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Magnetic field scaling of relaxation curves in small particle systems

# metadata.dc.description.abstract[].value
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.

# metadata.dc.source[].value
Articles publicats en revistes (Física de la Matèria Condensada)

# metadata.dc.title[].value
Magnetic field scaling of relaxation curves in small particle systems