Tracking of the Multimodal Ordering Process in FePd Alloy

This work presents the process of phase transformation and chemical ordering in an FePd alloy thin film. The study focuses on a multilayered Fe/Pd system undergoing a postdeposition annealing process. The annealing induces morphological and structural changes in the samples, which were observed by using scanning electron microscopy, X-ray reflectivity, and conversion electron M & ouml;ssbauer spectroscopy. The microscopic structural properties were examined at various stages of annealing to track the progress of the chemical ordering and transformation. Our findings reveal that the transformation to the L1(0) phase occurs through a multiphase process with two distinct paths: first, with stoichiometric (A1-A6), and second, off-stoichiometric (L1(2)-L1 ') intermediate phases. Both paths start with cubic fcc structures that undergo tetragonal distortion and successive chemical ordering to the L1(0) phase. The observed increase in transformation effectiveness correlates well with the surface diffusion-induced dewetting phenomenon and a change in the kinetic phase growth process from a low-dimensional to a three-dimensional growth mechanism. These phenomena primarily affect the growth of the L1(0) phase, which is particularly interesting for material science, spintronics, and sensorics. The use of conversion electron M & ouml;ssbauer spectroscopy allows us to study of these effects at an atomic level not accessible by other techniques.