外延应变和铁电极化双重调控LaMnO3/BaTiO3超晶格的磁性

Dual control of magnetism in LaMnO3/BaTiO3 superlattice by epitaxial strain and ferroelectric polarization

对钙钛矿锰氧化物的磁性进行调控在科学上具有重要意义,在自旋电子学领域更是有紧迫需求.利用外延应变和铁电极化双重调控超晶格材料的磁性不但更加接近体系的真实状态,而且能诱导出丰富的物理性质.本文采用第一性原理计算,系统地研究了外延应变和铁电极化对LaMnO3/BaTiO3超晶格磁性的鲁棒控制.通过精确调控Mn原子磁矩的大小和方向,实现了铁磁■反铁磁■亚铁磁之间的可逆转变,同时产生了强烈的磁电耦合效应.除此之外,本文在超晶格中实现了铁电极化和金属性共存.通过分析Jahn-Teller效应,氧八面体旋转、倾斜以及体系内部电子转移对磁性的影响,揭示了磁性调控的物理机制.研究结果不但对系统地了解LaMnO3体系的磁性变化具有重要意义,而且可以为设计基于钙钛矿锰氧化物的自旋电子器件提供理论指导.

The controlling of magnetism of perovskite oxides is scientifically interesting and technically important for numerous functionalities in spintronic devices and next-generation magnetic memories.The experimenally prepared superlattices often contain strain,polarization,oxygen vacancy and other factors,which can affect their magnetic properties.The magnetism of superlattice materials,controlled by using both epitaxial strain and ferroelectric polarization,is not only close to the real state of the material,but also can induce rich physical properties.In this work,we demonstrate a strong magnetoelectric coupling that appears in the LaMnO3/BaTiO3 superlattice.First-principles calculations reveal that the reversible transitions among ferromagnetism,ferrimagnetism and anti-ferromagnetism are achieved by precisely controlling the magnitude and spin-direction of the magnetic moments of the Mn ions.A maximal change can be achieved to be 100.1%of the net magnetization by switching the ferroelectric polarization,which is much higher than the previous value 93.9%.The half-metallicity is demonstrated in the MnO2 layer,and accompanied by the spin polarization of the superlattice varying from 100%to 0.In addition,we realize the coexistence of ferroelectric polarization and metallicity,i.e.“ferroelectric metal”.Neither of the strong covalent Mn—O bond and La—O bond acts as an obstacle that prevents the ferroelectric polarization from penetrating the LMO layer.The Jahn-Teller effect,the tilt and rotation of oxygen octahedron,and the charge transfer of the superlattice are systemically analyzed.The variation of strain and re-orientation of polarization lead the electrons to transfer between the eg and t2g orbitals of Mn,which determines the magnetism of our system.Our purpose-designed LMO/BTO superlattice with robust intrinsic magnetoelectric coupling is a particularly interesting model system that can provide guidance for developing the spintronics for future applications.