Effect of Impurities on the First-Order Phase Transition of KMnF3

Abstract
The phase transitions at the R point in KMnF3 doped with 1% and 10% of KMgF3, with 1% of NaMnF3, and with 1% of KCaF3, have been studied with x-ray scattering techniques. The Mg impurities lower Tc while the others raise Tc, by amounts which are roughly consistent with the differences in the atomic radii. In both cases it is found that the fluctuation-driven first-order transition becomes continuous when the concentration of impurity exceeds a critical amount.