Pressure-induced s-band ferromagnetism in alkali metals
  First-principles density-functional-theory calculations show that compression of alkali metals stabilizes open structures with localized interstitial electrons which may exhibit a Stoner-type instability towards ferromagnetism. We find ferromagnetic phases of the lithium-IV-type, simple cubic, and simple hexagonal structures in the heavier alkali metals, which may be described as s-band ferromagnets. We predict that the most stable phases of potassium at low temperatures and pressures around 20 GPa are ferromagnets. 
Chris J Pickard and R J Needs
cond-mat.mtrl-sci