Evidence for a body-centered cubic lattice of F centers was presented. A high electron spin density produced isotropic contact shifts, in the nuclear magnetic resonance spectra of the framework nuclei, whose magnitudes were a discrete function of the local electron density. Strong exchange coupling between unpaired electrons gave rise to an antiferromagnetic phase transition at 48K; thus providing the first example of an s-electron antiferromagnet.

V.I.Srdanov, G.D.Stucky, E.Lippmaa, G.Engelhardt: Physical Review Letters, 1998, 80[11], 2449-52