Spontaneous volume magnetostriction and non-Stoner behavior of the valence band in pure hcp Gd

Employing the disordered local moment formalism in combination with first-principles band-structure calculations, we study the behavior of the valence band in pure hcp Gd upon disorder of the local $4f$ GD moments. We show that the large value of the spontaneous volume magnetostriction in Gd is entirely due to changes in the magnetic state of the valence band at Tc and can be calculated in good agreement with experiment. The local exchange splitting of the valence band persists above Tc, which is in strong disagreement with the conventional Stoner picture. The analysis of our results provides a theoretical background for the discussion of recent photoemission experiments.