Flux-line pinning by columnar magnetic defects in a type-II superconductor

The interaction of a magnetic vortex in a type-II superconductor with a cylindrical (columnar) defect filled with a nonconducting magnetic material is investigated for the first time. Analytical expressions are obtained for the vortex pinning force at such a defect. It is shown that if the material filling the cylinder has a small magnetization, then the attractive force it exerts on a vortex is determined mainly by the interaction of the vortex with the surface of the defect. In the case of a material with a large magnetization the interaction of the magnetic field of the vortex with the magnetic moments throughout the volume of the defect becomes substantial. This can serve as a good resource for enhancing the pinning efficiency.