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Emergent magnetic phenomena at interfaces represent a frontier in materials science, pivotal for advancing technologies in spintronics and magnetic storage. In this Letter, we utilize a suite of advanced X-ray spectroscopic and scattering techniques to investigate emergent interfacial ferromagnetism in oxide superlattices composed of antiferromagnetic CaMnO3 and paramagnetic CaRuO3. Our findings demonstrate that ferromagnetism exhibits an asymmetric profile and may extend beyond the interfacial layer into multiple unit cells of CaMnO3. Complementary density functional calculations reveal that the interfacial ferromagnetism is driven by the double exchange mechanism, facilitated by charge transfer from Ru to Mn ions. Additionally, defect chemistry, particularly the presence of oxygen vacancies, can play a crucial role in modifying the magnetic moments at the interface, possibly leading to the observed asymmetry between the top and bottom CaMnO3 interfacial magnetic layers. Our findings underscore the potential of manipulating interfacial ferromagnetism through point defect engineering.

Employing the density functional theory (DFT) + Hubbard U approach, this work intends to explore the effects of strain and transition metal doping on the optical and electronic properties of SrVO3, a promising candidate for transparent conductors, and an alternative of indium tin oxide. By applying strain along three distinct crystallographic orientations, namely (010), (110), and (111), of the SrVO3 structure, alterations in the V d-bandwidth and changes in the electron–electron correlations are investigated in detail. Additionally, the effect of doping d-block transition metals (SrV0.75TM0.25O3) in tuning the properties of SrVO3 is studied within the DFT framework. Our density of states and transport calculations reveal that SrVO3 is metallic under compressive and tensile strain, and the resistivity increases under tensile strain compared to compressive strain. Furthermore, changes in the transport and optical properties are observed when doped with TMs from different d series. Among the doped systems studied, tungsten-doped SrVO3 exhibits lower optical absorption in the violet end of the spectrum, indicating its potential efficiency as a promising transparent conductor. Finally, the observed trends are explained based on changes in the electronic structure of SrVO3 under strain and doping. [ABSTRACT FROM AUTHOR]

Emergent magnetic phenomena at interfaces represent a frontier in materials science, pivotal for advancing technologies in spintronics and magnetic storage. In this Letter, we utilize a suite of advanced X-ray spectroscopic and scattering techniques to investigate emergent interfacial ferromagnetism in oxide superlattices composed of antiferromagnetic CaMnO 3 and paramagnetic CaRuO 3 . Our findings demonstrate that ferromagnetism exhibits an asymmetric profile and may extend beyond the interfacial layer into multiple unit cells of CaMnO 3 . Complementary density functional calculations reveal that the interfacial ferromagnetism is driven by the double exchange mechanism, facilitated by charge transfer from Ru to Mn ions. Additionally, defect chemistry, particularly the presence of oxygen vacancies, can play a crucial role in modifying the magnetic moments at the interface, possibly leading to the observed asymmetry between the top and bottom CaMnO 3 interfacial magnetic layers. Our findings underscore the potential of manipulating interfacial ferromagnetism through point defect engineering.

We review recent advances in strongly correlated oxides as thermoelectric materials in pursuit of energy harvesting. We discuss two topics: one is the enhancement of the ordinary thermoelectric properties by controlling orbital degrees of freedom and orbital fluctuation not only in bulk but also at the interface of correlated oxides. The other topic is the use of new phenomena driven by spin-orbit coupling (SOC) of materials. In 5d electron oxides, we show some SOC-related transport phenomena, which potentially contribute to energy harvesting. We outline the current status and a future perspective of oxides as thermoelectric materials.

In contrast to perovskites that share only common corners of cation‐occupied octahedra, binary‐oxides in addition share edges and faces increasing the versatility for tuning the properties and functionality of reduced dimensionality systems of strongly correlated oxides. This approach for tuning the electronic structure is based on the ability of X‐ray spectroscopy methods to monitor the creation and transformation of occupied and unoccupied electronic states produced by interface coupling and lattice distortions. X‐ray diffraction reveals a new range of structural metastability in (TiO2)m/(VO2)m/TiO2(001) superlattices with m = 1, 3, 5, 20, 40, and electrical transport measurements show metal insulator transition (MIT) behavior typically associated with presence of high oxygen vacancy concentrations. However, X‐ray absorption spectroscopy (XAS) at the Ti and V L3,2‐edge and resonant inelastic X‐ray scattering (RIXS) at the Ti and V L3‐edge show no excitations characteristic of oxygen vacancy induced valance change in V and negligible intensities in Ti RIXS. The unexpected absence of oxygen vacancy related states in the X‐ray spectroscopy data suggests that superlattice fabrication is capable of suppressing oxygen vacancy formation while still affording a wide tunability range of the MIT. Achieving a wide range of MIT tunability while reducing or eliminating oxygen vacancies that are detrimental to electrical properties is highly desirable for technological applications of strongly correlated oxides. [ABSTRACT FROM AUTHOR]

Magnetic properties of single perovskite-structure epitaxial film are reported to have layered distribution recently. However, the different responses of spin configurations in individual layers to the variations of temperature and strain state, especially the subtle response of layered film due to structural phase transformation of SrTiO 3 (STO) substrate around 105 K, have not been revealed completely. Drastic drop and concomitant abnormal increase of remnant magnetic moments (REM) and coercivity of low-doped La 1-x Sr x MnO 3 (x = 0.175) /SrTiO 3 film were observed around 105 K only in the in-plane direction, and layered magnetic structures were further inferred based on investigation of microstructure, strain distribution and chemical inhomogeneity. Abnormal change of magnetic properties around 105 K was discussed by a three-layer model, in which softer ferromagnetic layer was supposed to form in the middle layer of strain-induced layered structure, and the spin configuration of middle layer underwent non-synchronous transformation relative to other parts of the film, which may be attributed to the change of in-plane strain inside the film around 105 K. Our work reveals the variation of individual magnetic layers with the increase of temperature through utilizing the remnant magnetic field in measuring system, and the abrupt reversal of spin configurations at the intermediate layer can also serve the design of novel spintronics devices in the future. Image, graphical abstract [ABSTRACT FROM AUTHOR]

We review recent advances in strongly correlated oxides as thermoelectric materials in pursuit of energy harvesting. We discuss two topics: one is the enhancement of the ordinary thermoelectric properties by controlling orbital degrees of freedom and orbital fluctuation not only in bulk but also at the interface of correlated oxides. The other topic is the use of new phenomena driven by spin-orbit coupling (SOC) of materials. In 5d electron oxides, we show some SOC-related transport phenomena, which potentially contribute to energy harvesting. We outline the current status and a future perspective of oxides as thermoelectric materials. [ABSTRACT FROM AUTHOR]

In recent years Resistive Random Access Memory (RRAM) is emerging as the most promising candidate to substitute the present Flash Technology in the non-volatile memory market. RRAM are based on the Resistive Switching (RS) effect, where a change in the resistance of the material can be reversibly induced upon the application of an electric field. In this sense, strongly correlated complex oxides present unique intrinsic properties and extreme sensitivity to external perturbations, which make them suitable for the nanoelectronics of the future. In particular, metallic complex oxides displaying metal-insulator transition (MIT) are very attractive materials for applications and are barely explored as RS active elements. In this work, we analyze the RS behavior of different films belonging to three different families of metallic perovskites: LaSrMnO, YBaCuO and NdNiO. We demonstrate that these mixed electronic-ionic conductors undergo a metal-insulator transition upon the application of an electric field, being able to transform the bulk volume. This volume RS is different in nature from interfacial or filamentary type and opens new possibilities of robust device design. As an example, we present a proof-of-principle result from a 3-Terminal configuration with multilevel memory states. [ABSTRACT FROM AUTHOR]

Freestanding films provide a versatile platform for materials engineering thanks to additional structural motifs not found in films with a substrate. A ubiquitous example is wrinkles, yet little is known about how they can develop over as fast as a few picoseconds due to a lack of experimental probes to visualize their dynamics in real time on the nanoscopic scale. Here, we use time-resolved electron diffraction to directly observe light-activated wrinkling formation in freestanding La 2/3 Ca 1/3 MnO 3 films. Via a "lock-in" analysis of oscillations in the diffraction peak position, intensity, and width, we quantitatively reconstructed how wrinkles develop on the time scale of lattice vibration. Contrary to the common assumption of fixed boundary conditions, we found that wrinkle development is associated with ultrafast delamination at the film boundaries. Our work provides a generic protocol to quantify wrinkling dynamics in freestanding films and highlights the importance of the film-substrate interaction in determining the properties of freestanding structures.

We demonstrate a novel pathway to control and stabilize oxygen vacancies in complex transition-metal oxide thin films. Using atomic layer-by-layer pulsed laser deposition (PLD) from two separate targets, we synthesize high-quality single-crystalline CaMnO3 films with systematically varying oxygen vacancy defect formation energies as controlled by coherent tensile strain. The systematic increase of the oxygen vacancy content in CaMnO3 as a function of applied in-plane strain is observed and confirmed experimentally using high-resolution soft X-ray absorption spectroscopy (XAS) in conjunction with bulk-sensitive hard X-ray photoemission spectroscopy (HAXPES). The relevant defect states in the densities of states are identified and the vacancy content in the films quantified using the combination of first-principles theory and core-hole multiplet calculations with holistic fitting. Our findings open up a promising avenue for designing and controlling new ionically active properties and functionalities of complex transition-metal oxides via strain-induced oxygen-vacancy formation and ordering. [ABSTRACT FROM AUTHOR]

The article presents a study focusing on electronically phase separated materials and the multimodal responses of self-organized circuitry in them. Topics discussed include the voltage versus current response analysis; the single crystal films used in the study; and the functions of magnetic field. Also mentioned are resistor-capacitor (RC) circuits, and the single crystal oxides used in devices.

The characteristic aspect of strongly correlated oxides systems is the strong coupling between the structural, electronic and magnetic properties. A small change in one property can produce a large change in another. Controllable surface tuning provides the opportunity to study how structural, electronic, and magnetic properties respond to the broken symmetry and opens avenues for exploration of completely new physical properties. The extreme sensitivity of properties to external chemical and physical stimuli makes in situ characterization a requirement for controlled tuning of complex correlated materials. This paper reviews some recent progress in in situ observations and tuning of physical and chemical phenomena on the surfaces of strongly correlated oxides thin films and crystals, including atomic-level structural studies, control, and tuning of the physical properties. [ABSTRACT FROM AUTHOR]

Keywords: binary oxide superlattices; metal insulator transitions; pulsed laser deposition; strongly correlated oxides; X-ray spectroscopy EN binary oxide superlattices metal insulator transitions pulsed laser deposition strongly correlated oxides X-ray spectroscopy 1 1 1 12/17/20 20201215 NES 201215 The fabrication of binary oxide superlattices is undertaken as a general approach for exploring novel concepts and phenomena in reduced dimensionality systems of strongly correlated oxides. In article number 2004914, Gyula Eres, Milan Radovic, Thorsten Schmitt, and co-workers achieve a wide range of tunability of the metal insulator transition in VO SB 2 sb while reducing oxygen vacancy formation that is detrimental to electrical properties. Binary oxide superlattices, metal insulator transitions, pulsed laser deposition, strongly correlated oxides, X-ray spectroscopy. [Extracted from the article]

Memristive devices are attracting a great attention for memory, logic, neural networks, and sensing applications due to their simple structure, high density integration, low-power consumption, and fast operation. In particular, multi-terminal structures controlled by active gates, able to process and manipulate information in parallel, would certainly provide novel concepts for neuromorphic systems. In this way, transistor-based synaptic devices may be designed, where the synaptic weight in the postsynaptic membrane is encoded in a source-drain channel and modified by presynaptic terminals (gates). In this work, we show the potential of reversible field-induced metal-insulator transition (MIT) in strongly correlated metallic oxides for the design of robust and flexible multi-terminal memristive transistor-like devices. We have studied different structures patterned on YBa2Cu3O7−δ films, which are able to display gate modulable non-volatile volume MIT, driven by field-induced oxygen diffusion within the system. The key advantage of these materials is the possibility to homogeneously tune the oxygen diffusion not only in a confined filament or interface, as observed in widely explored binary and complex oxides, but also in the whole material volume. Another important advantage of correlated oxides with respect to devices based on conducting filaments is the significant reduction of cycle-to-cycle and device-to-device variations. In this work, we show several device configurations in which the lateral conduction between a drain-source channel (synaptic weight) is effectively controlled by active gate-tunable volume resistance changes, thus providing the basis for the design of robust and flexible transistor-based artificial synapses. [ABSTRACT FROM AUTHOR]

Artificial complex-oxide heterostructures containing ultrathin buried layers grown along the pseudocubic [111] direction have been predicted to host a plethora of exotic quantum states arising from the graphene-like lattice geometry and the interplay between strong electronic correlations and band topology. To date, however, electronic-structural investigations of such atomic layers remain an immense challenge due to the shortcomings of conventional surface-sensitive probes with typical information depths of a few angstroms. Here, we use a combination of bulk-sensitive soft X-ray angle-resolved photoelectron spectroscopy (SX-ARPES), hard X-ray photoelectron spectroscopy (HAXPES), and state-of-the-art first-principles calculations to demonstrate a direct and robust method for extracting momentum-resolved and angle-integrated valence-band electronic structure of an ultrathin buckled graphene-like layer of NdNiO 3 confined between two 4-unit cell-thick layers of insulating LaAlO 3 . The momentum-resolved dispersion of the buried Ni d states near the Fermi level obtained via SX-ARPES is in excellent agreement with the first-principles calculations and establishes the realization of an antiferro-orbital order in this artificial lattice. The HAXPES measurements reveal the presence of a valence-band bandgap of 265 meV. Our findings open a promising avenue for designing and investigating quantum states of matter with exotic order and topology in a few buried layers.

Heteroepitaxial coupling at complex oxide interfaces presents a powerful tool for engineering the charge degree of freedom in strongly correlated materials, which can be utilized to achieve tailored functionalities that are inaccessible in the bulk form. Here, the charge-transfer effect between two strongly correlated oxides, Sm 0.5 Nd 0.5 NiO 3 (SNNO) and La 0.67 Sr 0.33 MnO 3 (LSMO), is exploited to realize a giant enhancement of the ferroelectric field effect in a prototype Mott field-effect transistor. By switching the polarization field of a ferroelectric Pb(Zr,Ti)O 3 (PZT) gate, nonvolatile resistance modulation in the Mott transistors with single-layer SNNO and bilayer SNNO/LSMO channels is induced. For the same channel thickness, the bilayer channels exhibit up to two orders of magnitude higher resistance-switching ratio at 300 K, which is attributed to the intricate interplay between the charge screening at the PZT/SNNO interface and the charge transfer at the SNNO/LSMO interface. X-ray absorption spectroscopy and X-ray photoelectron spectroscopy studies of SNNO/LSMO heterostructures reveal about 0.1 electron per 2D unit cell transferred between the interfacial Mn and Ni layers, which is corroborated by first-principles density functional theory calculations. The study points to an effective strategy to design functional complex oxide interfaces for developing high-performance nanoelectronic and spintronic applications., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Transition metal oxides having a perovskite structure form a wide and technologically important class of compounds. In these systems, ferroelectric, ferromagnetic, ferroelastic, or even orbital and charge orderings can develop and eventually coexist. These orderings can be tuned by external electric, magnetic, or stress field, and the cross-couplings between them enable important multifunctional properties, such as piezoelectricity, magneto-electricity, or magneto-elasticity. Recently, it has been proposed that additional to typical fields, the chemical potential that controls the concentration of ion vacancies in these systems may reveal an efficient alternative parameter to further tune their properties and achieve new functionalities. In this study, concretizing this proposal, the authors show that the control of the content of oxygen vacancies in perovskite thin films can indeed be used to tune their magnetic properties. Growing PrVO 3 thin films epitaxially on an SrTiO 3 substrate, the authors reveal a concrete pathway to achieve this effect. The authors demonstrate that monitoring the concentration of oxygen vacancies through the oxygen partial pressure or the growth temperature can produce a substantial macroscopic tensile strain of a few percent. In turn, this strain affects the exchange interactions, producing a nontrivial evolution of Néel temperature in a range of 30 K., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)