Effect of divalent Ca ions substitution on structure and properties in multiferroic YbCrO3 chromites

The ytterbium orthochromate YbCrO₃ has a strong anisotropic exchange interaction between Cr³⁺ and Yb³⁺ ions which makes the compound exhibits negative magnetization when magnetization-temperature curves are measured in a field-cooled mode with low applied field (100 Oe). YbCrO₃ is a canted antiferromagnet (CAFM) below Néel temperature T_N=118 K. To investigate the interaction between Cr³⁺ and Yb³⁺, we chose divalent Ca²⁺ substitute for Yb³⁺ in YbCrO₃. Polycrystalline samples Yb_1-xCa_xCrO₃ with x=0.0-0.30 were successfully prepared using standard solid-state reaction. X-ray diffraction patterns show that all the samples are in pure phase which can be indexed in orthorhombic structure belonging to space group Pbnm. DC magnetization measurements show that all compounds exhibit an antiferromagnetic transition at Neel temperature. However we can not find any significant dependencies between Néel temperature and Ca concentration x. We noted that Ca substitution have a great effect on the magnitude of magnetization (M). Below the temperature where M get to maximum magnitude (T_max, e.g. about 75 K for YbCrO₃) all compounds except YbCrO₃ showed magnetic hysteresis, indicating Ca substitution brings in ferromagnetism.