On Additivity of Imperfections as Means for Domain Nucleation

The theoretical nucleation field is too high to explain experimental observation of domains, even if it is assumed that in a certain region the magnetocrystalline anisotropy constant $K$ is zero. In order to see to what extent the effect of such regions can be additive, a study is reported here of the two one-dimensional cases. In the first case, the regions of $\text{K\hspace{0.17em}=\hspace{0.17em}0}$ extend periodically over the whole (infinite) material. In the second case, there are 2 such regions. The periodic case is found to yield somewhat larger nucleation field than the second case. In both cases the reduction in nucleation field with respect to the perfect material is only one order of magnitude for reasonable defect size, and is slightly less than for one defect of the same size.