Two-Magnon Raman Scattering in KNiF3

Raman scattering of 5145‐Å argon laser radiation by two magnons in the perovskite antiferromagnet KNiF₃ has been observed. At low temperature, the spectrum of the scattered light is in excellent agreement with a Green's function theory for a perovskite with S = 1 and nearest‐neighbor exchange constant J = (71.0±0.8) cm⁻¹. If the effects of anisotropy (obtained from far‐infrared antiferromagnetic resonance measurements) are included, the value of J is changed only slightly, decreasing ≈0.5 cm⁻¹. The line shape and position were also observed as functions of temperature. A comparison is made with similar scattering observed in ${\mathrm{RbMnF}}_3\mathrm{\hspace{0.17em}(S=}\frac{5}{2})$ and in related magnetic Ni²⁺ fluorides.