Effect of small perturbations on the structure of domain walls in easy-plane magnets

The effect of small perturbations on the structure of 180 degrees domain walls in easy-plane magnets is studied. A scheme of the perturbation theory that permits one to calculate the configuration of a 180 degrees domain wall in the presence of arbitrary perturbations is constructed. Two types of perturbations are considered as examples: an anisotropy nonuniformity along a domain wall and a nonuniform external magnetic field. It is shown that, in the first order of the perturbation theory, weak anisotropy nonuniformities lead to changes in the structure of domain walls whose magnitude is directly related to the width and amplitude of the nonuniformity. A nonuniform magnetic field leads to a change in the shape of the domain wall, which is determined by the function that specifies the change of the field in space. A quantitative calculation of the degree of "bending" of the domain wall in a magnetic field is performed.