Residual disorder and diffusion in thin Heusler alloy films

TL;DR

This study investigates the atomic-scale disorder and diffusion effects in thin Co2FeSi Heusler alloy films grown on GaAs substrates, revealing inhomogeneities and partial long-range order that impact their structural properties.

Contribution

It provides detailed analysis of the inhomogeneous atomic order and diffusion processes in Co2FeSi films, highlighting their effects on film quality and interface stability.

Findings

Inhomogeneous distribution of L2_1 and B2 phases detected

Average long-range order of 30-60% measured in films

Lateral inhomogeneities of order distribution observed

Abstract

Co2FeSi/GaAs(110) and Co2FeSi/GaAs(111)B hybrid structures were grown by molecular-beam epitaxy and characterized by transmission electron microscopy (TEM) and X-ray diffraction. The films contained inhomogeneous distributions of ordered L2_1 and B2 phases. The average stoichiometry was controlled by lattice parameter measurements, however diffusion processes lead to inhomogeneities of the atomic concentrations and the degradation of the interface, influencing long-range order. An average long-range order of 30-60% was measured by grazing-incidence X-ray diffraction, i.e. the as-grown Co2FeSi films were highly but not fully ordered. Lateral inhomogeneities of the spatial distribution of long-range order in Co2FeSi were found using dark-field TEM images taken with superlattice reflections.