Critical Magnetic Scattering from KMnF3

Critical magnetic scattering experiments on the simple ionic antiferromagnet KMnF₃ are described. The observed intensity distributions are compared with those calculated from the Van Hove theory for quasi‐elastic scattering using an experimentally determined resolution function. Excellent agreement is obtained with the Ornstein‐Zernike form for the radial dependence of the correlation function in the temperature range 1.002<T/T_c<1.1. The correlation range is found to increase from 12 Å at T/T_c=1.1 to 200 Å at T/T_c=1.002 and the inverse staggered susceptibility is found to follow very closely a $\frac{4}{3}$ power law dependence on T−T_c. The results are also compared with recent results on ferromagnetic metals.