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, lambda(ex)=2.6 nm, is deduced. A phenomenological model describing the temperature dependence of the switching field is used to estimate the activation volume, upsilon(A) = 270 nm(3). 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.