Structural chemistry and magnetic properties of hexagonal perovskites BaIrxMn1−xO3, x = 0.3, 0.4, 0.5

Abstract

The crystal structures and magnetic properties of BaIr_xMn_1−xO₃, x = 0.3, 0.4, 0.5, have been investigated using a combination of X-ray and neutron powder diffraction, and d.c. magnetometry. The hexagonal 9R perovskite structure (space group Rm, a ≈ 5.7 Å, c ≈ 21.4 Å), built up from corner-sharing trimers of face-sharing octahedra, is adopted across the series. High resolution neutron diffraction data confirm that the Mn⁴⁺ and Ir⁴⁺ cations exist in a disordered distribution across the two octahedral cation sites and indicate that for each composition, the oxygen content is stoichiometric. Low temperature neutron diffraction studies revealed the presence of a long-range magnetic order at 5 K consistent with an antiferromagnetic arrangement of spins. A combination of d.c. magnetometry and neutron diffraction has allowed the Néel temperature (T_N) of BaIr_0.4Mn_0.6O₃ to be identified as 100(5) K, whilst T_N for BaIr_0.3Mn_0.7O₃ is 135(5) K. The susceptibility data also provide evidence that a proportion of the spins remain decoupled from the long-range antiferromagnetically ordered state and that a transition which involves the freezing of these spins in a glassy manner occurs at T_f = 45(1) K for each sample.