Magnetic And Electrical Transport Properties Of Double Perovskite With A-site Substitution

The properties of double perovskite oxides with general formular A₂BB'O₆ are closely related to the B-site elements.In order to investigate the correlation between the complex magnetic behavior and B-site ions,La³⁺and Sr²⁺ions are used as substitution for A-site element which can induce the changes of valence and spin states of B-site elements.Doped double perovskite samples(La_2-xSr_xNi RuO₆ and Sr_2-xLa_xCo NbO₆)are analyzed in three aspects including crystal structure,magnetism and electrical property.The obtained main results are shown as followed.1.The magnetic and electrical properties of La_2-xSr_xNi RuO₆.La_2-xSr_xNi RuO₆(0?x?1)samples with high crystallinity and purity were successfully synthesized by the traditional solid-reaction sintering method.XRD results show that the structures of the samples with different doping ratios are monocline(P2₁/n).All the samples exhibit a weak antiferromagnetic behavior.The doping of Sr²⁺leads to the competition between ferromagnetic super-exchange and antiferromagnetic super-exchange in the samples.The dominate antiferromagnetic(AFM)interaction with weak ferromagnetic(FM)interaction was observed.The negative temperature coefficient of resistivity indicates the semiconducting nature,which fits the Variable-Range-Hopping(VRH)model.2.The magnetic and electrical properties of Sr_2-xLa_xCo NbO₆.The Sr_2-xLa Co NbO₆(0?x?1)samples with high crystallinity and purity were successfully synthesized by the traditional solid-reaction sintering method.The XRD results of Sr_2-xLa Co NbO₆ samples are refined into the cubic(Pm3m)structure.All La-doped samples show antiferromagnetic behavior.The enhancement of antiferromagnetism along with the increase of doping ratio was observed.Three different spin states of Co³⁺and low-spin state of Co²⁺result in the competition between strong AFM interaction and a weak FM interaction in the Sr_2-xLa_xCo NbO₆ samples.The resistivity of the samples exhibits a typical electrical behavior of semiconductor which is highly consistent with VRH model.