MAGNETIC MODELLING OF GMR HYSTERESIS AND APPLICATIONS OF THE MODELLING

Martin Sablik – Luc Dupre

   In the past several years, there has been some interest in modelling hysteresis in giant magnetoresistance (GMR) as a function of magnetic field in magnetic multilayer films. The purpose of this paper is to review work published a decade ago on such modelling and on application of such modelling to the design of a GMR field sensor. The computed GMR curves qualitatively reproduce the GMR hysteresis seen experimentally. In particular, two GMR peaks are found to be symmetrically placed about H = 0, and the GMR hysteresis curve itself is found to have an inverted butterfly shape. In the model, the hysteresis derives from the hysteretic dependence of the magnetization and from an essentially quadratic dependence of the change in the magnetoresistance on the magnetization. Multilayered films were treated as having a resistivity of different layers in parallel. Discontinuous multilayer films were treated as having blocks of magnetic and nonmagnetic material in series within the discontinuous layers. In the original model, a variant of the Jiles-Atherton model was used for the hysteresis in the magnetization. In fact, other hysteresis models for the magnetization could be used, on which the magnetoresistance then depends. A particular application utilized the Schneider model for the magnetic hysteresis and computed GMR from that for the purpose of using the modelling as a guide for designing a GMR magnetic field sensor with a minimum of magnetic noise in its measurements. In that modelling, the magnetic Barkhausen noise was computed at each point in the hysteresis cycle of the magnetic field. It was found that the magnetic noise was largest near the coercive field, but in fact the GMR decreased linearly from its peaks on both sides of H = 0 to fields well away from H_c, which indicated that the GMR could follow the field linearly in a region with very minimal magnetic noise. Thus, to produce the field sensor, a bias field is to be applied.

Keywords: giant magnetoresistance hysteresis, modelling, application to magnetic noise in GMR field sensors

[full-paper]