11/29/2004 Permanent Magnets.doc 1/3 Jim Stiles The Univ. of Kansas Dept. of EECS Permanent Magnets For most magnetic material (i.e., where 0µµ≠), we find that the magnetization vector ()rM will return to zero when a magnetization field ()mrB is removed. In other words, the magnetic dipoles will vanish, or at least return to their random state. ()0mr=B()0mr≠B()0r≠M()0r=M11/29/2004 Permanent Magnets.doc 2/3 Jim Stiles The Univ. of Kansas Dept. of EECS However, some magnetic material, called ferromagnetic material, will retain its dipole orientation, even when the magnetizing field is removed ! In this case, a permanent magnet is formed (just like the ones you stick on your fridge)! Ferromagnetic materials have numerous applications. For example, they will attract magnetic material. Q: How? A: A permanent magnet will of course produce everywhere a magnetic flux density ()rB , which we can either attribute to the magnetic dipoles with in the material, or to the equivalent magnetic current ()mrJ . ()0mr=B()0r≠M11/29/2004 Permanent Magnets.doc 3/3 Jim Stiles The Univ. of Kansas Dept. of EECS The magnetic flux density produced by the magnet will act as a magnetizing field for some other magnetic material nearby, thus creating a second magnetization current ()mrJ within the nearby material. The magnetization currents of the material and the magnet will attract! N S
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