Switching superconductivity in superconductor/ferromagnet bilayers by multiple-domain structures

We consider the effect of a multiple magnetic domain structure in a superconductor/ferromagnet bilayer, modeled by a ferromagnetic layer with a rotating magnetic moment. The domain walls in this model are of equal size as the domains, and are of Néel type. We study the superconducting critical temperature as a function of the rotation wavelength of the magnetic moment. The critical temperature of the bilayer is found to be always enhanced by the domain structure, and exhibits an interesting reentrant behavior. We suggest that this effect can be used for a new device where superconductivity may be controlled by the domain structure of the magnetic layer.

Figure 1

(Color online) Model: the moment $\mathbf{J}$ rotates in the F layer.

Figure 2

(Color online) $T_c$ vs $d_f$ for various $Q{\xi }_s$. Here $d_s=7\mathrm{nm}$. For $d_f\approx 5\mathrm{nm}$, corresponding to the dashed line, a switching effect can be observed between $Q=0$ (single domain F) and $Q{\xi }_s>0.56$.

Figure 3

(Color online) $T_c$ vs $Q{\xi }_s$ for $d_f=5\mathrm{nm}$ and various $d_s$. The thick curve corresponds to a cut along the dashed line in Fig. 2. The onsets for $d_s<7.44\mathrm{nm}$ behave like $\sqrt{Q-Q_{\mathrm{crit}}}$.