Curie temperature of PdFe films

Ferromagnetic ordering of giant moments formed by dilute Fe in Pd host bulk alloys has been the subject of many investigations, but thin films have had little attention. Thin films exhibit evidence of a spin glass phase not observed in the bulk and a crossover from three_dimensional to two_ dimensional ferromagnetic ordering. The range of ferromagnetic ordering for PdFe is long compared to that of pure Fe, so that the crossover to two_dimensional behavior should occur in relatively thick films. A study of the effect in pure Fe would require uniform films of a few tens of angstroms. The crossover is manifested by a depression of the Curie temperature, which is expected to vary as a critical exponent of the thickness. Using a mutual inductance technique with SQUID detection, the temperature dependences of the spontaneous magnetization and the acsusceptibility were measured for some sputtered films with approximately 8% Fe. As expected, the Curie temperature decreased as the film thickness decreased. Unlike Fe, the Curie temperature of PdFe is dependent upon microstructure, and the microstructure of a film may have a systematic thickness variation that could result in a false crossover effect. The extent to which a model sensitive shift exponent can be extracted from the results is discussed.