Magnetization reversal in micron-size negative dot arrays in permalloy film

The magnetization reversal in two arrays of micron-size square holes in a permalloy film has been studied by means of quantitative magneto-optic Kerr vector-magnetometry. In one array, the holes form a rectangular lattice while in the other they form an oblique square lattice. In both cases, the data show that the hole arrays induce an anisotropy completely different from the original one of the non-patterned film, with hard axes along the directions connecting the holes. Also, the coercive field is strongly affected by the pattern. The results of the vector magnetometry analysis indicate that the reversal process is mainly accomplished by coherent rotation in both samples. The degree of coherency is higher (i.e. domains formation occurs later) for the sample with larger spacing between the negative dots. The domain structure in the remanent state has been investigated by magnetic force microscopy imaging.