Superconductor/ferromagnet bilayers: Influence of magnetic domain structure on vortex dynamics

We study the magnetically coupled superconductor-ferromagnet bilayers comprised of a ferromagnet with a rotatable periodic stripelike magnetic domain structure with alternating out-of-plane component of magnetization and a MoGe superconductor. We demonstrate a prominent difference in critical current density between cases when magnetic domain stripes are oriented parallel and perpendicular to the superconducting current. The bilayer exhibits pronounced commensurability features that are related to the matching periodicities of the Abrikosov vortex lattice and the magnetic stripe domains.

Figure 1

(Color online) Magnetization curve of the $2\text{−}\mu \mathrm{m}$-thick Permalloy film as a function of magnetic field applied perpendicular to the film surface. The insets show the MFM images of the same film in (a) $H=0\mathrm{mT}$, (b) $10\mathrm{mT}$, (c) $40\mathrm{mT}$, and (d) $300\mathrm{mT}$ perpendicular magnetic field at room temperature.

Figure 2

(Color online) Magnetic field dependence of the critical current density for several temperatures: 5.0, 5.4, 5.6, 5.8, and $5.9\mathrm{K}$. The filled squares represent configuration with domain walls parallel to the transport current and the open squares represent the configuration with domain walls perpendicular to the transport current. The arrows indicate points of intersection of $j_c^{\parallel }$ and $j_c^{\perp }$ at same temperatures.

Figure 3

(Color online) Relative change of critical current density from asymptote value at several temperatures in (a) current perpendicular to stripe domains and (b) current parallel to stripe domains configuration.

Figure 4

(Color online) Resistance of the bridge as a function of applied current in (a) perpendicular configuration and (b) parallel configuration. Magnetic fields from the bottom to the top are 0, 1, 3, 7, 12, 14, 16, 18, and $26\mathrm{mT}$.