Magnetism of mixed valence (LaSr) hexaferrites

The electronic structure of LaxSr1-xFe12O19 (x = 0, 0.25, 0.5, 0.75, 1) hexaferrite is calculated using the density functional theory and generalized gradient approximation (GGA). The GGA+U method is used to improve the description of strongly correlated 3d electrons of Fe. The 'virtual crystal' approach is employed for the fractional x, its applicability is checked for x = 0.5 by comparing it with the supercell method. The electronic charges introduced by the La substitution show no significant preference for any of the iron sublattices. The magnetic moment decreases linearly with the increasing La content in agreement with the experiment.