Switching from ferro- to antiferromagnetism in A2CrSbO6 (A = Ca, Sr) double perovskites: a neutron diffraction study

Abstract

Double perovskites Sr₂CrSbO₆ and Ca₂CrSbO₆ have been prepared by a solid-state procedure. The crystal and magnetic structures have been studied from X-ray (XRD) and neutron powder diffraction (NPD) data. Rietveld refinements show that the room-temperature crystal structure is monoclinic (space group P2₁/n), and contains an almost completely ordered array of alternating CrO₆ and SbO₆ octahedra sharing corners, tilted along the three pseudocubic axes according to the Glazer notation a⁻a⁻b⁺. The monoclinic distortion is larger in Ca₂CrSbO₆ than in Sr₂CrSbO₆, which is associated with the tilting of the CrO₆ and SbO₆ octahedra, displaying tilting angles φ = 13.5° and φ = 5.5°, respectively. Magnetization measurements and low-temperature NPD data show that Sr₂CrSbO₆ is an antiferromagnet with a Néel temperature of 12 K with an ordered magnetic moment of 1.64(4) μ_B per Cr³⁺. The propagation vector is k = 0. Ca₂CrSbO₆ exhibits ferromagnetic long-range order below T_C = 16 K, with a saturation magnetization of 2.36 μ_B at 5 K. In the ferromagnetic arrangement, the Cr³⁺ spins are aligned approximately along the [110] direction with an ordered magnetic moment of 2.6(2) μ_B. To our knowledge, this is the first example of a ferromagnetic double perovskite containing a non-magnetic element in the B positions of the perovskite structure.