The Growth and Crystallisation of Polycrystalline Heusler Alloy Thin Films

Iridium is arguably the scarcest element on Earth and is currently in high demand for a number of highly technical applications. In recent years Iridium has been introduced in to the read heads of hard disk drives as well as the next generation of magnetic memory. This has led to a severe increase in the production costs of these devices because of the continuing increase in the price of Iridium. In this study the Heusler alloys Ni2MnAl and Fe2VAl have been investigated as part of a wider project to find materials that are suitable for replacing the antiferromagnetic Iridium based compounds used in magnetic media. The alloys were grown and crystallised in thin film form using Argon sputtering in order to replicate the type of films used in industry. The films were found to crystallise when annealed at a range of temperatures however the degree of ordering was not sufficient for an antiferromagnetic state to be observed. Doping the alloys with transition metals lowered the crystallisation temperature of the films and growth on a seed layer was found to greatly improve the film quality. This led to the observation of ferromagnetic ordering within the samples which was not suitable for the replacement of Iridium. An experimental protocol for energy dispersive X-ray spectroscopy using a scanning electron microscope was optimised for the measurement of Heusler alloys whereupon the combination of light and heavy elements was challenging to measure accurately. This is the first time that Ni2MnAl and Fe2VAl have been produced as polycrystalline thin films with the intention of replacing a critical material used in industry.