Noise subtraction in antiferromagnetically coupled magnetic recording media

We have investigated, both experimentally and theoretically, the media noise of antiferromagnetically coupled (AFC) recording media. In particular, we have studied how the lower-layer magnetic properties affect the media noise of the composite system. We find that AFC media perform well even for intrinsically noisy lower layers, such as soft-magnetic Co or CoCr layers with high intergranular exchange coupling. To understand the experimentally observed behavior, we propose a new concept of noise subtraction in AFC magnetic systems, in which the noise of the lower layer is anticorrelated to and subtracts from the noise in the upper layers and acts as a low-pass magnetic filter of the magnetization state in the upper layer.