Abstrakt
Charge compensation in strontium M-type hexaferrites A(x)(3+)Sr(1-x)Fe(12)O(19) (A = La, Nd, or Pr) is studied by means of calculations of electronic structure and Fe-57 nuclear magnetic resonance (NMR) experiments. Two different states are realized in the calculations: a localized scenario as a ground state with the extra valence charge preferentially in the octahedral 2a sites and a delocalized scenario with the charge delocalized over multiple sites.
From the calculations and NMR experiments, it is deduced that the localized state Fe2+(2a) occurs at low temperatures regardless of the type of used substitution and that the distribution of ferric and ferrous ions within the 2a sublattice is static at low temperatures. The magnetocrystalline anisotropy energy of Sr and La hexaferrites is calculated and the contributions of individual Fe sublattices are evaluated.
The temperature dependence of the anisotropy for La hexaferrite is explained as a transition between localized and delocalized states causing changes in the single ion contributions of Fe in 2a and also 12k sites.