57{sup left}Fe Mossbauer study of FePtN films prepared by reactive sputtering

摘要

The intermetallic FePt alloys are the focus of current research due to their huge Ku (the magnetocrystalline anisotropy constant) values [1]. There have been many efforts in improving the hard magnetic properties, reduce the ordering temperature in these materials. The concept of intergrain exchange coupling is studied theoretically in the nano-composite magnets consisting hard magnetic phases such as Nd{sub}2Fe{sub}14B and SmCo{sub}5 and soft phases such a-Fe and shown to have improved energy product values [2]. To improve the hard magnetic properties of FePt, it would be interesting to look at the possibility of intergrain exchange coupling mechanism. Fe{sub}4N and Fe{sub}16N{sub}2 are soft magnetic materials with high saturation magnetization [3] and can be introduced conveniently into FePt films by sputtering in nitrogen - argon mixture [4]. The presence of nitrogen in the sample is expected to improve the hard magnetic properties of FePt system in two ways. First, with the inter-grain exchange coupling mechanism between soft magnetic nitride and hard magnetic FePt phase. Secondly, the nitrogen is known to escape from the sample with the high temperature annealing and therefore, it is expected that when the nitrogen escapes, the vacancies are created. Thus created vacancies might play role in increasing the diffusiveness of Fe and Pt atoms. This would result in the transformation of the disordered FePt to the ordered fct L1{sub}0 FePt phase.