In a magnetic head, there is provided, in the gap, a superconducting material that has zero permeability and prevents the passage of the magnetic field in the gap. Various alternative embodiments are used to improve the efficiency of the head by channelling the magnetic flux outside the gap....http://www.google.com.tw/patents/US4979064?utm_source=gb-gplus-share專利 US4979064 - Magnetic recording/playback head comprising a superconducting material
