The Preparation And Physical Properties Of Double Perovskite Ln₂CuRuO₆(Ln=La,Pr,Ce,Eu)

Double perovskite materials are widely used in electrical communication and other fields due to their excellent superconducting properties,ferroelectric properties,magnetism,dielectric properties,and giant magnetoresistance effects,such as electronic devices,magnetic memory elements,and solar cell components.In the past few decades,the double perovskite oxide with the general formula A₂BB'O₆ has attracted great attention from researchers in the field of condensed matter physics.This family of quaternary compounds can be synthesized with various combinations of cations at A site(rare earth or alkaline earth elements)and B/B'(3d,4d or 5d transition metals)sites,which makes their electronic and magnetic properties very rich and complex.Different transition metal ions at the B/B'sites can give rise to a vast variety of magnetic ground states within a single structural type.Typical examples are La₂Mn Ru O₆(ferromagnetic state),La₂Fe Ru O₆(a spinglass),La₂Co Ru O₆ and La₂Ni Ru O₆(antiferromagnetic behavior).Hence,it is worthwhile to discover more La₂BRu O₆systems,which may provide the possibility for developing desired magnetic functional materials for advanced technological applications.The La₂Cu Ru O₆ is a newly discovered La₂BRu O₆-based compound.It is reported to stabilize in monoclinic phase with space group P2₁/n and an ordered arrangement of Cu and Ru atoms at B/B'sites.Based on the first-principles electronic structure calculations,the La₂Cu Ru O₆ is a ferrimagnet with antiferromagnetically coupled sublattices of ferromagnetic Cu and Ru ions.For these double perovskite compounds,the intrinsic crystal structure(e.g.lattice distortion,antisite defects)plays an important role in determining their exciting physical properties.Element substitution is one of the most effective methods to tune the lattice structure and then modulate the magnetic properties.As a consequence,various element substitution studies based on La₂Cu Ru O₆ have been performed to discover intriguing magnetic properties.But compared with the substitution and doping of B/B'site,the research on the element substitution of La₂Cu Ru O₆ at A site remains at the initial stage.Therefore,an investigation on the effect of A site substitution is highly desired,which could be crucial to better understand the(Cu,Ru)-based double perovskites.In this paper,Ln₂Cu Ru O₆(A=La,Pr,Ce,Eu)samples were synthesized by solid state reaction method,and we investigated their structural and magnetic properties of Ln₂Cu Ru O₆(Ln=La,Pr).Through comprehensive analysis of X-ray diffraction(XRD),Rietveld structure refinement and phonon spectrum,we have determined that Ln₂Cu Ru O₆(A=La,Pr)is a monoclinic crystal structure with space group P2₁/n,in which the antisite defect fraction of?3%between Cu and Ru sites in Pr₂Cu Ru O₆.From the XRD diffraction spectrum of the new compound Ln₂Cu Ru O₆(Ln=Ce,Eu),it is found that they did not form the correct phase,which may be due to the small ionic radius of Ce and Eu ions.We observe a higher ferromagnetic transition temperature of Pr₂Cu Ru O₆(Tc=32 K)than that of La₂Cu Ru O₆(Tc=15 K),possibly associated with the severe deformation of the Cu-O-Ru bond angle by substituting La³⁺with smaller ionic-radius Pr³⁺ions.In addition,the anomalous phenomenon of ZFC susceptibility at low temperature suggests a degree of magnetic frustration,and can be attributable to the intrinsic antisite defect in Pr₂Cu Ru O₆.The first principle calculations confirm a ferromagnetic Cu-Ru exchange interaction in Pr₂Cu Ru O₆,which is different from the previously reported antiferromagnetic case for La₂Cu Ru O₆.