Magnetic and M$\stackrel{..}{o}$ssbauer investigations of new antiferromagnetic compounds of $RFeGe_2O_7(R=La-Gd)$

Compounds $RFeGe_2O_7$ containing two kinds of magnetic ions - $Fe^{3+}$ and $R^{3+}$ (R = La-Gd) - are synthesized for the first time. The M$\stackrel{..}{o}$ssbauer spectra of $^{57}Fe^{3+}$ are measured, together with its magnetic and elastic properties; antiferromagnetic ordering at temperatures 5-9 K is observed. The ordering temperatures, paramagnetic temperatures, and superfine fields at $^{57}Fe^{3+}$ nuclei are determined. It is concluded that the $R^{3+}—Fe^{3+}$ interaction in these compounds is comparable with the $Fe^{3+}—Fe^{3+}$ interaction, and makes a significant contribution to the magnetic and elastic properties.