Magnetization behavior of nanometer-scale iron particles

The magnetic properties (magnetic moment, shape anisotropy, switching field, and distribution) of nanometer-scale ferromagnetic iron particles are investigated by measuring magnetization curves for different particle orientations. The measured switching fields indicate that magnetization curling accounts for the reversal at ``zero'' temperatures and an exchange length, λₑₓ=2.6 nm, is deduced. A phenomenological model describing the temperature dependence of the switching field is used to estimate the activation volume, vA=270 nm³. This is small compared to the particle volume and may explain the experimental fact that the magnetization reversal cannot be described by thermal activation over an average single energy barrier.