Structural Anomaly and Magnetooptical Properties of FePt/Pt Multilayer Films

Multilayer films (MLF’s) composed of FePt ordered alloy and Pt were prepared by an ion beam sputtering method. X-ray diffraction in the small-angle region indicated a structural anomaly leading to the absence of the multilayer periodicity and an increase in the interplanar spacing in the direction perpendicular to the film plane when the FePt layer thickness (dFept) was around 50 A. Near this value of dFePt, the existence of an antiferromagnetic phase was confirmed on the basis of shifts in the hysteresis loops at 4.5K after magnetic field cooling. It is therefore thought that Pt-rich FePt alloy is formed in FePt/Pt MLF’s with a dFePt of around 50 Å. The spectra of θK and ηK show significant differences when dFePt>50 A and when dFePt<50 Å. This fact suggests a change in the electronic structure of FePt/Pt MLF’s occurs around dFePt=50 Å, and is accompanied by a structural anomaly.