of Applied Physics, 2002, vol. 91, núm. 7, p. 4409-4419
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ISSN: 0021-8979
Appears in Collections:Articles publicats en revistes (Física de la Matèria Condensada)

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