Magnetic properties of amorphous iron

Ultrasonic irradiation of iron pentacarbonyl was previously shown to result in the formation of fine (approx =30 nm) amorphous, elemental-iron particles. The magnetic properties of an aggregate of these particles were measured in the present study. The particles were found to be soft ferromagnets with a saturation magnetization of approx =173 mu g and the Curie temperature > 580K. The exchange stiffness, as manifested through the coefficient of the T exp 3/2 temperature dependence in Bloch's law, is 30% that of crystalline Fe. The low-temperature magnetization curves approach saturation as the inverse square root of applied field, which is characteristic of systems with random anisotropy fields. The results are consistent with the properties of an aggregate of amorphous Fe particles of nonspherical shape, giving rise to local shape anisotropy.