Atomic-Scale Control of Magnetism at the Titanite-Manganite Interfaces

Abstract

Complex oxide thin-film heterostructures often exhibit magnetic properties different from those known for bulk constituents. This is due to the altered local structural and electronic environment at the interfaces, which affects the exchange coupling and magnetic ordering. The emergent magnetism at oxide interfaces can be controlled by ferroelectric polarization and has a strong effect on spin-dependent transport properties of oxide heterostructures, including magnetic and ferroelectric tunnel junctions. Here, using prototype La2/3Sr1/3MnO3/BaTiO3 heterostructures, we demonstrate that ferroelectric polarization of BaTiO3 controls the orbital hybridization and magnetism at heterointerfaces. We observe changes in the enhanced orbital occupancy and significant charge redistribution across the heterointerfaces, affecting the spin and orbital magnetic moments of the interfacial Mn and Ti atoms. Importantly, we find that the exchange coupling between Mn and Ti atoms across the interface is tuned by ferroelectric polarization from ferromagnetic to antiferromagnetic. Our findings provide a viable route to electrically control complex magnetic configurations at artificial multiferroic interfaces, taking a step toward low-power spintronics.

Enhanced Tunneling Magnetoresistance Effect via Ferroelectric Control of Interface Electronic/Magnetic Reconstructions

“…The electronic spin and orbital structure and reconstruction modulated by ferroelectric polarization at the interface of LSMO/BTO were studied by XMCD and XAS measurements directly. XAS and XMCD are surface and interface-sensitive approaches and provide direct measurements of element-specific valance state, magnetic moments, and magnetic coupling. ,,, Figure a,b shows the polarization dependence of XAS and XMCD at Mn and Ti L 2,3 edges. Apparently, when BTO polarization points toward the LSMO/BTO interface, both Mn and interfacial Ti move to lower valence states, indicating that the interface are electron-doped.…”

Direct Observation of Interface-Dependent Multidomain State in the BaTiO3 Tunnel Barrier of a Multiferroic Tunnel Junction Memristor

“…The interface , between the ferroelectric layer and ferromagnetic electrode is of major concern when we study multiferroic heterojunctions because it is crucial for the properties of thin film devices, especially the tunnel junction devices. , For classical ABO 3 perovskite heterostructures, the stacking sequence is determinant on the polarity of the interface, as well as other significant properties. ,,, Moreover, chemical diffusion is common at the interfaces of oxide heterostructures, and has a large effect on the corresponding performance; for example, the ferroelectric polarization of ferroelectric thin films and the magnetism properties of ferromagnetic thin films . For tunnel junctions, the behaviors of the interfaces are more complex since there are at least two interfaces working in the tunneling process.…”

“…17−24 In addition to domain configurations, oxygen vacancies may also be responsible for the memristive behavior of MFTJs, since the distribution of oxygen vacancies can modulate the ferroelectric/electrode interface barrier height. 25,26 The interface 27,28 between the ferroelectric layer and ferromagnetic electrode is of major concern when we study multiferroic heterojunctions because it is crucial for the properties of thin film devices, especially the tunnel junction devices. 29,30 For classical ABO 3 perovskite heterostructures, the stacking sequence is determinant on the polarity of the interface, as well as other significant properties.…”

Unusual Hole and Electron Midgap States and Orbital Reconstructions Induced Huge Ferroelectric Tunneling Electroresistance in BaTiO3/SrTiO3

“…Oxide heterostructures have attracted a lot of interest due to their rich exotic properties and their potential application. − For example, oxide heterostructures of polar insulating LaAlO 3 (LAO) on nonpolar insulating SrTiO 3 (STO) have shown two-dimensional electron gas (2DEG), ,,− insulator–metal transition, ,− magnetism, − electronic phase separation, − and superconductivity. − , Recently, theoretical studies have predicted that a ferroelectric insulating oxide such as (Pb,Ba)­TiO 3 on a nonpolar insulating oxide such as SrTiO 3 (BTO/STO), as a model system, may generate unusual two-dimensional hole gas (2DHG) and two-dimensional electron gas (2DEG) simultaneously, and its conductivity may be switched ON and OFF depending upon the ferroelectric polarization of the heterostructure. − Such an ability of switching the conductivity through spontaneous polarization in ferroelectric oxides may lead to a dramatic enhancement of tunneling electroresistance (TER), − which is crucial for ferroelectric tunnel junctions (FTJs). Indeed, a greatly enhanced TER (>10 4 ) has been observed in BaTiO 3 /SrTiO 3 (BTO/STO)-based system …”

“…21−23 Such an ability of switching the conductivity through spontaneous polarization in ferroelectric oxides may lead to a dramatic enhancement of tunneling electroresistance (TER), 24−26 which is crucial for ferroelectric tunnel junctions (FTJs). Indeed, a greatly enhanced TER (>10 4 ) has been observed in BaTiO 3 /SrTiO 3 (BTO/STO)-based system. 24 It is argued that an interplay between ferroelectricity and electronic transport at the oxide interface is much more complex than what could be inferred from classical electrostatic models, especially considering that there is no structural polar layer such as LaO + at the interface of BTO/STO films 27,28 This is mainly because at the interface and surface, electronic reconstruction, polarization, 2DHG, and 2DEG may involve and act as charge separation layers to stabilize ferroelectric polarization.…”