Highly accurate 3D field gradient computation using local post-solving

To enhance the accuracy of finite element based computations of field quant ities and their derivatives, a post-solving technique with superconvergent properties is presented. This technique uses an analytical expression for t he magnetic field potential inside a closed region. The coefficients of the analytical expression are evaluated using a FE solution as boundary condit ion. AII second derivatives of the analytical expression are calculated, le ading to values for the flux density B and its derivatives. These values ar e highly accurate, even when based upon a FE solution. As an example, the ( edge) write gradient in a notch write head is evaluated.