Neutron Powder Diffraction Study on the Crystal and Magnetic Structures of BiCrO3

摘要

The crystal and magnetic structures of poly crystalline BiCrO3 were determined by the Rietveld method from neutron diffraction data measured at temperatures from 7 to 490 K. BiCrO3 crystallizes in the orthorhombic system above 420 K (space group Pnma; Z = 4; a = 5.54568(12) A, b = 7.7577(2) A, and c = 5.42862(12) A at 490 K) in the GdFeO3-type structure. Below 420 K down to 7 K, a monoclinic structure is stable with C2/c symmetry (a = 9.4641(4) A, b = 5.4790(2) A, c = 9.5850(4) A, and β = 108.568(3)° at 7 K). A possible model for antiferromagnetic order below T_N = 109 K is proposed with a propagation vector of k = (0, 0, 0). In this model, magnetic moments of Cr~(3+) ions are coupled antiferromagnetically in all directions, forming a G-type antiferromagnetic structure. Refined magnetic moments at 7, 50, and 80 K are 2.55(2)μ_B, 2.43(2)μ_B, and 2.09(2)μ_B, respectively. The structure refinements revealed no deviation from stoichiometry in BiCrO3.