Activation volume of α-Fe particles in alumite films

Abstract

The time-dependent properties of arrays of elongated and mutually aligned iron particles in alumite (anodized aluminum oxide film) have been studied. At a constant particle diameter of 11 nm, the magnetic viscosity is nearly independent of the particle length (varied from 140 to 440 nm). The activation volume (1.1 to 1.2×10−18 cm3) is almost independent of the particle length and fields: this nearly constant value is much smaller than previously reported values, but very close to the theoretical superparamagnetic limit 1.0×10−18 cm3 at room temperature.