Anomalous Behavior of the Anisotropy and Linewidth due to Pr in Iron Garnets

The contribution of Pr³⁺ in iron garnets to the first-order anisotropy constant and to the microwave loss is highly nonlinear with respect to the Pr³⁺ concentration and is shown to be strongly dependent on the lattice constant. The value of the anisotropy constant per Pr ion goes from -18×{}10⁴ to about +3×{}10⁴ erg/cm³ as the lattice constant increases from 12.4 to 12.7 {}. The microwave linewidth of Pr₃ScFe₄{O}₁₂$ is 21 times narrower than expected from the extrapolation of the low-concentration data of ${Pr}³⁺$ in yttrium iron garnet.