The magnetostriction and magnetic anisotropy of a FeCuNbMoSiB alloy sample have been simultaneously studied from its Mossbauer spectrum in radio frequency field. The appropriately annealed nanocrystalline alloy with a crystallinity of about 60% and the average diameter of microcrystalline grain in the range of 10-20urn is found to have optimum soft magnetic performance
i.e.its magnetostriction coefficient is descended to zero and magnetic anisotropy comes to minimum simultaneously.In contrast to this
if an amorphous sample is annealed not enough or excessively
the fine soft magnetic performance will be lost because both the above-mentioned conditions can not be realized simultaneously.