Magnetic properties of solid solutions between BiCrO3 and BiGaO3 with perovskite structures

Magnetic properties of BiCr_1−xGa_xO₃ perovskite-type solid solutions are reported, and a magnetic phase diagram is established. As-synthesized BiCrO₃ and BiCr_0.9Ga_0.1O₃ crystallize in a monoclinic (m) C2/c structure. The Néel temperature (T_N) decreases from 111 K in BiCrO₃ to 98 K in BiCr_0.9Ga_0.1O₃, and spin-reorientation transition temperature increases from 72 K in BiCrO₃ to 83 K in BiCr_0.9Ga_0.1O₃. o-BiCr_0.9Ga_0.1O₃ with a PbZrO₃-type orthorhombic structure is obtained by heating m-BiCr_0.9Ga_0.1O₃ up to 573 K in air; it shows similar magnetic properties with those of m-BiCr_0.9Ga_0.1O₃. T_N of BiCr_0.8Ga_0.2O₃ is 81 K, and T_N of BiCr_0.7Ga_0.3O₃ is 63 K. Samples with x = 0.4, 0.5, 0.6 and 0.7 crystallize in a polar R3c structure. Long-range antiferromagnetic order with weak ferromagnetism is observed below T_N = 56 K in BiCr_0.6Ga_0.4O₃, T_N = 36 K in BiCr_0.5Ga_0.5O₃ and T_N = 18 K in BiCr_0.4Ga_0.6O₃. BiCr_0.3Ga_0.7O₃ shows a paramagnetic behaviour because the Cr concentration is below the percolation threshold of 31%.