Surface effects in ferrimagnetic TbFe rare-earth–transition-metal thin films and nanoparticles

Alterations of magnetic properties associated with a large surface-to-volume ratio are of great importance for all magnetic nanosystems. In particular, amorphous rare-earth–transition-metal thin films with a thickness of 10 nm or less demonstrate modified $M\left(T\right)$ characteristics and magnetization switching behavior in comparison with their bulk counterparts. Understanding and experimentally identifying which particular surface phenomenon is responsible for this behavior are challenges due to the variety of possible overlapping contributions and effects. In this paper, we report on a study of surface magnetism in amorphous ferrimagnetic TbFe thin films and nanoparticles with varying diameters. We demonstrate how the reduction of the average number of surface neighbors, preferential oxidation, and chemical segregation can change compensation and Curie temperatures as well as magnetic reversal characteristics of the alloy. Our results indicate that the preferential oxidation plays a leading role, whereas reduction of the average number of neighbors and chemical segregation are found to be the second most important factors.