Annealing effect on the structure and magnetism of Co/Pt single- and bi-crystal multilayers

Both face-centered cubic (111) single- and bi-crystal [Co(3Å)/Pt(10Å)₂₃ multilayers have been successfully fabricated on sapphire (0001) and yttria-stabilized cubic zirconia (100) substrates, respectively, via molecular-beam epitaxy. All as-deposited samples displayed a perpendicular magnetic anisotropy with coercivity of around 1000 Oe. After post annealing, bi-crystal films possessed a higher coercive field and better squareness than the other. Under post annealing at 400°C, the single crystal lost its perpendicular magnetic anisotropy because of the diffusion of Pt buffer layers and the destruction of Co/Pt multilayered structures. The coercive force of bicrystal films remained unchanged after post annealing. However, a 500°C post annealing is enough to reduce the perpendicular magnetic anisotropy of bicrystal films. The rough surface and grain boundaries may play important roles on the magnetic hardness in bicrystal systems.