Pinning of domain walls in composite particles

Single domain, composite particles (cp's) are considered to be suitable to guarantee thermal stability and switching fields of 1-2 T. Depinning fields of Bloch and Néel walls are determined for planar phase boundaries (pb's) of cp's composed of a magnetically soft and hard phase. On the basis of micromagnetism it is shown that the depinning of Bloch walls may be reduced by a factor of 4 in comparison to the nucleation field of the hard phase. In the case of perpendicular recording the depinning field of Néel walls is influenced by dipolar stray fields which may increase or reduce the depinning fields. The case of extended pb's is treated by a discretization of the potential barrier. The depinning field is determined taking into account the modification of the domain wall due to the space-dependent magnetocrystalline anisotropy.