ИСТИНА

The francisite, Cu3Bi(SeO3)2O2Cl, is characterized by an unique combination of chemical elements met in this mineral only. The pristine compound, Bi-francisite, experiences long-range magnetic order at TN = 24 K adopting non-collinear antiferromagnetic structure. The rare-earth’s anisotropy may influence this complex structure leading to temperature driven spin-reorientation transition. The ytterbium counterpart of mineral francisite, Cu3Yb(SeO3)2O2Cl, is synthesized and studied in measurements of magnetization and specific heat. The polycrystalline sample of Cu3Yb(SeO3)2O2Cl (sp. gr. Pmmn) have been synthesized from CuO, CuCl2, Yb2O3 and SeO2. The compound reaches antiferromagnetic order at TN = 36.7 K and experiences first-order spin-reorientation transition to ferrimagnetic phase at TR = 8.7 K. The available data suggest that non-collinear antiferromagnetic structure of Cu3Yb(SeO3)2O2Cl at TR < T < TN transforms to collinear ferrimagnetic one at T < TR.