Mode-crystallography analysis and magnetic structures of SrLnFeRuO6 (Ln = La, Pr, Nd) disordered perovskites.

Abstract

The crystal and magnetic structures of SrLnFeRuO(6) (Ln = La, Pr, Nd) double perovskites have been investigated. All compounds crystallize with an orthorhombic Pbnm structure at room temperature. These materials show complete chemical disorder of Fe and Ru cations for all compounds. The distortion of the structure, relative to the ideal cubic perovskite, has been decomposed into distortion modes. It has been found that the primary modes of the distortion are octahedral tilting modes: R(4)(+) and M(3)(+). The crystal structure of SrPrFeRuO(6) has been studied from room temperature up to 1200 K by neutron powder diffraction. There is a structural phase transition from orthorhombic (space group Pbnm) to trigonal (space group R3c) at T = 1075 K. According to group theory no second-order transition is possible between these symmetries. Magnetic ordering for all the compounds is described by the magnetic propagation vector (0,0,0). SrPrFeRuO(6) shows ferrimagnetic order below ca 475 K, while SrLaFeRuO(6) (below ca 450 K) and SrNdFeRuO(6) (below ca 430 K) exhibit canted-antiferromagnetic order. The magnetic moments at low temperatures are m(Fe/Ru) = 1.88 (3)μ(B) for SrLaFeRuO(6) (2 K), m(Pr) = 0.46 (4)μ(B) and m(Fe/Ru) = 2.24μ(B) for SrPrFeRuO(6) (2 K), and m(Fe/Ru) = 1.92μ(B) for SrNdFeRuO(6) (10 K).