Hidden Interface Driven Exchange Coupling in Oxide Heterostructures

Chen, Aiping; Wang, Qiang; Fitzsimmons, M. R.; Enriquez, Erik; Weigand, M.; Harrell, Zach; McFarland, B. K.; Lu, Xiaofeng; Dowden, P. C.; MacManus‐Driscoll, Judith L.; Yarotski, D. A.; Jia, Q. X.

doi:10.1002/adma.201700672

Cited by 22 publications

(21 citation statements)

References 59 publications

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“…On this basis, similar negative values of µ 0 H E as decreasing the Cr 2 O 3 weight percentage in the composites would uncover this type of exchange bias. However, the crossover from negative to positive values of µ 0 H E shown in Figure d indicates the coexistence of different coupling mechanisms, given the fact that no external stimuli like temperature, electric or magnetic fields were used to influence this crossover phenomenology . Appropriately, an exchange bias mechanism with positive values of µ 0 H E associated to the interface between nanoparticles of the two different oxides in the composites (as sketched in Figure b) would increase its value as increasing the area of this interface, that is, as increasing the weight percentage of the cobalt ferrite (or decreasing the percentage of the chromium oxide) in the final composites.…”

Section: Resultsmentioning

confidence: 97%

“…This implies a frustrated rather than a canted situation of the uncompensated spins at the surface of the chromium oxide nanoparticles once arranged into the composites. Since no covalent bonds are established between the atoms at the surface of the spinel ferrite and those at the surface of the chromium oxide, it is the increased frustration in a consequently more glassy system, caused by the increased dipolar interactions upon increasing the percentage of cobalt ferrite, what forces the spin layer to change from a canted to a frustrated condition . This can be also associated with the shifts in the phonon frequencies measured by Raman spectroscopy, as changing the magnetic configuration at the interface.…”

Section: Resultsmentioning

confidence: 99%

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Spin Frustration Drives Exchange Bias Sign Crossover in CoFe₂O₄–Cr₂O₃ Nanocomposites

Testa‐Anta

Rivas‐Murias

Salgueiriño

2019

Adv Funct Materials

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A combined Raman spectroscopy and magnetometry study of CoFe 2 O 4 -Cr 2 O 3 nanocomposites demonstrates the presence of spin-phonon interactions and exchange bias at the interface between the ferrimagnetic CoFe 2 O 4 and the antiferromagnetic and magnetoelectric Cr 2 O 3 phases. The pinned layer of uncompensated spins at the surface of the chromium oxide nanocrystals provides a source of unidirectional anisotropy and changes the sign of the exchange bias when transitioning from a canted to a frustrated situation, that is, as increasing the percentage of CoFe 2 O 4 or decreasing the percentage of Cr 2 O 3 in the composites. This assessment of the distinctive interfaces attained in the final oxide heterostructures offers a prospective route for hybrid materials which uphold a magnetoelectric effect.

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Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 99%

Spin Frustration Drives Exchange Bias Sign Crossover in CoFe₂O₄–Cr₂O₃ Nanocomposites

Testa‐Anta

Rivas‐Murias

Salgueiriño

2019

Adv Funct Materials

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“…Even in the mostly studied manganites La x Sr 1− x MnO 3 (LSMO) films epitaxially grown on STO substrates, different mechanisms have been proposed to explain the anomalous interfacial properties. For instance, epitaxial strain, interfacial chemistry, charge discontinuity, octahedral rotation, and off‐stoichiometry have been proposed to explain the observed experimental results . In order to understand 2DEG at oxide interfaces, different mechanisms such as cation off‐stoichiometry, surface reconstruction, oxygen vacancies, cation intermixing, and structural distortions have been proposed.…”

Section: Introductionmentioning

confidence: 99%

Metal Oxide Nanocomposites: A Perspective from Strain, Defect, and Interface

et al. 2018

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Complex metal oxides, which show a variety of functional properties such as ferromagnetism, ferroelectricity, multi-ferroelectricity, superconductivity, and ionic conduction, have attracted much attention in the past decades. These exotic physical properties arise from a complex hierarchy of competing interactions among spin, charge, orbital, and lattice degrees of freedom. The development of advanced characterization techniques such as electron microscopy, neutron scattering, synchrotron scattering and imaging, spectroscopy at high magnetic fields, and others has enabled us to study the interactions among these degrees of freedom coupled with strain, defect, and interface Vertically aligned nanocomposite thin films with ordered two phases, grown epitaxially on substrates, have attracted tremendous interest in the past decade. These unique nanostructured composite thin films with large vertical interfacial area, controllable vertical lattice strain, and defects provide an intriguing playground, allowing for the manipulation of a variety of functional properties of the materials via the interplay among strain, defect, and interface. This field has evolved from basic growth and characterization to functionality tuning as well as potential applications in energy conversion and information technology. Here, the remarkable progress achieved in vertically aligned nanocomposite thin films from a perspective of tuning functionalities through control of strain, defect, and interface is summarized. Thin FilmsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.201803241. 12 11 12where c 11 and c 12 are elastic moduli of the film material. Epitaxial strain gradually changes with film thickness in perovskite manganites. Figure 3 shows reciprocal space mapping or RSM (103) of La 0.7 Ca 0.3 MnO 3 (LCMO) films on STO (001) substrates. It captures the gradual strain relaxation process with increasing film thickness in manganite thin films. When the film is very thin, the interface is coherent with

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“…On the other hand, lack of atomic-scale studies limits the transferability of experimental findings and does not provide useful input for or direct comparison with first-principles calculations. For example, Lee et al (32) and Chen et al (33) reported "hidden magnetic properties" in LSMO/STO heterostructures. The former work proposes mixed Mn 3+ /Mn 4+ oxidation state, and possible electronic reconstruction at the interface as the reason behind the phenomena, while the latter relates unexpected magnetic properties to the presence of an interfacial AFM-coupled pinned magnetic layer.…”

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confidence: 99%

Atomic-scale determination of spontaneous magnetic reversal in oxide heterostructures

Saghayezhian

Kouser

Wang

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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Interfaces between transition metal oxides are known to exhibit emerging electronic and magnetic properties. Here we report intriguing magnetic phenomena for La 2/3 Sr 1/3 MnO 3 films on an SrTiO 3 (001) substrate (LSMO/STO), where the interface governs the macroscopic properties of the entire monolithic thin film. The interface is characterized on the atomic level utilizing scanning transmission electron microscopy and electron energy loss spectroscopy (STEM-EELS), and density functional theory (DFT) is employed to elucidate the physics. STEM-EELS reveals mixed interfacial stoichiometry, subtle lattice distortions, and oxidation-state changes. Magnetic measurements combined with DFT calculations demonstrate that a unique form of antiferromagnetic exchange coupling appears at the interface, generating a novel exchange spring-type interaction that results in a remarkable spontaneous magnetic reversal of the entire ferromagnetic film, and an inverted magnetic hysteresis, persisting above room temperature. Formal oxidation states derived from electron spectroscopy data expose the fact that interfacial oxidation states are not consistent with nominal charge counting. The present work demonstrates the necessity of atomically resolved electron microscopy and spectroscopy for interface studies. Theory demonstrates that interfacial nonstoichiometry is an essential ingredient, responsible for the observed physical properties. The DFT-calculated electrostatic potential is flat in both the LSMO and STO sides (no internal electric field) for both Sr-rich and stoichiometric interfaces, while the DFT-calculated charge density reveals no charge transfer/ accumulation at the interface, indicating that oxidation-state changes do not necessarily reflect charge transfer and that the concept of polar mismatch is not applicable in metal−insulator polar−nonpolar interfaces. magnetism | thin films | electron microscopy | oxide interfaces | density functional theory T ransition metal oxides (TMOs) exhibit a wide range of electrical, magnetic, and optical properties largely because they can be easily alloyed and the 10 slots in the transition metal atom d orbitals allow for very diverse spin arrangements. Adding strong electron−lattice coupling and easily formed oxygen vacancies to this mix, the result is a large number of coupled degrees of freedom. Therefore, it is not surprising that TMO heterostructures exhibit highly unusual behavior, induced by interfaces between different oxides where symmetry discontinuities occur, leading to properties that are absent in bulk (1-5). A wellknown example is the LaAlO 3 /SrTiO 3 (001) heterostructure, where a 2D electron gas with high mobility forms at the interface between two insulating oxides (6), including the appearance of superconductivity (7) and background ferromagnetic (FM) ordering (8). In many cases, the symmetry discontinuity at the interface strongly modifies the transition metal−oxygen octahedra network, inducing changes in local structure (bond geometry) and local stoichiometry. Thes...

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Hidden Interface Driven Exchange Coupling in Oxide Heterostructures

Cited by 22 publications

References 59 publications

Spin Frustration Drives Exchange Bias Sign Crossover in CoFe₂O₄–Cr₂O₃ Nanocomposites

Spin Frustration Drives Exchange Bias Sign Crossover in CoFe₂O₄–Cr₂O₃ Nanocomposites

Metal Oxide Nanocomposites: A Perspective from Strain, Defect, and Interface

Atomic-scale determination of spontaneous magnetic reversal in oxide heterostructures

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Hidden Interface Driven Exchange Coupling in Oxide Heterostructures

Cited by 22 publications

References 59 publications

Spin Frustration Drives Exchange Bias Sign Crossover in CoFe2O4–Cr2O3 Nanocomposites

Spin Frustration Drives Exchange Bias Sign Crossover in CoFe2O4–Cr2O3 Nanocomposites

Metal Oxide Nanocomposites: A Perspective from Strain, Defect, and Interface

Atomic-scale determination of spontaneous magnetic reversal in oxide heterostructures

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Product

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Spin Frustration Drives Exchange Bias Sign Crossover in CoFe₂O₄–Cr₂O₃ Nanocomposites

Spin Frustration Drives Exchange Bias Sign Crossover in CoFe₂O₄–Cr₂O₃ Nanocomposites