In a magnetic head, there is provided, in the gap, {HEAD ~ a superconducting material} that has zero permeability and prevents {TAIL ~ the passage} of the magnetic field in the gap 
prevents
In a magnetic head , there is provided , in the gap , { HEAD ~ a superconducting material } that has zero permeability and prevents { TAIL ~ the passage } of the magnetic field in the gap
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH