Abstract
The magnetocrystalline anisotropy and the exchange bias in nanocrystalline FeCo with and without a post-synthesis high-temperature thermal treatment have been investigated. The synthesized products were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and dc magnetization. The XRD spectra revealed the presence of secondary phases which reduced after thermal treatment resulting in the formation of single-phase polycrystalline FeCo. The FE-SEM micrographs confirmed the formation of impurities, which disappeared after thermal treatment, along with the substantial grain growth. The uniform distribution of the elements was confirmed through EDS spectra. The temperature and the magnetic field-dependent magnetization measurements under various conditions showed that, as a consequence of thermal treatment, the saturation magnetization and the magnetocrystalline anisotropy has been enhanced along with the generation of exchange bias. The phenomena of grain growth, formation of grain boundary and the exchange interactions have been described with the help of the proposed mechanism. In brief, the post-synthesis high-temperature thermal treatment induced structural as well as microstructural variations leading to the formation of grain boundaries. These grain boundaries provided interface regions for the occurrence of exchange interactions, which enhanced the magnetocrystalline anisotropy and induced exchange bias in nanocrystalline FeCo.