  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.
