Pulsed Laser Deposition And Tb Doping Of BiFeO₃Ferroelectromagnet Thin Films On Pt Substrates

Bismuth ferrite (BiFeO3) is the only one multiferroic material, in which ferroelectricity and antiferromagnetism coexist at room temperature. It offers a whole range of applications, including magnetoelectric coupling devices, sensors, spintronics, information storage memories, capacitance-inductance integration and so on. According to few studies of BiFeO3thin film prepared on Pt substrates and the bad multiferroic property, BiFeO3ferroelectromagnet thin films were prepared on Pt(111)/Ti/SiO2/Si substrates by pulsed laser deposition in the present study. The effects of deposition parameters (laser energy density, substrate temperature, oxygen partial pressure) on film crystal structure, surface morphology and ferroelectric property of BiFeO3thin films were investigated. And on this basis, the ferromagnetic property of BiFeO3films was improved by doping Tb.Firstly, the phase composition and crystallization orientation of BiFeO3thin films were controlled by adjusting the laser energy density and substrate temperature, studying the combined effects on the growth of films. The results showed that when elevating the laser energy density, single-phased BiFeO3films would be attained at higher substrate temperature. Namely, the pure BiFeO3with rhombohedral structure were obtained at1J/cm2-893K、2J/cm2-943K and3J/cm2-963K, respectively. In addition, Higher energy density and substrate temperature were favor of increasing the (111) orientation degree and dense surface morphology.Secondly, the effects of oxygen partial pressure (PO2) and substrate temperature (Tsub) on the phase, crystal structure and properties were studied, respectively. The BiFeO3films were in tetragonal or orthorhombic structure at low oxygen partial pressure, however, the structure of films was changed into rhombohedral at high oxygen partial pressure. And the quantity of Fe2+decreased with improving the oxygen partial pressure. At the appropriate oxygen partial pressure (PO2=10Pa), the film exhibited good ferroelectric property, the remanent polarization was34μC/cm2. With elevating the substrate temperature, the grain size of films increased and the integration between grains was closer. The film prepared at893K has relatively high (111) orientation degree and excellent ferroelectric property, a maximum polarization value of108μC/cm2was obtained.Finally, BiFeO3thin films were doped by Tb, and the effects of Tb content on phase, structure, and ferromagnetic property of films were researched. After Tb doping, all the Bi1-xTbxFeO3thin films were single-phased BiFeO3. The lattice constant decreased and the structural transition from tetragonal or orthorhombic to rhombohedral of occurred. With the increasing of Tb doping content, the polarization value of Bi1-xTbxFeO3thin films decreased, however, the ferromagnetic property became better. The film doped at the content of x=0.1exhibited obvious magnetic hysteresis loop, possessing a large polarization value of53μC/cm2, simultaneously. Tb doping realized the coexistence of ferroelectric and ferromagnetic property at room temperature.