Measurement of magnetic anisotropy constant for magneto-optical recording media: A comparison of several techniques

Experimental data of the intrinsic perpendicular magnetic anisotropy energy constant K_u are presented for amorphous rare earth-transition metal (RE-TM) Tb_x(FeCo)_1-x and multilayered Co/Pt thin film samples. These data were independently measured using five techniques based on torque magnetometry, the extraordinary Hall effect, and the magneto-optic Kerr effect. In the Hall effect measurement, the external field was applied to the sample in three different ways: fixed at 45°from the film normal; rotating around the sample; and fixed along the in-plane direction. The results obtained with these techniques agree with each other for the Co/Pt samples. However, we do find systematic differences in the measured K_u for the Tb _x(FeCo)_1-x samples. For example, K_u given by the Hall effect and Kerr effect is always larger (by up to a factor of 3) than that given by torque technique. Another interesting fact is that K_u given by the Hall effect technique drops as x approaches the compensation point x_c in the TM-dominant case, but increases as x approaches x _c in the RE-dominant case. These experimental results are explained by taking into account the canting between RE and TM subnetworks.