Perpendicular Magnetic Properties on hcp-Co₈₀Pt₂₀ Stacked Films with Oxide Seed Layers

Abstract

The influence of oxide seed layers on the magnetic properties and crystalline structures of hcp-Co₈₀Pt₂₀ perpendicular magnetic thin films were investigated for magneto-optical chemical and biological sensing system. Cr-O, Al-doped ZnO (AZO) and Al₂O₃ films were used as the oxide seed layers. The Cr-O layer was most effective to improve the perpendicular magnetic properties of Co-Pt. The Cr-O seed layer produced the largest values of the interfacial perpendicular magnetic anisotropy (K_S) and perpendicular magnetocrystalline anisotropy (K_V). The investigation in the crystalline and chemical bonding conditions suggested that the both perpendicular magnetic anisotropies were originated from the interaction of Co and oxide at the Co-Pt/Cr-O interface. The improvements of K_S and K_V on the Cr-O seed layer are attributed to the hybridization of Co-3d and O-2p orbits and the hcp(001)-CoPt crystal growth with self-orientation, respectively. We also demonstrated the magneto-optical cavity effect on the Co-Pt perpendicular magnetic stacked films with the Cr-O intermediate layer. The stacked films indicated a large magneto-optical response by optical interference and good perpendicular magnetic properties with an ideal square shaped hysteresis loop.

Fig. 1　Magneto-optical polar Kerr loops for Co-Pt stacked films with oxide seed layers of Cr-O (red solid line), AZO (blue dashed line) and Al₂O₃ (black dotted line). The thicknesses of Co-Pt and oxide seed layers were 14.9 nm and 30 nm, respectively. The Kerr rotation angles (θ_K) were normalized by the saturation Kerr angle (θ_S) of each sample, and all hysteresis loops were measured at a wavelength of 400 nm.