Analysis of the Ferromagnetic Transition in Melt-Spun Gadolinium Nanocrystals

Abstract

Magnetic materials are present in rewriteable disk drives, electric motors and generators, and signal transformers/receivers. To improve the performance of these and other devices, much research in magnetism continues to be done. In particular, materials that are disordered on the atomic and nanometer scales have recently been the subject of extensive research, as the arrangement of atoms and the interactions between them significantly affect a material’s magnetic properties. We have prepared a disordered pure gadolinium (Gd) system using a melt-spinning technique. This resulted in a system of Gd crystals on the order of 160 nm in size embedded in an amorphous Gd matrix. The structure was identified using X-ray analysis and transmission electron microscopy. AC susceptibility and DC magnetization measurements at various temperatures (280 -350 K) and DC bias fields (0 – 3 kOe) were performed on a sample of the nanocrystalline Gd. Using modified Arrott-Noakes plots and scaling ideas for a second-order phase transition, critical exponents and the Curie temperature (TC) for the ferromagnetic transition in the nanocrystalline Gd system were obtained. TC was found to be 289.70 K, and the critical exponents had shift away from those of bulk Gd and toward those of the Heisenberg model with short-range interactions, indicating that melt-spinning suppressed the interactions present in bulk Gd.