Study On The Magnetic And Electrical Properties Of Perovskite Oxides

Perovskite-type transition metal oxides have rich physical phenomena,including high-temperature superconductivity,giant magnetoresistance effects,and metal-insulator transition,which can be applied in many fields,such as sensors and magnetic memories.Among transition metal oxides,the ones including the eighth main group elements are worthy of our study because of the spin-orbit coupling effect.In this dissertation,we briefly explained the magnetoelectric properties of perovskite-type transition metal oxides containing 4d-5d elements by combined experimental explorations and theoretical investigations.In terms of theory by using the density functional theory calculation method,we compared the electronic and magnetic properties of the two series of ordered double-perovskite.One is Ba₂BOsO₆（B=Sc,Y,and In）,and the other is A₂ScOsO₆（A=Ba,Sr,and Ca）.We found the guiding principles were achieved to reveal how the electronic configurations of the bridged non-magnetic B ions and the geometric tilting of octahedra caused by small A ions dictate the strength of the magnetic interactions and the Néel temperatures.One is that the intensity of the magnetic coupling is inversely proportional to the absolute value of the energy difference between the nd orbit of Os-t_2g and the non-magnetic B cation.The other one is that the buckling of octahedral connections decreases the hybridization between Os t_2g and O 2p orbitals and the magnitude of overall magnetic exchange couplings,and abates the Néel temperatures as well.Our results not only help to better understand the inherent magnetic properties of the A₂BB’O₆ system containing only magnetic ions B’with a 5d³ electronic configuration,but also highlight the effective role of the electronic structure of non-magnetic B ions and structural distortion triggered by small A ions when adjusting the magnetic coupling strength.Last,We prepared 5SrIrO₃/nSrRuO₃（n=1,2,3,4,5,6,10 u.c.）and 20Sr IrO₃/nSrRuO₃（n=1,2,3,4,5,6,10 u.c.）and a series of heterostructures by Pulsed laser deposition,and its morphology,electronic structure and low-temperature electrical transport were tested.Initially,we have prepared atom-sized films.We tested the electronic structure of the sample and the resistance of the sample and the change of the Hall resistance with temperature and magnetic field.The experimental results show that by inserting the Sr IrO₃ buffer layer,all ultra-thin SrRuO₃ layers（less than 3 u.c.）are transformed from an insulating state to a metallic state.By metallizing ultra-thin SrRuO₃,we measure the abnormal Hall effect（AHE）for the first time in ultra-thin SrRuO₃（2 u.c.）,and the sign of the abnormal Hall conductance does not change with the temperature.Furthermore,by comparing the abnormal Hall conductance of 20SIO/n SRO and 5SIO/nSRO,we found that the sign of the abnormal Hall conductance changed in 20SIO/nSRO,and the topological Hall effect was observed in20SIO/nSRO.It is particularly interesting that in 20SIO/6SRO,the sign of anomalous Hall conductance does not change with temperature,and the topological Hall effect is still observed,which proves that the THE may be derived from sigminons instead of the opposite AHE superposition caused by uneven thickness.Observation results may reveal the existence of magnetic Skyrmions in SrRuO₃ ultra-thin films.