Domain Structure in a Superconducting Ferromagnet

The domain structure is inherent to all ferromagnets and the recent discovery of the superconducting ferromagnets raises the question of the modification of this domain structure by superconductivity. In the framework of the general London theory, applicable to both singlet and triplet superconductors, we demonstrate that superconductivity leads to a dramatic shrinkage of the domain width. The presence of this dense domain structure has to be taken into account for all magnetic measurements on superconducting ferromagnets, and the study of the domain structure evolution could provide important information on the mechanisms of superconductivity and magnetism interplay.

Figure 1

Geometry of the considered domain system. The domain width is $\ell$ and the thickness of the film is $2L_z$. The inset shows the field distribution near a DW.

Figure 2

Evolution of the domain width with the temperature for different values of the parameters. The standard BCS type formula has been used for the temperature dependence of $\lambda (T)$. The solid line corresponds to ${\ell }_N/\lambda (0)=0.5$ and $\lambda (0)/w=100$, the dotted line to ${\ell }_N/\lambda (0)=0.1$ and $\lambda (0)/w=100$, and the dashed line to ${\ell }_N/\lambda (0)=0.1$ and $\lambda (0)/w=200$.