Effect of temperature-dependent shape anisotropy on coercivity for aligned Stoner-Wohlfarth soft ferromagnets

Abstract

The temperature variation effect of shape anisotropy on the coercivity, H C (T), for the aligned Stoner-Wohlfarth (SW) soft ferromagnets, such as fcc Ni, fcc Co and bcc Fe, are investigated within the framework of Néel-Brown (N-B) analysis. An extended, by introducing a single dimensionless correction function, the reduced magnetization,, in which τ = T/T C is the reduced temperature, M S (T) is the saturation magnetization, and T C is the Curie temperature. The factor, m(τ), accounts for the temperature-dependent effect of the shape anisotropy. The constants, H 0 and E 0 , are for the switching field at zero temperature and the potential barrier at zero field, respectively. According to this newly derived equation, the blocking temperature 2 above which the properties of superparamagnetism show up is described by the expression, T B = E 0 m 2 (τ Β )/[k B ln(t/t 0 )], with the extra correction factor m 2 (τ Β ). The possible effect on H C (T) and the blocking temperature, T B , attributed to the downshift of T C resulting from the finite size effect has been discussed also.3

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