Manipulation Of Anisotropic Magnetic And Electric Properties Of Perovskite Oxide Heterostructures

Due to the complex interplay of order parameters in perovskite type oxide materials,the response to external regulation is very sensitive resulting in many aspects of physical characteristics.Since perovskite oxides have the advantages of simple structure,stable,high temperature resistant,strong oxidation resistance and excellent performance,they are a kind of novel functional materials with broad application prospects.In order to enhance the performance of single phase perovskite oxides,many studies are concerned about the different types of super structures with perovskite-perovskite or perovskite-others at present.In these super structures,the coupling of various order parameters have provided the possibility for the artificial control and also push the condensed matter theory constantly updated.Firstly,we try to modify the magnetoelectric properties of single layer perovskite La0.67Sr0.33MnO3(LSMO)by using the anisotropic stress and further discuss the source of anisotropy.Secondly,we try to demonstrate the strain relaxation process in the case of large stress and explore the growth mechanism of cracks in perovskite oxide film.We predicted the possibility of ferroelastic strian coupling at perovskite structure interface in theory and take the advantage of structure coupling to control the topological defects of LSMO during growth in order to microstructurally regulation of the anisotropic magneto-electric transport behaviors in LSMO.The main research works are as follows:1.We fabricate LSMO films on orthorhombic(110)o DyScO3(DSO)substrates and anisotropic patterned cracks are introduced which propagate parallel to[1-10]?direction above critical thickness as 100 nm.The propagations of cracks through the film and into the substrate are examined by cross-sectional TEM and AFM which is believed to be caused by the underlying large anisotropic strain and relatively low stiffness of DSO substrates.The electrical conduction,as large as 6.8 nA,in the crack region is firstly found and the EDX-verified LSMO deposited into cracks may be responsible for the anomalous conducting behaviors.Based on the above and substrate fracture toughness model,the growth mechanisms of cracks have been discussed.2.(110)-oreinted LSMO thin films were prepared by controlling the surface diffusivity to deposition flux ratio.Large metal-insulator transition temperature gap(39K)and resistivity anisotropy(more than 200%)were observed in the temperature-dependent transport measurements along magnetic easy and hard axis under external fields.The firstly observed paramagnetic-metallic state in[001]direction supports the emergence of anisotropic percolation of ferromagnetic domains with short-range interactions driven by the anisotropic distribution of lattice distortions.The suppression of resistivity anisotropy by vertical field shows a magnitude-related behavior which could be used to explore the intrinsic magnetic anisotropy energy and spin polarization configurations in external fields.3.We have demonstrated an alternative route to control and engineer the inhomogeneities of LSMO via periodic domain patterns of multiferroic BiFeO3.Such a LSMO/BiFeO3 heterostrucutre exhibits an anomalous electronic anisotropy,which can be tailored via the periodic domain patterns.Along with phase-field modeling and microscopic measurements,the structural coupling and inhomogeneity modulation in LSMO/BiFeO3 heterostrucutre have been revealed.Temperature-dependent resistivity measurements of a LSMO(20 nm)/BFO(20 nm)sample perpendicular and parallel to the periodic structural walls reveal the coexistence of distinct transport states in the same material system(metallic and insulating),The onsets of photo-induced ?R/R=0 started at TMI[1-10]o=164.5 K and TMI[001]o=221.0 K,respectively,which could further confirm our anisotropic transport results.Pump-probe measurements about the temperature-dependent magnetic reordering time ?r as well as the amplitude of negative component Asp-la have further unveiled the anisotropic propagation of the ferromagnetic phase in LSMO.Our present results offer a new approach to create ordered inhomogeneities in strongly correlated electron systems,and to modulate the intriguing functionalities.