The Induced Magnetic Anisotropic Variation Of Perovskite Cobalt Manganese Oxides Thin Films

Perovskite transition metal oxides have many novel physical phenomena.Among them,perovskite type cobalt and manganese oxides have been the research focus of condensed matter physics due to their wide application in spintronic devices.Lanthanum cobaltite(La Co O₃),as a typical cobalt oxide,has unique magnetism and abundant spin states,which are shown in the following aspects:the bulk does not have magnetism,but it shows obvious ferromagnetism,when it exists as a thin film and its spin order arrangement will show high spin state,medium spin state and low spin state under external action;the manganese oxide lanthanum strontium manganate(La_0.7Sr_0.3Mn O₃)has semi metallic properties,high Curie temperature and colossal magnetoresistance effect,it has broad application prospects in spin valves,magnetic tunnel junctions and other devices,therefore it has attracted extensive attention of researchers.In addition,in the oxide heterostructures,the existence of polarity discontinuities at the interface leads to the generation of novel physical phenomena such as two-dimensional electron gases and superconductivity,which makes the system of polarity discontinuities a new research hotspot.This paper focuses on typical perovskite transition metal oxide La Co O₃ and La_0.7Sr_0.3Mn O₃films as well as SrCuO₂/SrMnO₃ heterostructures,and the magnetic properties are controlled by means of stress,orientation and polarity.Its contents are listed as follows:(1)Using pulsed laser deposition equipment with reflective high-energy electron diffraction,a series of high-quality La Co O₃ films were prepared on(001)-oriented Sr Ti O₃(STO)?(La Al O₃)_0.3(Sr₂Al Ta O₆)_0.7(LSAT)?La Al O₃(LAO)?YAl O₃(YAO)substrates.Through the magnetic test,the magnetic anisotropy of the LCO films was found.And we also found ferromagnetic signals were found on both tensile and compressive substrates.The change of stress from tensile to compressive about LCO films,the easy axis will also change from the initial in-plane direction to the out-of-plane direction.At the same time,we also measured the percentage of Co²⁺in different LCO films from 12.8%to 10.6%by X-ray photoelectron spectroscopy.It is proved that this small change has a relatively weak effect on the huge different magnetization of LCO films.(2)The effects of different orientations of the same substrate and different substrates with the same orientation on the anisotropy of LSMO films were systematically studied.High quality LSMO epitaxial films with thickness of 13 u.c.(5 nm)were prepared by pulsed laser deposition with RHEED system.For(001)orientation,the films on STO and LSAT under tensile stress tends to be in-plane,while that on LAO under compressive stress tends to be out of plane.For LSMO films on(110)oriented substrates,the in-plane orbital 3z²-r² is preferentially occupied on STO and LSAT substrates which provide tensile stress,while the electronic orbital x²-y² is preferentially occupied on LAO substrates which provide compressive stress.The experimental results show that the magnetic anisotropy and orbital occupancy of LSMO films are affected by the stress and orientation.(3)Design and prepare[(SrCuO₂)_n/(SrMnO₃)₆]₁₀ superlattice samples,n=2?8.It is found that the thickness of SrMnO₃ remains unchanged,and with the decrease of the thickness of SCO layer,the atomic configuration of copper oxygen surface changes from planar structure to chain structure.With the change of the structure,the magnetic order in the out-of-plane direction of the heterostructures also changes,as the thickness of SCO increases,the saturation magnetization of the heterostructures decreases gradually.When the thickness of SCO reaches seven unit cells,the saturation magnetization of the heterostructures increases gradually.When the SCO layer is thinner in the heterostructures and presents out of plane chain structure,there is strong exchange between Cu and Mn at the interface.It will produce interface ferromagnetic order,so the saturation magnetization is stronger when the SCO layer is thinner;when the SCO layer becomes thicker and presents a planar structure,the exchange interaction between Cu and Mn at the interface is broken.At this time,the copper oxide shows the antiferromagnetism in the non-compensatory state of the bulk,and the saturation magnetization increases slightly.In conclusion,the effects about perovskite transition metal oxide films are studied on the anisotropy and magnetic properties,of which is stress,orientation and polarity discontinuity.These studies contribute to the understanding of perovskite transition metal oxides,and have a certain guiding significance for the future research.