Thickness Dependent Properties in Oxide Heterostructures Driven by Structurally Induced Metal–Oxygen Hybridization Variations

Liao, Zhaoliang; Gauquelin, Nicolas; Green, Robert J.; Macke, S.; Gonnissen, J.; Thomas, S. M.; Zhong, Zhicheng; Li, Lin; Si, Liang; Aert, Sandra Van; Hansmann, P.; Held, Karsten; Xia, Jing; Verbeeck, Johan; Tendeloo, Gustaaf Van; Sawatzky, G. A.; Koster, Gertjan; Huijben, Mark; Rijnders, Guus

doi:10.1002/adfm.201606717

Cited by 64 publications

(68 citation statements)

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“…Rather, it appears that octahedral rotations can propagate from the NGO substrate into the NNO film and dictate its Ni‐O‐Ni bond angle. Similar phenomena have been observed in several other materials systems, altering the rotations in the oxygen sublattice for several unit cells near the interface …”

Section: Resultssupporting

confidence: 82%

Interfacial Octahedral Manipulation Imparts Hysteresis‐Free Metal to Insulator Transition in Ultrathin Nickelate Heterostructure

Dong

Luo

et al. 2019

Adv Materials Inter

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electric and magnetic properties. [1][2][3][4] Among them, the rare earth nickelates (RNiO 3 , where R is a trivalent rare earth ion) have attracted much attention as model systems for the metal-insulator transition (MIT). [5][6][7][8] Catalan [9] summarized the results for RNiO 3 with a phase diagram showing that the nickelates are generally orthorhombic metals above the MIT temperature (T MI ) and monoclinic insulators below T MI. The strong relationship between structure and electronic properties has led to the development of several methods for modulating the MIT of RNiO 3 , e.g., strain engineering, [10] chemical doping, [11] and multilayer fabrication, [5] suggesting an array of applications in electronic and optical devices with controllable switching characteristics.The origin of the MIT has long been a subject of interest in the condensed matter sciences, and several models have been proposed. [12,13] A key parameter is the Ni-O-Ni bond angle (ϴ), which is known to affect T MI : a 180° angle maintains the 3d-2p-3d orbital overlap, resulting in metallic properties, whereas smaller angles lead to Much like epitaxial strain, engineering oxygen octahedral rotations (OORs) in perovskite oxide thin films can be a powerful means of manipulating their physical and chemical properties. Here, it is demonstrated that the fundamental character of the metal-insulator transition (MIT) can be sensitively controlled by the structure of the oxygen sublattice for NdNiO 3 thin films grown epitaxially on NdGaO 3 (110) substrates. The MIT is sharp and hysteretic for a Ni-O-Ni bond angle of 154.0° (6 nm thick film) like the bulk behavior, while it is diffuse and largely nonhysteretic for a bond angle of 149.5° (3 nm thick film), stemming from the smaller bond angle of the NdGaO 3 substrate. Using synchrotron X-ray diffraction to quantify the geometric framework of the oxygen sublattice, it is found that the influence of the substrate OORs propagates and decays after a few nanometers into the ultrathin film. The sublattice structure in the 6 nm thick film is similar to that for bulk NdNiO 3 , leading to the sharp and hysteretic MIT.

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Section: Resultssupporting

confidence: 82%

Interfacial Octahedral Manipulation Imparts Hysteresis‐Free Metal to Insulator Transition in Ultrathin Nickelate Heterostructure

Dong

Luo

et al. 2019

Adv Materials Inter

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“…It is worth noting that the switching of magnetic easy axis occurs at the thinner LSMO/NGO layers with t LSMO ≈ 6−9 u.c . The easy axis along the b ‐axis may be understood in terms of θ‐mediated Mn 3d –O 2p orbital hybridization, it however cannot explain the enhanced MAE. If θ dominates the magnetic anisotropy, the large MAE corresponds to the large difference between θ a and θ b , where θ a and θ b stand for the BOB bond angle along the a and b axes, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…The bulk LSMO possesses a rhombohedral lattice with a − a − a − rotation and MnOMn bond angle around 166°, while the bulk NGO exhibits an orthorhombic lattice with c + a − a − rotation and GaOGa bond angle around 151°−156° . While previous works have demonstrated the switching of magnetic easy axis mediated by the interfacial layer, our aim is to increase MAE via different interface‐engineering approaches. The first approach is to change the LSMO layer thickness, t LSMO , as indicated in Figure a.…”

Section: Resultsmentioning

confidence: 99%

“…Rajapitamahuni et al used a ferroelectric PbZr 0.2 Ti 0.8 O 3 layer to tune the Mn 3d orbital occupancy in an adjacent La 0.8 Sr 0.2 MnO 3 layer to obtain a 22% improvement on lateral magnetic anisotropy energy (MAE) . Through the oxygen octahedral coupling across the heterointerface, Liao et al were able to change the MnOMn bond angle θ and thus the hybridization between Mn 3d and O 2p (Mn 3d –O 2p ) orbitals, triggering the switch of lateral magnetic easy axis . To date, although the tunability of magnetic anisotropy has been well documented, there remain two unsolved critical questions.…”

Section: Introductionmentioning

confidence: 99%

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Enhanced Magnetic Anisotropy and Orbital Symmetry Breaking in Manganite Heterostructures

Chen

Huang

et al. 2019

Adv Funct Materials

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Manipulating magnetic anisotropy in complex oxide heterostructures has attracted much attention. Here, three interface‐engineering approaches are applied to address two general issues with controlling magnetic anisotropy in the La2/3Sr1/3MnO3 heterostructure. One is the paradox arising from the competition between Mn3d–O2p orbital hybridization and MnO6 crystal field. The other is the interfacial region where the nonuniform MnO bond length d and MnOMn bond angle θ disturb the structural modulation. When the interfacial region is suppressed in the interface‐engineered samples, the lateral magnetic anisotropy energy is increased eighteen times. The d‐mediated anisotropic crystal filed that overwhelms the orbital hybridization causes the lateral symmetry breaking of the Mn 3dx2−y2 orbital, resulting in enhanced magnetic anisotropy. This is different from the classic Jahn–Teller effect where the lateral symmetry is always preserved. Moreover, the quantitative analysis on X‐ray linear dichroism data suggests a direct correlation between Mn 3dx2−y2 orbital symmetry breaking and magnetic anisotropy energy. The findings not only advance the understanding of magnetic anisotropy in manganite heterostructures but also can be extended to other complex oxides and perovskite materials with correlated degrees of freedom.

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“…Ferroelectric interfaces are key elements for the functionality of these heterostructures. Their underlying phenomenology is determined by the chemistry of the specific materials, their thickness, as well as the design and quality of interfaces [39][40][41][42][43]. At the interface with a ferroelectric the polar distortions are perturbed, the local strain, bonding across the interface and the built-in electric field promote charge transfers and space charge build-up.…”

Section: Introductionmentioning

confidence: 99%

Designing functional ferroelectric interfaces from first-principles: dipoles and band bending at oxide heterojunctions

et al. 2019

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The fundamental phenomena at ferroelectric interfaces have been the subject of thorough theoretical and computational studies due to their usefulness in a large variety of emergent electronic devices, solar cells and catalysts. Ferroelectricity determines interface band-bending and shifts in electron energies, which can be beneficial or detrimental to device performance. However, the underlying mechanisms are still the subject of debate and investigation, as a deeper understanding of the electrochemistry is required to develop bona fide design principles for functional ferroelectric surfaces and interfaces. Here, using first principles calculations within the GGA+U formalism, we investigate the problem of band alignment in non-defective, asymmetric SrRuO 3 /PbTiO 3 /SrRuO 3 capacitors with ultra-thin ferroelectric layers. The effects of the dielectric size on the polar distortion stability and interface-specific properties are analyzed. It is shown that the critical size of the dielectric for polarization switching is 2 nm » (5 PbTiO 3 u.c.). Below this limit there is no bulk-like region in the dielectric, the space charge accumulated at interfaces leads to the presence of gap states in the whole PbTiO 3 layer and ferroelectricity vanishes. We draw the band alignment diagrams as given by the band line-up and band structure terms, as well as by taking Ti 3s semi-core states as reference. In the ferroelectric structures, both approaches predict a strong effect of band-bending on the type of contact, Schottky or Ohmic, at the asymmetric interfaces. The effect of interface states on the interface dipole amplitude and band alignment is discussed.

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Thickness Dependent Properties in Oxide Heterostructures Driven by Structurally Induced Metal–Oxygen Hybridization Variations

Cited by 64 publications

References 50 publications

Interfacial Octahedral Manipulation Imparts Hysteresis‐Free Metal to Insulator Transition in Ultrathin Nickelate Heterostructure

Interfacial Octahedral Manipulation Imparts Hysteresis‐Free Metal to Insulator Transition in Ultrathin Nickelate Heterostructure

Enhanced Magnetic Anisotropy and Orbital Symmetry Breaking in Manganite Heterostructures

Designing functional ferroelectric interfaces from first-principles: dipoles and band bending at oxide heterojunctions

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