Structure And Physical Properties Of Fe-based Perovskite Oxide Multiferrous Film At Room Temperature

Recently,multiferroic materials have received increasing interests due to the rich physics and the great potential applications.In the present work,the preparation,structure and properties have been investigated systematically for two types of Fe-based multiferroic materials(BiFeO3(BFO)and LuInFeO3(LIFO))and the following conclusions have been obtained.The structure and physical properties of the mixed-phase BFO thin films grown on(001)-LaAlO3(LAO)and the R-phase BFO grown on(001)-SrTiO3(STO)deposited by pulsed laser deposition have been demonstrated.Compared with pure R phase BFO,mixed phase BFO has larger ferroelectric residual polarization,piezoelectric coefficient and saturation magnetization.Different conductive mechanisms are obtained by analyzing the electrical conductivity and relaxation properties.It is found that both Ea and ?t0 of the mixed phase BFO films are about 0.5 eV lower than that of the R phase BFO films.Schematic energy band for the conducting mechanism was discussed.For BFO deposited on LAO substrate,the films with a thickness of 50 nm or below exhibited a pure T phase while T-R mixed-phase was developed above this thickness.The magnetic frustration and dielectric relaxation properties of mixed-BFO with a thickness of 80 nm have been systematically examined.Temperature dependent magnetization measurements showed an antiferromagnetic Neel temperature of 350K and a freezing temperature TF of 250 K.Instead of the complex dynamics of pinned magnetic domain walls,the spin glass mechanism is responsible for the dominant magnetic response.In addition,dielectric relaxation associated with interfacial Maxwell-Wagner polarization and a large dielectric tenability of 80%was observed.The activated energy obtained from impedance spectroscopy measurements of 0.3 eV suggesting ionic conduction and possibly hopping of oxide ions is the origin of the relaxation.The stable Lu0.5In0.5FeO3 hexagonal ferrite ceramic target was obtained by In ion replacement in LuFeO3.Orthorhombic Lu0.5In0.5FeO3 thin film was epitaxially grown on STO substrate by pulse laser deposition.Temperature dependent magnetization measurements showed an antiferromagnetic Neel temperature TN of 350 K and a spin reorientation temperature TSR of 250 K.A remnant polarization of 1.5 ?C/cm2 was observed at room temperature.The structural distortion is probably responsible for the significant change in the magnetic and polarization properties.In addition,dielectric relaxation associated with interfacial Maxwell-Wagner polarization and a large dielectric tenability about 50%was observed.Lu0.5In0.5FeO3 thin films were deposited on substrates with different symmetries and lattice constants.It was found that the LIFO films grown on SrTiO3(001)and LaAlO3(001)were orthorhombic,and grown on MgO(001)and Al2O3(001)were hexagonal.LIFO thin film on STO substrate under tensile stress and has the maximum dielectric constant and minimum loss while the thin film grown on Al2O3 substrates have a high dielectric tunability of 80%.The comprehensive study of multiferroic and impedance properties shows that the stress state and crystal phase of LIFO thin film play an important role in the physical properties.For Lu1-xInxFeO3(0.3-0.6)thin films deposited on STO(001)by pulsed laser deposition.Stable orthorhombic phase can be obtained in a composition range of x=0.3-0.4.While self-assembled nanocomposite microstructure consisting of orthorhombic and hexagonal polymorphs was obtained in the range of x=0.5-0.6.High-angle annular dark field image-scanning transmission electron microscope(HADDF-STEM)analysis shows that self-assembled tapered hexagonal(h-LIFO)nanopillars with approximately circular cross-section growing perpendicular to the substrate,embedded in the orthorhombic(o-LIFO)matrix.EDS energy spectrum analysis shows that there is no deviation of element content at the interface between the two phases.The two phases are composed of grains of different sizes,the orthorhombic phase appears in the form of circular pits,whose depth increases with the increase of thickness,and there are three different domain variants.There is a huge piezoelectric coefficient of 300 pm/V at hexagonal phase and some orthorhombic phase areas.The saturation magnetization of LIFO thin films is 10 emu/cm3,and the remanent polarization is 5?C/cm2 at room temperature.A ferroelectric-gated PbZr0.52Ti0.48O3/Nd0.3Sm0.25Sr0.45MnO3 ionic liquid(IL)electric-double-layer-transistors was established.A giant modulation in the conductivity of the NSSMO channel for 13900%was achieved when applying VG of 3 V.Large nonvolatile modulation of 430%for the resistance of the NSSMO channel can be triggered through PZT ferroelectric polarizations,when removing the IL.The interfacial Ti-O-Mn bond on orbital hybridization between PZT and NSSMO layers can be controlled by ferroelectric polarization field.