Micromagnetic analysis of a coupled thin-film self-biased magnetoresistive sensor

A theoretical micromagnetic study of the basic magnetic and performance characteristics of an unshielded dual coupled thin-film self-biased magnetoresistive sensor is presented. The usual sense current flowing in the Permalloy magnetoresistor (MR) provides a magnetizing field for a strongly coupled magnetically soft adjacent layer (SAL) whose resulting demagnetization field acts as a bias source for the MR. The analysis methods presented provide quick, accurate, and numerically well-conditioned solutions of the relevant micromagnetic equations. Results presented include the self-biasing capability of the MR-SAL sensor as a function of sensor height, the MR-SAL thickness ratio, and sense current density, as well as device performance (output amplitude, second harmonic, and phase distortion) as a function of element height and record density. Theoretical results computed via the present method are compared with experimentally measured quantities as well as results (neglecting exchange) obtained via two-dimensional boundary integral methods. A brief comparison of the SAL and permanent magnet bias techniques for the MR sensor is also included.