Magnetism in Gd-W films

Abstract

Vapor condensation techniques are useful to prepare magnetic alloys whose components have low or even negligible equilibrium mutual solubility. In this work, one of these techniques-sputtering-was used to obtain Gdx W1-x alloys whose magnetic properties were investigated as a function of the Gd atomic concentration x. Gadolinium and various Gd-based alloys are promising materials for magnetic refrigeration and this was one of the motivations for this study. The Gdx - W1-x films were sputter deposited from Gd and W targets with x ranging from 0 to 1 as determined by x-ray energy-dispersive spectroscopic analyses. X-ray diffraction patterns indicate that crystalline structures were formed at low and high Gd concentrations, while at intermediate concentrations, the films were amorphous. Magnetization measurements, performed as a function of temperature and with static and alternating applied fields, reveal a spin glasslike behavior in all the W-containing samples for temperatures below the freezing temperature Tf. For low and intermediate Gd concentrations, and for T> Tf, the films were paramagnetic, while a ferromagnetic phase was observed in the Gd-W alloy of the highest Gd content. The magnetocaloric effect was investigated from the magnetization isotherms M versus H, from which the isothermal magnetic entropy variation Δ SM as a function of T, for the removal of an applied field of 50 kOe, was determined. It was observed that the maximum value of Δ SM for each Δ SM versus T curve and the temperature at which these maxima occur, are strongly dependent on x. © 2008 American Institute of Physics.