The relationship between structure and magnetic properties in nanostructured FePd ferromagnets

FePd L1/sub 0/ ferromagnets with ultra-fine microstructures (submicron/nanoscale) have been studied. The powders and thin films with nanoscale microstructure were produced using high energy ball milling and vacuum sputtering, respectively. These ultra-fine grained materials were characterized using TEM, SEM, and X-ray diffraction. The line broadening method was used to estimate the crystallite size and lattice strain of the ball milled powders with the aid of TEM observation. The magnetic properties of the epoxy-bonded powders, isostatically pressed pellets and the thin films were measured using a vibrating sample magnetometer (VSM). The enhanced coercivities exhibited by these ferromagnets compared to bulk materials are discussed in terms of the mechanism of magnetization reversal operating in these fine-particle aggregates and thin films in the grain size range of D<Dc but well above the superparamagnetic regime. Micromagnetic analysis is applied to discuss the mechanism of coercivity, and a "pinning" model is proposed in these so-called "interaction" domain ferromagnets.