Multiferroic And Resistive Switching Properties Research Of Bi_0.89Ho_0.08Sr_0.03Fe_0.97-xMn_0.03Ni_xO₃ Superlatticethin Films

BiFeO₃?BFO?films,as a kind of materials with antiferromagnetism,ferroelectric and resistive switching effect at room temperature,have broad application prospects in new nonvolatile memory devices.However,in order to meet the practical application requirements of BFO films,its electrical properties need to be improved.Doping is an effective method to improve the ferroelectric properties of BFO films.Composite with magnetic films and preparation of superlattice thin films can effectively improve the interfacial effect,optimize the multiferrous properties and improve the resistive switching properties of films.In this work,Bi_0.89Ho_0.08Sr_0.03Fe_0.97-xMn_0.03Ni_xO₃?BHSFMNi_xO?thin films?Bi_0.89Ho_0.08Sr_0.03Fe_0.95Mn_0.03Ni_0.02O₃/La_0.7Sr_0.3MnO₃?BHSFMNiO/LSMO?films?Bi_0.89Ho_0.08Sr_0.03Fe_0.97-xMn_0.03Ni_xO₃?Ni_a/Ni_b?superlatticefilmsand Bi_0.89Ho_0.08Sr_0.03Fe_0.97-xMn_0.03Ni_xOsuperlattice/La_0.7Sr_0.3MnO₃?Ni_a/Ni_b/LSMO?films were prepared by sol-gel method.The effects of multielement co-doping,interfacial effect and composites on the crystal structure,morphology,ferroelectric properties,ferromagnetic properties and resistive switching properties were studied.The main results are as follows:?1?The structure,morphology,multiferroic properties and resistive switching properties of BHSFMNi_xO thin films were studied.The structure of BHSFMNi_xO thin film belongs to the rhombohedral perovskite structure,and show the state of two-phase coexistence,which has both R3m:R and R3c:H space groups.The structure of the thin films is close to the morphotropic phase boundary.The BHSFMNi_xO thin films exhibited an Ohmic or a space-charge-limited conduction?SCLC?mechanism in a low electric field,and the interface-limited Fowler–Nordheim?F–N?tunneling or the trap-assisted F–N tunneling in a high electric field.Trap-assisted F-N tunneling makes the leakage current increased,resulting in fake polarizations in the films.The interface-limited F-N tunneling effects contribute to the ferroelectric properties of BHSFMNi_xO films and make the resistive switching effect more obvious.The remanent polarization P_r of BHSFMNi_0.02O films is 193?C/cm²,the coercive field E_c is 353 kV/cm,and the saturation magnetization M_s is 5.78 emu/cm³.?2?The structure,multiferroic properties and resistive switching properties of BHSFMNiO/LSMO films were studied.Influenced by the LSMO film at the bottom,the BHSFMNiO upper layers have?110?preferred orientation.The leakage current in the film is large due to the introduction of some defects in the interface,which makes the ferroelectric hysteresis loop deformed.The remanent polarization and coercive field of BHSFMNiO/LSMO films are 33.3?C/cm² and174 kV/cm.The saturation magnetization of BHSFMNiO/LSMO films is 50.45emu/cm³,and shows superparamagnetic properties.?3?The structure,morphology,ferroelectric properties,ferromagnetic properties and resistive switching properties of Ni_a/Ni_b superlattice films were studied.The Ni_a/Ni_b superlattice thin films have excellent ferroelectric properties and good resistance switching behavior due to the interface effect caused by the tensile stress and the tiny compressive stress at the vertical interfaces,which results in the capture and release of interface charges and alleviates pinning effect.The decrease of the thickness of the single layer of the superlattice film is beneficial to the improvement of the resistive switching properties.?4?The structure,multiferroic properties and resistive switching properties of Ni_a/Ni_b/LSMO films were studied.The lattice mismatch at the interface is small due to the same perovskite structure of the Ni_a/Ni_b and LSMO films,and the ferroelectric domains in the films are more easily to reverse.The excellent magnetic properties of LSMO films are beneficial to the regulation of the magnetic properties of the composite films.Ni_a/Ni_b/LSMO films show good ferroelectric properties and diode rectifying properties.The remanent polarization and coercive field of Ni_0.02/0.03/LSMO films are 78.8?-91.7??C/cm²and 208?-178?kV/cm.The saturation magnetization of Ni_0.01/0.04/LSMO films is58.62 emu/cm³,and the films exhibit superparamagnetic properties.