Magnetic Anisotropy of Perpendicular Media: Measurement and Intermediate Layer Effect

We investigated the uniaxial magnetic anisotropy of perpendicular magnetic film formed on various intermediate layers (IMLs) using torque magnetometry. We carefully analyzed the shapes of the torque curves so that we could separate the magnitudes of the quadratic (Ku1) and quartic (Ku2) anisotropy energy terms. However, it turned out that the K_u values contained inevitable errors caused by the dispersion of magnetic anisotropy when they were estimated at a finite measurement magnetic field (H_ext), and that the true K_u2 terms were close to zero among all of our samples. Then, we utilized the Hext dependence of the apparent K_u values for the analysis of magnetic anisotropy dispersion of perpendicular media. Through a systematic study on various IMLs, it was directly proven that the magnetic dispersion of the CoCrPt-SiO₂ storage layer arose not only from the addition of oxide into the storage layer but also from the crystal growth on ill-suited IMLs. We further demonstrated that a Pt-Cr/Ru-laminated IML successfully avoided magnetic dispersion, which led to excellent recording performance with less total spacing between the storage layer and the soft-magnetic underlayer