Electric Field Control Of Physical Properties In 'Perovskite Manganites/ferroelectric' Heterostructures

Multiferroics is a kind of multi-functional material containing two or more basic properties of iron,which possesses rich physical properties and wide application prospects.In this thesis,lanthanide-doped perovskite manganese oxides and their multiferroic composite thin films were experimentally prepared.The magnetic properties of the manganese oxides,as well as the modulation effects of electric field on magnetic properties and mechanism of the tuning effect in manganese oxides based-magnetoelectric thin film,were investigated.The main contents and results were summarized as following.First,La2/3(Ca0.6Ba0.4)1/3MnO3(1#LCBMO)bulk material and 1#LCBMO/SiO2 thin film were prepared by sol-gel method and pulsed laser deposition(PLD)method,respectively.Then,the structural,magnetic properties and magnetocaloric effect of bulk and thin films were studied.The results show that pure phase samples present ferromagnetic properties and obvious magnetocaloric effect.Under an external magnetic field of 2T,the magnetic entropy change of up to 2.1J/kg-K and 8.4mJ/cm3·K in respective Curie temperature were obtained in the bulk and thin film,respectively.Then,based on the preparation process of 1#LCBMO/SiO2 thin film,We prepared 1#LCBMO/PMN-PT(011)magnetoelectric(ME)thin film,i.e.,1#LCBMO was epitaxially grown onto PMN-PT(Oll)ferroelectric single crystal substrate by PLD method.The modulation effect of electric field on both magnetic&electric transport properties and magnetocaloric effect of the ME film were well investigated.The results show that in-situ electric field has a significant effect on the magnetization,Curie temperature and magnetic entropy change of the sample.Besides,ex-situ electric field presents tuning effect on the electric transport properties of the film,i.e.,electric field induced the change of resistance(named as electroresistance(ERE)effect.Also,the magnetoresistivity of the film is significantly changed and metal-insulator transition temperature(Tp)of the film is shifted to high temperature region.Finally,based on the idea that many physical properties occur in Cure temperature(Tc),we expect that obvious modulation effect of electric field on magnetic properties in FM/FE ME composite can be realized near room temperature.Therefore,we attempt to modulate Tc by changing the mole rate of Ca2+ and Ba2+in La2/3(Ca1-xBax)1/3MnO3 thin film systems.After several attempts,we selected La2/3(Ca0.2Ba0.8)1/3MnO3(2#LCBMO)for follow-up investigation.2#LCBMO bulk material and 2#LCBMO/PMN-PT(011)ME thin film were prepared by the processes similar to those of 1#LCBMO bulk and thin film samples,respectively.The structure and magnetic properties of bulk and thin films,especially the magnetocaloric effect and its modulation effect by electric field,were studied.The results present that the increase in Ba2+ doping ratio can increase the TC and the temperature corresponding the maximum value of magnetic entropy change.Furthermore,the sample present obvious tuning effect of electric field on magnetism and magnetic entropy change properties.Therefore,the ME thin film may possesses important potential application on then fields of magnetic storage and room-temperature magnetic refrigeration.Meanwhile,these results provide basis work for further investigating ME coupling properties in FM/FE ME systems.