Structure Magnetism And Doping Of Double Perovskite La₂CuIrO₆

Transition metal oxides?TMO?are usually electron-related systems with many functional properties.Among them,the ferromagnetic insulators have been the focus of research because of their wide application in microwave devices,permanent magnets,spin-electronic devices.The insulating TMO usually behaves as antiferromagnetic?AFM?because of the super-exchange interaction.The ferromagnetic insulators in TMO is relatively rare because of the ferromagnetism?FM?is usually accompanied by metallicity.However,many new magnetic devices require insulating ferromagnets.Therefore,it is of great practical value and significance to find new ferromagnetic insulators.5d TMO has attracted extensive research interest in condensed matter physics because of its comparable strong spin orbital coupling?SOC?,electron correlation?U?,crystal field effects and super-exchange interactions.Although much work has been done to explore and understand Ir-oxides,the highly-localized double perovskite A₂BIr O₆ compounds have been less studied.The case of double perovskite La₂CuIrO₆ is very complex and highly controversial.Therefore,the crystal structure and magnetic properties of La₂CuIrO₆ still need to be fully studied.A series of polycrystalline samples of La_2-xTi_xCuIrO₆?x=0?0.75?0.15?0.20?0.25?0.30?are prepared by solid-phase reaction.Then the structure,magnetism of double perovskite La₂CuIrO₆are studied.Based on the comprehensive analysis of X-ray diffraction?XRD?,Raman spectra and phonon spectrum,a new structural phase of P2₁/n space group is found.The magnetization of the new phase shows FM phase transition at T_C=62 K and short range FM order in the higher temperature range.The observed FM state is confirmed by DFT calculation,which indicates that the La₂CuIrO₆ sample is a Mott-insulated ferromagnet assisted by SOC.On the other hand,the doping of Ti caused the significant change of the temperature of the magnetic transition.Doping Ti ions at La-site leads to a linear decrease in the order of B-site cations with the doping concentration x,and thus the decrease of T_C.Magnetic tests show that all samples undergo ferromagnetic phase transition near Curie temperature?T_C?.The results of XPS experiments show that the charge ratio of+4 valence states in Ir ions is changed by doping Ti ions.It also changed the magnetic properties of the compounds accordingly.