Source : WordNet®

demagnetise
     v 1: erase (a magnetic storage device) [syn: {demagnetize}]
     2: make nonmagnetic; take away the magnetic properties (of);
        "demagnetize the iron shavings"; "they degaussed the ship"
        [syn: {demagnetize}, {degauss}] [ant: {magnetize}, {magnetize}]