Interdiffusion in Fe/Pt Multilayers: In-situ high-temperature synchrotron radiation reflectivity study

Thermal annealing of Fe/Pt multilayers (ML) is reported to reduce significantly the formation temperature of FePt hard magnetic thin films. The transformation mechanisms of [Fe 1.38 nm/Pt 2.24 nm]50 ML, prepared by magnetron sputtering, is investigated in the present communication by high temperature X-ray reflectivity using synchrotron radiation. Complete degradation of the ML periodic structure is observed at about 610 K. The variation with annealing temperature of the intensity of the first Bragg peak, the correlated vertical roughness, and the lateral correlation length of the ML show that the ML transform in two stages with a cross-over temperature of about 515 ± 15 K. This behavior cannot be simply explained by the change in the measured interdiffusion coefficient below and above the cross-over temperature, suggesting the formation of FePt nanograins along the interfaces.