Crystal structure and magnetic properties of wafer-size Co nanostrip arrays self-organized on a step-bunched surface of Si(111)-5.55 × 5.55-Cu/(Cu, Cu2Si, W-O) buffers

Abstract

Structure and magnetization reversal of Co nanostrips self-organized on a Si(111)-5.55 × 5.55-Cu step-bunched surface covered by Cu, Cu2Si and W-O buffer layers are systematically investigated and characterized in details. Optimal conditions for growth of well-ordered arrays of mm-long straight nanostrips with hexagonal close-packed and face-centered cubic crystal phases are defined. We find that the Co nanostrips with epitaxial and multiepitaxial structure grows on monocrystalline buffer layers of Cu and Cu2Si, respectively. The amorphous W-O buffer promotes the growth of polycrystalline Co nanostrips. We reveal the origin and compute the magnitude of magnetic anisotropy in Co nanostrips with different crystal phases. Structure-dependent magnetization reversal modes of nanostrip arrays are determined analytically using angular dependences of the coercive force. Our analysis of distributions of the switching and interaction fields by the first-order reversal curve diagram method specifies contributions of global and local interaction fields. Micromagnetic simulations considering the magnetostatic interaction between nanostrips demonstrate the crystal structure-dependent magnetization reversal mechanisms based on propagation of domain walls, whose type (symmetric or asymmetric transverse domain wall, vortex domain wall) and velocity are determined by the magnetic parameters, interaction fields and driving magnetic fields.