Synthesis And Characterization Of BiFeO₃/La_0.7Sr_0.3Mo₃ Multi-layer Film

Singal multiferroics are materials in which two or more than two primary ferroic order parameters coexist simultaneously. The multiferroics researched recently are the materials with both ferroelectric order and magnetic order structures. The coexistence of magnetism and ferroelectricity in this kind of materials supplies them magneto-electric effects. Ferroelectromagnets have great potential in the field of information storage, spin electronics, non-linear magnet-light effect and transducer with coexist simultaneously of ferroelectric, ferromagnetic and magneto-electric effects.BFO (BiFeO₃) is a perovskite typed single phase mutiferrioc whose crystal symmetry belongs to the space group R3c. It was reported as simultaneously exhibiting ferroelectric ordering with Curie temperature of 1103 K and magnetic ordering with Néel temperature of 643 K. Recently, it is hot to reaserch the ferroelectric, ferromagnetic and magneto-electric effects in multilayers which were compounded with BFO thin films and perovskite typed thin films, with ferroelectric or magnetism.In the present study, BFO thin films, LSMO thin films and BFO/LSMO multilayer have been successfully synthesized by RF magnetron sputtering. The structure,surface morphology,thichness , phase of samples and electric characters were characterized by X-ray diffraction (XRD), X-Ray Reflectometry (XRR), Atomic Force Microscopy (AFM), Scanning electronMicroscopy (SEM), Transmission electron microscope (TEM) and the system for measuring at low temperatures.The major results and conclusions in our study can be summarized as following:1. We deposited Oriented LSMO,BFO and BFO/LSMO thin films on Si(001), (110) and SrTiO₃(STO)(001), (110) by RF magnetron sputtering, and studied the influence of the sputtering conditions (such as sputtering temperature, substrate material, work press and work power). The optimized condition was found in our study for despositing LSMO thin films and BFO thin films on SrTiO₃ (001). A series of multilayer samples were prepared, which BFO,LSMO sub-layer were changed,and tatal thickness was constant. 2. Oriented BFO,LSMO and BFO/LSMO thin film were deposited on SrTiO₃(001) by RF magnetron sputtering.The LSMO and BFO/LSMO thin film of PL test present strong optical properties, TEM,HEED and AFM indicated that BFO,LSMO thin film was effected stress, surface roughness and grain size were different. X-ray measurement indicated that thin film have oritented and obtained thickness.3. The series of BFO/LSMO multilayer were like series circuit in Hysteresis loop,R-T and I-V measurement, in which the BFO layers just like the intramagnetic field and the LSMO layers just like the intraelectric field. The current-induced effect in BFO/LSMO multilayer was larger and the temperature for metal-imsultor changing was higher than that in LSMO thin films, with the the contribution from intramagnetic field in the BFO layers. The mechanism of the leakage behavior in BFO layers would transform, when the intraelectric field changed. So the temperature and voltage can affect the mechanism of the leakage behavior in BFO layers by affecting the intraelectic field in LSMO layers. In general, the leakage of BFO/LSMO multilayer was lager.4. The heat treatment and doping have significant influence on oritented BFO/LSMO multilayer, heat treatment effect on electricity peoperty and doping of BFO thin film have bigger resistence than without doping. And the same heat treatment result for the doping thin film.