X-ray diffraction and Mössbauer studies of structural changes and L1 ordering kinetics during annealing of polycrystalline Fe51Pt49 thin films

Abstract

Room-temperature x-ray diffraction and Mössbauer effect techniques have been used to characterize the structural features and local atomic environments of sputtered Fe51Pt49 thin films following various isothermal treatments. Both techniques show that no significant changes occur in the chemically ordered L10 tetragonal phase after it has formed. In contrast, changes in the disordered face-centered-cubic (fcc) phase are observed prior to the transformation into the ordered tetragonal phase. Mössbauer measurements indicate the development of increasing short-range order in the disordered fcc phase with increasing annealing temperature. Asymmetries in the fcc x-ray diffraction profiles also suggest the presence of lattice distortions caused by atomic size differences commonly found in the quenched disordered fcc phase of materials that form ordered structures. Quasi-real-time kinetic measurements of the disorder→order transformation in sputtered Fe51Pt49 thin films within the temperature range 300 °C⩽T⩽400 °C have also been conducted using high-temperature x-ray diffraction techniques. Significant differences are observed between the kinetic parameters determined in this study and those of previous reports. It is proposed that these differences arise from the lower temperature range investigated in the present work, where the gradual changes occurring in the fcc phase can influence the rate of the ordering transformation. Furthermore, because the initial state of disorder in Fe∼50Pt∼50 films can be influenced by the deposition conditions, variability in the low-temperature ordering kinetics should be expected among Fe∼50Pt∼50 films prepared under different conditions.