Structure-property relations characterizing the devitrification of Ni-Zr glassy alloy thin films

TL;DR

This study explores the devitrification process of Ni-Zr glassy alloy thin films, revealing structural, magnetic, and density changes during annealing, with insights from experiments and molecular dynamics simulations.

Contribution

It provides a detailed characterization of devitrification in nanometric Ni-Zr films, combining experimental data with MD simulations to elucidate structural and magnetic transformations.

Findings

Devitrification occurs at 800°C with a 3.6% density increase.

Magnetic moments increase after annealing, linked to atomic coordination changes.

Structural relaxation involves a disorder-to-order transformation influenced by short-range order.

Abstract

The investigation of devitrification in thermally annealed nanodimensional glassy alloy thin films provides a comprehensive understanding of their thermal stability, which can be used to explore potential applications. The amorphous to crystalline polymorphous transformation of cosputtered NiZr alloy (Ni78Zr22 at%) films, with a thickness lower than the reported critical limit of devitrification, was studied through detailed structural characterization and molecular dynamics (MD) simulations. Devitrification to a nanocrystalline state (Ni7Zr2 structure) was observed at 800 degC, with an increase in density (approx 3.6%) much higher than that achieved in bulk alloys. Variation in the magnetic property of the films and the overall physical structure including morphology and composition were examined before and after annealing. MD simulations were employed to effectively elucidate not only the high densification but also the increased magnetic moment after annealing, which was correlated with the simulated change in the coordination number around Ni atoms. The structural relaxation process accompanying devitrification was described as a disorder-to-order transformation while highlighting the crucial role played by chemical short range order prevalent in glassy materials.