Comment on “Determination of first and second magnetic anisotropy constants of magnetic recording media” [Appl. Phys. Lett. 77, 1689 (2000)]

rer in Recently Endoet al. proposed a new method in order estimate the first and the second orders ~K1 andK2! of magnetocrystalline anisotropy in CoCrPtTa thin film media w full in-plane easy axis. The principle of their method simple and consists of measuring the magnetization al the hard axis~see Fig. 1!. By considering the first and th second orders of magnetocrystalline anisotropy, which well justified in this alloy~CoCrPtTa! due to its hexagona close-packed~HCP! structure, the total energy density in th configuration shown in Fig. 1 can be given by: ET5(ES 1K1)sin (u)1K2 sin (u)2HMssin(u), whereEs is the shape anisotropy of the thin film and it is equal to 62pMs 2 for in-plane or perpendicular media. The angular position of Ms can be determined by minimizing the total energy dens ]ET /]u 5 cos(u)@2(Es1 K1)sin(u) 1 4K2 sin (u)2HMs# 5 0. The magnetizationM, which is accessible by the measur ment, is the projection of Ms following the field direction @M /Ms5sin(u), see Fig. 1#. By including this last formula in that of the equilibrium position of Ms , the following equation can be easily established: H/M5aM1b, wherea and