Effect of impurities on the first-order phase transition of KMnF3.

Abstract

The phase transitions at the $R$ point in KMn${\mathrm{F}}_{3}$ doped with 1% and 10% of KMg${\mathrm{F}}_{3}$, with 1% of NaMn${\mathrm{F}}_{3}$, and with 1% of KCa${\mathrm{F}}_{3}$, have been studied with x-ray scattering techniques. The Mg impurities lower ${T}_{c}$ while the others raise ${T}_{c}$, 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.