Temperature dependence of magnetic viscosity and irreversible susceptibility for aligned Stoner-Wohlfarth particle

The temperature dependence of the magnetic viscosity S and the irreversible susceptibility chi(irr) has been calculated for distributions of nonintera cting, aligned Stoner-Wohlfarth particles. Significant differences are show n to exist for volume and anisotropy field distributions. For a volume dist ribution, S-max is independent of temperature and chi(irr,max) similar to T -1/2, below the superparamagnetic temperature. For an anisotropy field dist ribution S-max approximate to c(1)T(1/2) + c(2)T and chi(irr,max) approxima te to c(3) + c(4)S(max), where the c's are positive constants. Results obta ined using approximate analytical expressions that have been previously pub lished have been compared with numerical calculations. (C) 2000 American In stitute of Physics. [S0021-8979(00)44808-5].