CoFe2O4/BaSrTiO3复合势垒多铁隧道结的制备及隧穿特性研究

CoFe2O4/ BaSrTiO3/LaCa(Sr)MnO3 multilayer films with different strain are deposited by multitarget pulsed laser deposition, and LaCa(Sr)MnO3 layer and CoFe2O4/BaSrTiO3 composite multiferroic is served as ferromagnetic and electrode layer and barrier layer, respectively. Multiferroic tunnel junction with micrometer scale is obtained by UV photolithography. Tunneling resistance is tested by scanning probe microscopy and physical properties measurement system. Tunneling magnetoresistance effect, tunneling electroresistance effect, spin filter effect are researched in tunnel junctions with different film composition and strain. The ferroelectric properties of the ferroelectric barrier layer is tuned to investigate the variation of properties of the junction, and the effect of magnetoelectric coupling on the tunneling resistance is also researched to realize the mechanism. The project will afford experimental foundation for the room temperature multistate effect.

本项目以LaCa(Sr)MnO3为铁磁层和电极层，CoFe2O4/BaSrTiO3复合多铁薄膜为势垒，借助多靶位脉冲激光沉积系统(Pulsed Laser Deposition)制备处于不同应力状态的CoFe2O4/ BaSrTiO3/LaCa(Sr)MnO3多层膜，利用紫外光刻等技术制备微米尺度的多铁隧道结。利用扫描探针显微镜技术和物性测量系统测试隧道结的隧穿电阻。研究不同组份和应力状态隧道结的隧穿电致电阻效应、隧穿磁致电阻效应、自旋过滤效应，调节铁电势垒层铁电性能来研究隧道结性能的变化，并探讨磁电耦合效应对隧穿电阻的影响以期理解其影响机制，本项目将为实现室温多阻态隧道结提供实验基础。

本项目主要利用脉冲激光沉积系统制备多层薄膜，并研究薄膜组分、厚度等因素对薄膜性能的影响，进而研究多铁隧道结中不同物理效应之间的内在联系。利用脉冲激光沉积系统分别制备了La0.7Sr0.3MnO3和SrRuO3薄膜，研究了薄膜厚度对薄膜性能的影响；并在SrRuO3薄膜上制备了BaTiO3薄膜，在薄膜较厚时薄膜呈现出较好的铁电性能；直接在Nb掺杂的SrTiO3基片上制备了BaTiO3薄膜，优化制备条件，制备出的BaTiO3薄膜呈现良好的外延生长，薄膜生长质量良好，为隧道结的研究提供了良好条件；利用相场法对Ba1-xSrxTiO3薄膜的铁电、介电等性能进行了数值模拟计算，为实验研究提供了支撑。同时还利用sol-gel法制备了PbZr0.52Ti0.48O3铁电薄膜、NiFe2O4铁氧体薄膜、BiFeO3多铁薄膜，并对这些薄膜进行了研究。另外为了制备不同的薄膜材料，在制备靶材的过程中，也对一些巨介电和铁电陶瓷材料进行了系统研究。