Regensburg 2007 – scientific programme

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MA: Fachverband Magnetismus

MA 7: Micromagnetism/Computational Magnetics

MA 7.1: Talk

Monday, March 26, 2007, 17:00–17:15, H10

Application of exchange coupled composite layers for magnetic recording — Helmut Kronmüller and •Dagmar Goll — MPI für Metallforschung, Heisenbergstr. 3, 70569 Stuttgart

High-density recording systems require magnetic bits with large magnetocrystalline anisotropy to guarantee thermal stability. However, the large magnetic fields required for magnetization reversal cannot be afforded by conventional write heads. Therefore, composite exchange coupled spring systems of soft and hard magnetic layers are used to reduce the switching field. The reversal of magnetization in this case takes place in two steps: A nucleation process in the soft layer and a depinning process for the displacement of a domain wall (dw) into the hard layer thus inducing full switching of the exchange coupled system. The nucleation and depinning fields are calculated analytically on the basis of the continuum theory of micromagnetism. It is shown that the nucleation fields decrease according to a 1/D² law with increasing thickness D of the soft layer and in general remain smaller than the depinning fields of the dws. For longitudinal recording the depinning field is that of a Bloch wall whereas for perpendicular recording we deal with a Néel wall. The Bloch wall depinning field is found to be of the order of 1/4 of the ideal nucleation field of the hard phase. The Néel wall depinning field depends on the relative values of the spontaneous polarizations of the hard and soft phase and may be larger or smaller than the depinning field of the Bloch wall.