Source : Webster's Revised Unabridged Dictionary (1913)

Demagnetize \De*mag"net*ize\, v. t.
   1. To deprive of magnetic properties. See {Magnetize}.

            If the bar be rapidly magnetized and demagnetized.
                                                  --Am. Cyc.

   2. To free from mesmeric influence; to demesmerize. --
      {De*mag`net*i*za"tion}, n. -- {De*mag"net*i`zer}, n.

Source : WordNet®

demagnetization
     n : the process of removing magnetization [syn: {demagnetisation}]