Media-to-sensor demagnetization matrix and its applications in micromagnetic simulation of readback process

Summary form only given. In a micromagnetic model for shielded GMR heads, it is necessary to calculate the media magnetic field inside the GMR sensor stack. It has been shown that the magnetic field in-between the two shields from magnetic charges underneath can be expressed as a Fourier series. In this work, we extend this method to derive a so-called media-to-sensor demagnetization matrix. The media magnetic field inside the GMR sensor stack is calculated from the convolution of the media-to-sensor demagnetization matrix and the media magnetization. The media-to-sensor demagnetization matrix is given by four-fold integrals of the scalar Green´s function which can be expressed as a Fourier series. This matrix can be applied to both longitudinal and perpendicular recording. The media magnetization pattern is calculated by a media micromagnetic model. All examples here are for perpendicular recording. It can be seen that the AC background is much noisier than DC backgrounds. Also the effect of the soft underlayer on readback signal is studied by including the domain wall region of the soft underlayer in the micromagnetic simulation. It is seen that the magnetization ripple pattern in soft underlayer contributes a small part of the total signal but generates most of the noise.