Physicists Devise Perfect Magnetic Shield - ScienceNOW: The superconducting shield pushes the magnetic field lines outward, creating a hole in the field. So the trick to making a cloak for static magnetic fields is to counteract that distortion... such a cloak could be made of a material that repels magnetic fields in one direction and attracts them in the opposite direction. Unfortunately, this self-contradicting material doesn't exist.
But Alvaro Sanchez of the Autonomous University of Barcelona in Spain and colleagues propose a way to approximate the impossible stuff by wrapping the cylindrical shell of superconductor in layers of materials that do one job at a time. Some layers are easily magnetized and will essentially pull the external magnetic field lines around the cylinder; those layers alternate with shells of superconducting plates that push on the field, preventing it from coming straight in toward the center. The attracting layer would be made of tiny magnetic particles, like submicroscopic iron filings, mixed into a nonmagnetic material such as plastic.