Affiliations: [a] Magnetic Materials Research Group, Center for
Materials Science, University of Central Lancashire, Preston, PR1 2HE,
UK | [b] Department of Physics, University of Durham, Durham,
DH1 3LE, UK | [c] "Al. I. Cuza" University, Iasi, Romania | [d] Department of Physics, University of York, York, YO10
5DD, UK
Abstract: A Monte Carlo time and temperature dependent model was developed to
simulate magnetization processes in fine ferromagnetic particle media. The
model uses a combination between a time dependent Stoner-Wohlfarth model and a
standard Metropolis algorithm to find the magnetization of single-domain
particle systems. Both magnetostatic and exchange interactions are introduced
explicitly. Variation of magnetic viscosity with interactions and temperature is
studied. Results show that viscosity exhibits a maximum around coercive field.
The value of this maximum is closely related to the strength and the origin of
interactions as well as to temperature. Dipolar interactions decrease the
viscosity and broaden the viscosity vs. field curve, while exchange
interactions lead to an increase in viscosity around coercive field. An
increase in temperature up to the critical temperature for the
superparamagnetic behavior leads to an increase in viscosity. Further increase
of temperature produces a decrease in viscosity.
