Properties of clinopyroxene LiFeGe$_2$O$_6$

The polycrystalline compound LiFeGe$_2$O$_6$ has been synthesized by the solid-phase reaction. The X-ray diffraction, Mössbauer, calorimetric, and magnetic investigations have been carried out. The Mössbauer spectrum at 300 K represents a single quadrupole doublet. The isomer shift with respect to the metal iron $\alpha$-Fe is 0.40 mm/s, which is characteristic of the Fe$^{3+}$ high-spin ion in the octahedral coordination. The quadrupole splitting of 0.42 mm/s indicates a distortion of the oxygen octahedron around the iron cation. The results of the measurement of the temperature dependence of the heat capacity in the range 2–300 K have shown the presence of the only anomaly with a maximum at $T_m\sim$ 20.5 K, which indicates the occurrence of a magnetic phase transition in this point. The data of the measurement of the temperature dependence of the magnetization have confirmed that the magnetic order with the dominant antiferromagnetic interaction of magnetically active ions exists in LiFeGe$_2$O$_6$ at a temperature below 20.5 K. The investigation of the temperature dependence of the heat capacity in the magnetic field $H$ up to 9 T has demonstrated that the external factor insignificantly changes the order-disorder transition point (at $H$ = 9 T, there occurs a shift of $\sim$0.5 K toward the low-temperature range).