Resonant perturbation of spin waves in KMn0.99Mg0.01F3 and KMn0.96Zn0.04F3

The perturbation of spin waves in the perovskite antiferromagnet KMnF3 by non‐magnetic Mg and Zn impurities has been studied by neutron inelastic scattering. On the basis of Ising theory, a resonant perturbation is expected at about 1.9 THz, and a marked resonant perturbation center in the range 1.8–1.9 THz is observed for both materials. For KMn0.99Mg0.01F3, single‐peaked lineshapes are observed with a maximum impurity‐induced width Γ of 0.107±0.012 THz. For KMn0.96Zn0.04F3, double‐peaked lineshapes are observed near resonance and the maximum Γ is 0.354±0.01Pd5 THz. The effect of the impurities on the frequencies is small relative to the effect on the widths.