Evolution of Magnetic Domain Morphology for Co/Pt Thin Films with In-Situ Field

Thin ferromagnetic films with perpendicular magnetic anisotropy show potential for being used as ultra-high-density recording devices because they exhibit a high density of magnetic domains with out-of-plane magnetization. We have found that multilayered cobalt/platinum (Co/Pt) thin films can exhibit domain densities at remanence up to 1000 domains/100 μm² when the Co thickness is optimized [1] and even remanent densities beyond 2000 domains/100 μm² for optimized number of layers. [2]. From previous studies of these films, we understand how density and morphology of their domains at remanence respond to previously applied magnetic field [1] [3] and sample composition [2]. Now we examine these changes while applying a magnetic field in-situ during MFM imaging. We examine this behavior for various numbers of layers (N), from 9 to 20, and various Co thicknesses (X) for N=20, from 10 Å to 30 Å. In these investigations, we collect MFM images at distinct in-situ field values, up to various maximum field values. We find, in agreement with previous work [2], that maximum domain density is achieved with N=20 and X=30 Å, at a maximum applied field of ~7 kG, or ~70% of its saturation point. Under these conditions, domains form a hexagonal lattice of dot states. As N, X, and the applied field vary from this optimal point, domain density decreases as domains connect to form stripes and isotropic mazes. Most often, this loss in density happens gradually as the applied field descends from the optimal density point back to remanence.