Ferromagnetism from Undressing
  We have recently proposed that superconductivity may be understood as driven by the undressing of quasiparticles as the superconducting state develops. Similarly we propose here that ferromagnetism in metals may be understood as driven by the undressing of quasiparticles as the ferromagnetic state develops. In ferromagnets, the undressing is proposed to occur due to the reduction in $bond$ $charge$ caused by spin polarization, in contrast to superconductors where the undressing is proposed to occur due to the reduction in $site$ $charge$ caused by (hole) pairing. The undressing process manifests itself in the one and two-particle Green's functions as a transfer of spectral weight from high to low frequencies. Hence it should have universal observable consequences in one- and two-particle spectroscopies such as photoemission and optical absorption. 
J.E. Hirsch