  Permalloy (Py:Ni81Fe19) exhibits an anisotropic magnetoresistance (AMR) which
is very often used to read magnetic signals from storage devices. Py-films of
thickness 20nm were prepared by dc-magnetron sputtering in a magnetic field
onto thermally oxidized Si-wafers and annealed ex situ at temperatures up to
1000K in order to investigate the dependence of the magnetic anisotropy and the
AMR on heat treatments. The films exhibit an uniaxial anisotropy after
preparation which changes during annealing above 520K. The AMR along the former
magnetically easy axis as well as the corresponding field sensitivity are
increased by a heat treatment around 700K reaching maxima of about 8% and a
maximum sensitivity of 1.5%/Oe, respectively. We discuss possible sources for
the change in anisotropy, i.e. strain effects, inhomogeneities, and changes of
the local atomic order.
