Engineering magnetic anisotropy and the surface of epitaxial Fe films using ion beam erosion; unveiling self-assembly and tunability

The engineering of surface morphology and structure of the thin film is one of the essential technological assets for regulating the physical properties and functionalities of thin film-based devices. This study investigates the evolution of surface structure and magnetic anisotropy in epitaxially grown ultrathin Fe films on MgO (001) substrates subjected to multiple cycles of ion beam erosion (IBE) after growth. Ultrathin Fe film grows in 3D island mode and exhibits intrinsic fourfold magnetic anisotropy. After a few cycles of IBE, the film displays an induced uniaxial magnetic anisotropy that leads to a split in the hysteresis loop. In addition, clear and conclusive evidence of IBE mediated (2x2) reconstruction of the Fe surface has been observed. We also demonstrate that thermal annealing can reversibly tune the induced UMA and surface reconstruction. The feasibility of the IBE technique by properly selecting ion beam parameters for modification of surface structure has been highlighted apart from conventional methods of tailoring the morphology for tuning of UMA. Thus, the present work paves a way to explore the IBE-induced self-assembling phenomena further.