Effect of the growth-and-coalescence of epitaxial islands on the formation of continuous epitaxial L10FePt thin-film and on its perpendicular magnetic domain structure

Abstract

The present work has studied using HRTEM the growth-and-coalescence behavior of epitaxial islands and its effect on the formation of continuous epitaxial $L1_0$ FePt thin-film and on its perpendicular mag-netic domain structure. The result showed that both the disordered and ordered FePt films form as epi-taxial islands on the MgO (100) substrate. However, the disordered film grows in a chain ？like structure, whereas the ordered film ($L1_0$ FePt) forms a network-like structure, where faceted islands grow towards each other to form a network of the inter-space channels between them showing the corners typically composed of 3-channels. The in-situ TEM heating study showed that the island network structure is highly stable against coalescence, whereas the disordered islands easily go through coalescence proba-bly via cluster-mobility mechanism. The coalescence of ordered $L1_0$ FePt epitaxial islands appears to occur by zipping the laterally-grown islands and filling the resulting groove by depositing atoms. The analysis of island-interface structure using XTEM showed that dislocations are formed at the root of groove and that the groove often contains a dislocation-free volume. The VSM measurement indicated that an epitaxial island network structure exhibits a large perpendicular coercivity and that the coercivity rapidly decreases with a progress of coalescence between closely-spaced adjacent islands, which leads to the formation of a percolated structure. The reason of such a rapid variation of perpendicular coer-civity is closely associated with a transition from single- to multi- magnetic domain structure as the epi-taxial islands evolve from island network structure to percolated structure.