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Compositional tuning of correlations between electrons, spins, and lattices in solids is a key strategy for exploring quantum phenomena. In contrast to uniform chemical substitutions that are widely used for the compositional tunings, continuous variations in compositions along a given direction of materials (composition gradients) are expected to modulate translational crystal symmetries and electronic band structures, leading to unique properties not seen in homogeneously substituted materials. Preparing compositionally graded materials, however, is still challenging as it requires elaborate fabrication processes, and how composition gradients affect materials' properties remains elusive. Here, we show that composition gradients can be made by simply depositing films under continuously varying oxygen pressures by pulsed laser deposition. Applying this technique to the inverse-spinel-structured ferrimagnet NiCo2O4, we found that composition gradients in NiCo2O4 epitaxial films tune the magnetic anisotropy and stabilize the magnetizations modulated along the gradient, which are not seen in compositionally uniform films. The spatially modulated magnetization can also be reversed in controlled manners through distinct antiferromagnetically coupled magnetization configurations in the single material. Our results demonstrate the potential of composition gradients to tune materials' properties and explore a new class of materials with added functionalities. [ABSTRACT FROM AUTHOR]

We investigated the influence of oxygen vacancies on the magnetic and transport properties of ferrimagnetic NiCo2O4 (NCO) epitaxial films. Oxygen vacancies were introduced by annealing under reducing atmospheres NCO films whose cation composition was close to the stoichiometric one. We find that annealing NCO films under the vacuum reduces their magnetizations and increases their electrical resistivities. The perpendicular magnetic anisotropy, on the other hand, is almost unaffected by annealing treatments. X-ray absorption spectroscopy shows that oxygen vacancies introduced in NCO films preferentially lower the Ni valence state while leaving the Co valence state unchanged. The lowering in the Ni valence state explains the reduced magnetizations and the increased resistivities for the films annealed under the vacuum. On the other hand, the Co valence state, which dominantly determines the orbital magnetic moments responsible for magnetic anisotropy, is insensitive to oxygen vacancies. Therefore, the perpendicular magnetic anisotropy is maintained even when the oxygen vacancies are introduced. [ABSTRACT FROM AUTHOR]

We grew SnO2 thin films on (001) YSZ substrates by a mist chemical vapor deposition (mist CVD) method and investigated their structural properties by measuring synchrotron x-ray diffraction. We found that the structural phases of the films depend on the growth temperature. SnO2 deposited at 400 °C was found to be epitaxially grown on the substrate and to have the high-pressure-stabilized structure [i.e., columbite structure with the (100)-orientation]. On the other hand, films deposited at 700 °C have a mixture of the epitaxially grown columbite structure and a polycrystalline rutile structure. We also found that while films deposited at both temperatures are grown in island-growth manners, the size of the islands in the initial stage of growth depends on the growth temperature. The islands of the films grown at 400 °C have diameters of 59 nm ± 10 nm, while the islands of the films grown at 700 °C have diameters 2 times larger (110 nm ± 16 nm). These observations indicate that the coalescence of the deposited mist particles resulting from the higher temperature growth, which makes the island larger, leads to partial relaxation of the substrate-induced strain. This explains why the films deposited at 700 °C consist of a mixture of the columbite and rutile structures. Our results highlight the significance of the growth-temperature-dependent coalescence and its induced strain relaxation as the factor determining the structural phase of mist-CVD-grown films. [ABSTRACT FROM AUTHOR]

We carried out the synchrotron X-ray diffraction measurements and investigated the oxygen octahedral distortions in compressively strained SrRuO3 epitaxial thin films on NdGaO3 substrates. We observed half-order Bragg reflections originating from the RuO6 octahedral distortions accommodated in the compressively strained films. Our structural analysis shows that the RuO6 octahedra are elongated along the out-of-plane direction and are rotated in the out-of-phase manner only about the out-of-plane direction. The RuO6 rotation angle γrot is 10.9° ± 1.2°, which is larger than that in the bulk SrRuO3. The results indicate that the substrate-induced compressive strain enhances the out-of-plane rotations while strongly suppressing the in-plane rotations. In fact, the half-order Bragg reflections arising from the octahedral rotations about the in-plane direction are found to be weak and broad, implying that the in-plane rotations exist only in the interface region, not in the entire film. This indicates that while the in-plane octahedral rotation propagates through the interfacial octahedral connections into the film, its propagation decays within the interface region because of the compressive strain. Our results indicate that both the substrate-induced strain and the interfacial octahedral connection play important roles in determining the octahedral distortions accommodated in the strained SrRuO3 films. [ABSTRACT FROM AUTHOR]

We grew epitaxial thin films of hematite (α-Fe2O3) on (0 0 0 1) Al2O3 substrates by pulsed laser deposition and investigated their magnetic properties. α-Fe2O3 films grown at lower temperatures are found to undergo the Morin transition at higher temperatures, implying that lowering the growth temperature and managing lattice defects associated with strain relaxation are key to realizing Morin transition. We also characterized films' magnetic properties by spin Hall magnetoresistance (SMR). We show that tri-axial magnetic anisotropy can be detected as SMR features having a 60° period with respect to in-plane magnetic field rotations. Furthermore, a large change in SMR ratio associated with Néel vector re-orientation due to Morin transition is seen. Details of SMR properties for α-Fe2O3 films and their analysis results, including the influence of the fabrication process on SMR behaviors, are discussed. [ABSTRACT FROM AUTHOR]

To electrochemically control structural and transport properties of oxygen-deficient perovskite SrFeOy (2.5 ≦ y ≦ 3) (SFO) epitaxial films, we employed electric-field-effect transistor structures in which the proton-conducting solid electrolyte Nafion is used as a gate insulator. When a positive gate voltage (VGS) is applied and protons are injected toward the film channel layer, the SFO films are electrochemically reduced, leading to increases in the channel resistance. On the other hand, when a negative VGS is applied and protons are removed, the SFO films are oxidized, and as a result, the channel resistances decrease. In addition, we found that the electrochemically reduced SFO films accommodate protons, forming the proton-containing oxide HxSrFeO2.5 whose proton concentration is determined by elastic recoil detection analysis to be x ∼ 0.11. Our results indicate the usefulness of the proton-conducting solid electrolyte for electrochemically controlling transition metal oxides and for exploring proton-containing oxides. [ABSTRACT FROM AUTHOR]

We fabricated SrRuO3/BaTiO3/GdScO3 heterostructures in which the BaTiO3 layer is one unit cell thick by pulsed laser deposition and elucidated how the BaTiO3 layer influences structural and magneto-transport properties of the SrRuO3 layer through octahedral connections across the heterointerface. Our X-ray-diffraction-based structural characterizations show that while an epitaxial SrRuO3 layer grown directly on a GdScO3 substrate is in the monoclinic phase with RuO3 octahedral tilts, a one-unit-cell-thick BaTiO3 layer inserted between SrRuO3 and GdScO3 stabilizes the tetragonal SrRuO3 layer with largely reduced RuO3 tilts. Our high-angle annular dark-field and annular bright-field scanning transmission electron microscopy observations provide an atomic-level view of the octahedral connections across the heterostructure and reveal that the BaTiO3 layer only one unit cell thick is thick enough to stabilize the RuO3-TiO3 octahedral connections with negligible in-plane oxygen atomic displacements. This results in no octahedral tilts propagating into the SrRuO3 layer and leads to the formation of a tetragonal SrRuO3 layer. The magneto-transport property characterizations also reveal a strong impact of the octahedral connections modified by the inserted BaTiO3 layer on the spin-orbit interaction of the SrRuO3 layer. The SrRuO3 layer on BaTiO3/ GdScO3 has in-plane magnetic anisotropy. This is in contrast to the magnetic anisotropy of the monoclinic SrRuO3 films on the GdScO3 substrate, in which the easy axis is ∼45° to the film surface normal. Our results demonstrate that the one-unit-cell-thick layer of BaTiO3 can control and manipulate the interfacial octahedral connection closely linked to the structure-property relationship of heterostructures. [ABSTRACT FROM AUTHOR]

We fabricated electric double-layer transistors with perovskite nickelate LaNiO3 epitaxial films as a channel and an ionic liquid as a gate insulator and investigated the channel's transport behavior at negative gate bias voltages. We found that when the negative VG is low enough, the channel resistance undergoes reversible changes due to electrostatic carrier accumulation. On the other hand, with increasing VG, electrochemical decomposition of the channels due to the VG-induced instability of the unusually high Ni valence state [Ni(3+δ)+] occurs and the channels are etched, which is seen as an irreversible increase in the channel resistance. We also show that channel layers electrochemically etched to a few nanometers thick exhibit metallic transport behavior and the electrostatic carrier accumulation in the etched metallic channels results in 30% reductions in the channel resistance at 220 K, which are about twice as large as those seen for the ultra-thin insulating film channels. These observations indicate that surface defects and dangling bonds in the electrochemically etched channel layers differ from those in ultrathin films. Our results highlight that the electrochemical decomposition and etching in electric double-layer transistors is a unique approach for fabricating ultrathin oxide films and exploring electric field-induced effects on their functional properties. [ABSTRACT FROM AUTHOR]

Anisotropic in-plane lattice relaxation behavior of brownmillerite SrFeO2.5 epitaxial thin films grown on (110) DyScO3 substrates was investigated. The in-plane lattices in the films less than 50 nm thick are fixed by the substrate lattice, whereas partial in-plane lattice relaxation along the [010] direction occurs in a 50 nm thick film. When the thickness reaches 98 nm, the film eventually exhibits lattice relaxation in both the [010] and the [10-1] in-plane directions. In the bottom region of the partially relaxed film, a dislocation, at which additional Fe atoms are seen, leads to formations of the stacking faults. In the surface region of the film, the complicated lattice defects propagated from the bottom result in the partial in-plane lattice relaxation associated with the disordered arrangements of the FeO4 tetrahedra and the FeO6 octahedra in the surface region. The preferential generation of the dislocations in the (10-1) plane can be explained by taking into account the anisotropic thermal expansion of SrFeO2.5, which results in the increase in the lattice mismatch between the film and the substrate only along the [010] direction in the cooling process after the film deposition. [ABSTRACT FROM AUTHOR]

Spin polarization and magnetic anisotropy are key properties that determine the performance of magnetic tunnel junctions (MTJs), which are utilized in various spintronic devices. Although materials that have both high spin polarization and sufficient perpendicular magnetic anisotropy are desirable for further developments of MTJs, such materials are rare because electronic structures necessary for achieving these two properties are distinct. Here, we experimentally show the inverse spinel ferrimagnet NiCo2O4 (NCO), whose band structure is theoretically predicted to be half-metallic, has both high spin polarization and perpendicular magnetic anisotropy. Perpendicular MTJs with NCO magnetic electrodes exhibit magnetoresistance up to 230%, indicating that the spin polarization of perpendicularly magnetized NCO is as high as −73%. Our experimental results demonstrate the potential of NCO as a half-metal with perpendicular magnetic anisotropy, which will lead to new paradigms for designing and developing all-oxide spintronic devices. [ABSTRACT FROM AUTHOR]

Detailed structural investigations on the substitution-induced structural phase transition from the rhombohedral phase to an orthorhombic phase in (Bi,RE)FeO3 epitaxial thin films (RE = La, Sm, and Dy) grown on (100) SrTiO3 substrates are presented. X ray diffraction reveals that the unit cell dimensions of the orthorhombic phase are strongly dependent on the type of the RE dopant. For RE = La3+ ion, which has an ionic size comparable to the Bi3+ ion, the unit cell is found to be a0 × a0 × 2a0, where a0 is the pseudo-cubic lattice parameter. This is in contrast with the [Square_Root]2a0 × [Square_Root]2a0 × 2a0 unit cell for the case of smaller ionic radius RE (= Sm and Dy) elements. While clear double-hysteresis loops in the polarization versus electric-field curves due to field-induced transitions are observed for smaller ionic radius RE (= Sm and Dy), no signature of the double hysteresis loops is observed for the RE = La case across the structural boundary. We have also performed systematic tracking of the structural phases as functions of the RE composition and temperature, based on which we propose a phase diagram. This work reveals that the ionic size of the RE element plays a critical role in the evolution of the structural and functional properties of RE-substituted BiFeO3 thin film materials systems. [ABSTRACT FROM AUTHOR]

We investigated the thermopower and anomalous Nernst effect in compressively and tensilely strained SrRuO3 films, revealing the influence of the epitaxial strain on the thermoelectric properties. The compressively strained film has a lower Seebeck coefficient than the tensilely strained film. Furthermore, both the sign and the magnitude of the anomalous Nernst effect are found to be strain dependent. For the compressively strained film, the anomalous Nernst coefficient is positive and is as small as 0.03 μV/K. For the tensilely strained film, on the other hand, the coefficient is negative and its maximum absolute magnitude is as large as 0.13 μV/K. Our results highlight the strong influence of epitaxial strain on electronic structures at the EF and their Berry curvature in SrRuO3, resulting in strain-dependent variations in its thermoelectric properties. [ABSTRACT FROM AUTHOR]

A variety of functional properties in transition metal oxides are often underpinned by oxygen vacancies. While the oxygen vacancy concentration and arrangements are well-known to have strong influence on the physical properties of oxides, the oxygen dynamics in oxides—including oxygen ion incorporation and movements during redox reactions—remain elusive. Performing conductive AFM studies of epitaxial thin films of oxygen-deficient SrFeO2.5 treated by air-annealing at various temperatures, we observe oxidation-induced enhancement of local electronic conduction on the higher terraces near the outer step edges at which oxygen ions are preferably incorporated and diffuse into the films. We also show that the local conduction can be reversibly controlled by electric-field-induced redox reactions at room temperature. These results highlight the importance of the nanoscale oxygen dynamics in redox reactions in SrFeO2.5 films. [ABSTRACT FROM AUTHOR]

Phenomena giving rise to voltages transverse to electric currents, such as anomalous and topological Hall effects, have been at the heart of modern condensed matter physics. Here, we show that epitaxial thin films of the itinerant ferromagnetic oxide SrRuO3 exhibit anomalous transverse resistivity associated with magnetization reversal, which is reminiscent of the emergence of the topological Hall effect. The behavior of the anomalous transverse resistivity of SrRuO3 films is found to depend on Ru vacancies. The anomalous peaking behavior in the transverse resistivity is enhanced when the film is thin enough that Ru vacancies significantly influence the magneto‐transport properties. Furthermore, films with fewer Ru vacancies exhibit no anomaly in transverse resistivity. Our observations imply that the Ru vacancies significantly influence the transverse resistivity in SrRuO3 and that defect‐induced changes in electronic structure are a plausible origin for the emergence of the anomalous peaking behavior in the transverse resistivity. [ABSTRACT FROM AUTHOR]

Controlling structural distortions that are closely related to functional properties in transition-metal oxides is a key not only to exploring novel phenomena but also to developing novel oxide-based electronic devices. In this review article, we overview investigations revealing that oxygen displacement at the heterointerface is a key parameter characterizing structure–property relationships of heterostructures. We further demonstrate that the interface engineering of the oxygen displacement is useful to control structural and electronic properties of strained oxides. [ABSTRACT FROM AUTHOR]

Structural distortions in the oxygen octahedral network in transition-metal oxides play crucial roles in yielding a broad spectrum of functional properties, and precise control of such distortions is a key for developing future oxide-based electronics. Here, it is shown that the displacement of apical oxygen atom shared between the octahedra at the heterointerface is a determining parameter for these distortions and consequently for control of structural and electronic phases of a strained oxide film. The present analysis by complementary annular dark- and bright-field imaging in aberration-corrected scanning transmission electron microscopy reveals that structural phase differences in strained monoclinic and tetragonal SrRuO3 films grown on GdScO3 substrates result from relaxation of the octahedral tilt, associated with changes in the in-plane displacement of the apical oxygen atom at the heterointerface. It is further demonstrated that octahedral distortions and magnetrotransport properties of the SrRuO3 films can be controlled by interface engineering of the oxygen displacement. This provides a further degree of freedom for manipulating structural and electronic properties in strained films, allowing the design of novel oxide-based heterostructures. [ABSTRACT FROM AUTHOR]

A clearcorrelation between the A-site cation size and the octahedraltilt propagation from the substrates into the ATiO3(A= Ba2+, Sr2+, Sr2+0.7Ca2+0.3, and Sr2+0.5Ca2+0.5) epitaxial thin films was found from the observationsof ATiO3/GdScO3heterostructures using high-resolutionannular bright-field scanning transmission electron microscopy. Thein-plane oxygen displacements at the interface increase with decreasingthe A-site cation size and facilitate the TiO6octahedraltilt propagation across the interface. The results highlight the significanceof the A-site cation size as a controlling factor for structural distortionsat oxide-based heterointerfaces. [ABSTRACT FROM AUTHOR]

We investigated the transient behavior of Pt/Nb-doped SrTiO3 Schottky junctions that exhibit rectifying and hysteric I-V characteristics. We found that regardless of the junction resistance state, the junction under the bias shows the relaxation behavior over 104 s while the behavior is strongly dependent on the junction resistance state. Detailed investigation of the time dependence of the current and the capacitance of the junctions indicates that the junctions have the inhomogeneous Schottky barrier heights and depletion layer widths while the mean junction profile remains unchanged regardless of the junction resistance state. Given the experimental results, we attribute the observed transient behavior to time-dependent changes in the population of electrons trapped in the local conduction regions under the bias, which play an important role in determining the resistance state of Pt/Nb-doped SrTiO3 junction. [ABSTRACT FROM AUTHOR]

Thickness-dependent structure-property relationships in strained SrRuO3 thin films on GdScO3 (GSO) substrates are reported. The film is found to have epitaxially stabilized crystal structures that vary with the film thickness. Below 16 nm, the √2 apc × √2 apc × 2 apc monoclinic structure is stabilized while above 16 nm the film has the apc × 2 apc × apc tetragonal structure. The thickness-dependent structural changes are ascribed to the substrate-induced modification in the RuO6 octahedral rotation pattern, which highlights the significance of the octahedral rotations for the epitaxial strain accommodation in the coherently-grown films. Close relationships between the structural and physical properties of the films are also found. The monoclinic film has the uniaxial magnetic easy axis 45° away from the [110]GSO direction while the tetragonal film has the one that lies along the in-plane [1-10]GSO direction. The results demonstrate that the octahedral rotations in the strained perovskite oxide thin films are a key factor for determining their structure phases and physical properties. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated the electrical properties of junctions composed of Pt and Nb-doped SrTiO3 single crystals. The fabricated junction shows rectifying and hysteric current–voltage characteristics with high and low resistance states. The current is less dependent on the top electrode area regardless of the resistance state, while the junction capacitance exhibits a linear relationship with the area in both resistance states. The current also shows temporal changes depending on a polarity of applied voltages. The observed behaviors can be understood by considering an existence of conducting channels, along which the current flows dominantly through the capturing and releasing processes of electrons. [Copyright &y& Elsevier]

We have systematically investigated structural and ferroelectric properties of A- and B-site co-doped BiFeO3 thin films using the composition spread technique. X-ray diffraction and polarization hysteresis loop measurements reveal that the co-doped (Bi,Sm)(Fe,Sc)O3 exhibits the structural transition from the rhombohedral to an orthorhombic structural phase which is accompanied by a double-hysteresis behavior in the polarization hysteresis loop. We find that the phase transition takes place at Sm ∼14% independent of the Sc composition. This clearly indicates the significance of the A-site dopant on structural and ferroelectric properties in BiFeO3. [ABSTRACT FROM AUTHOR]

Oxide-based electronic devices are expected to have fascinating properties, unlike those made from conventional semiconductors. SrTiO3 (STO) is a key material for this new field of electronics. Here we report on blue-light emission at room temperature from Ar+-irradiated, metallic STO. The irradiation introduces oxygen deficiencies to a depth of ∼20 nm from the crystal surface. These deficiencies generate conduction carriers and stabilize a hole level in a self-trapped state. We propose a model by which the doped conduction electrons and the in-gap state produce a radiative process that results in blue-light emission. The emitting region can be patterned into any size and shape with conventional microscopic fabrication techniques. [ABSTRACT FROM AUTHOR]

Abstract: We have fabricated heterojunction structures comprising p-type high-T c superconductor (YBCO) and n-type La-doped SrTiO3 (La-STO). (001) and (110) oriented-YBCO thin films were prepared on the (001) and (110)-oriented La-STO substrates, respectively, with the pulsed laser deposition technique. X-ray diffraction measurements confirm that the (001) and (110) YBCO thin films are epitaxially grown on the substrates. The fabricated junctions with both orientations show rectifying I–V characteristic, but their behavior are rather different depending on the orientation. The threshold voltages in the forward bias region increase with decreasing temperature. [Copyright &y& Elsevier]

Electrochemical protonation provides ways to control physical properties and even explore unprecedented phases of solid‐state materials. While how proton accumulation changes materials’ properties is investigated, how protonation of solids can be controlled and promoted remains an enigmatic puzzle. In the work reported here, the influence of electrochemical proton injection duration (tVg) is investigated on the protonation of SrCoO2.5 (SCO) films in electric‐field‐effect transistor structures with gate layers of the proton‐conducting electrolyte Nafion. The proton concentration accumulated in SCO films varies depending on the duration of the proton injection. When protons are injected in a relatively short tVg (≤ 600 s), the hydrogen concentration accumulated in SCO film increases with increasing tVg, reaching the maximum proton concentration of ≈1.9 per formula unit of SCO for the tVg = 600 s case. On the other hand, when tVg is longer than 900 s, the proton concentration decreases with tVg, implying the occurrence of counterreactions that extract protons from protonated SCO and oxidize the channel. These observations indicate that protons accumulated at the Nafion/SCO interface play a role in the protonation of SCO films and that suppressing the interfacial proton accumulation is the key to maximizing the proton concentration accumulated in SCO films. [ABSTRACT FROM AUTHOR]

We report on our characterization of the structural, electrical, and magnetic properties of tetragonal SrRuO3 (SRO) thin films stabilized under both compressive and tensile strain. These tetragonal films consisting of the deformed RuO6 octahedra without rotations were coherently grown on (110)ortho NdGaO3 and (110)ortho GdScO3 substrates, which provide compressive (-1.7%) and tensile (+1.0%) strains, respectively. The ferromagnetic transition temperature TC for the compressively strained film is found to be as high as 155 K, while TC of the film under tensile strain is only 100 K. The longitudinal resistivity ρxx of the compressively strained films is lower than that of the films under the tensile strain. This is attributed to the enhanced mobility for the compressive-strain case. The magnetic anisotropy also exhibits strong dependence on the substrate-induced epitaxial strain. The film under the compressive strain has the uniaxial magnetic easy axis along the out-of-plane direction, while the easy axis of the film under the tensile strain lies along the in-plane direction parallel to the [1-10]GSO one. The results demonstrate that the electrical and magnetic properties of the tetragonal SRO thin films are closely related to the RuO6 octahedral deformations due to the substrate-induced strain. [ABSTRACT FROM AUTHOR]

We investigated effects of the laser fluence on structural and ferroelectric properties in BaTiO3 epitaxial thin films grown by pulsed laser deposition. We find that the low laser fluence causes the cation non-stoichiometry in the films. X-ray diffraction and ferroelectric hysteresis loop measurements reveal the strong impacts of the fluence-dependent cation non-stoichiometry on the structural and ferroelectric properties of the films. The ferroelectricity is observed for the films grown with the fluence larger than 1.3 J/cm2, where the cation ratio is kept close to stoichiometric. These results demonstrate that the cation stoichiometry controlled with the laser fluence plays an important role in determining the structural and ferroelectric properties in the BaTiO3 films. [ABSTRACT FROM AUTHOR]

Structure-electromechanical property correlations in rare-earth (RE)-substituted (001) BiFeO3 (BFO) epitaxial thin films have been investigated. Quantitative piezoelectric coefficient (d33) and dielectric constant ([variant_greek_epsilon]33) measurements, in conjunction with selected area electron diffraction, reveal that the enhancement in d33 and [variant_greek_epsilon]33 at the morphotropic phase boundary (MPB) of the RE-substituted films (RE=Dy3+, Gd3+, and Sm3+) is correlated with the presence of a competing intermediate antipolar phase with the rhombohedral ferroelectric and nonpolar orthorhombic phase. This leads to a complex nanoscale phase coexistence at the MPB. Extending the studies to RE=La3+ case, we find the nanoscale phase coexistence to be less pronounced. This explains the lack of increase in d33 for the La3+-substituted BFO films, in contrast to the Dy3+, Gd3+, and Sm3+-substituted films. [ABSTRACT FROM AUTHOR]

We performed structural investigations of epitaxially grown SrRuO3 films with geometric shapes of one-dimensional stripes and a two-dimensional layer, focusing on how the geometric shapes affect the structural transition behavior from the high-temperature pseudo-cubic phase to the low-temperature orthorhombic one. From the temperature dependence of the out-of-plane lattice parameter of the films, we found that the structural transition in the stripe-shape film occurs in a narrower temperature range as compared to that in the layer-shape film. Detailed reciprocal space mappings reveal that in the stripe-shape film, crystallographic twins are formed in the orthorhombic phase due to the strain relaxation along the [1-10]ortho_SRO direction and as a consequence the transition occurs in the narrower temperature range. In contrast, the layer-shape film is fully strained and maintains a single crystallographic domain across the transition. The results indicate that the strain effect on the structural transition behavior is strongly dependent on the geometric shapes of the films. [ABSTRACT FROM AUTHOR]

A correction to the article "Nanoscale oxygen ion dynamics in SrFeO2.5+δ epitaxial thin films" which was published in issue #113 of the journal "Applied Physics Letters" is presented.

Oxygen coordination of transition metals is a key for functional properties of transition-metal oxides, because hybridization of transition-metal d and oxygen p orbitals determines correlations between charges, spins and lattices. Strain often modifies the oxygen coordination environment and affects such correlations in the oxides, resulting in the emergence of unusual properties and, in some cases, fascinating behaviors. While these strain effects have been studied in many of the fully-oxygenated oxides, such as ABO3 perovskites, those in oxygen-deficient oxides consisting of various oxygen coordination environments like tetrahedra and pyramids as well as octahedra remain unexplored. Here we report on the discovery of a strain-induced significant increase, by 550 K, in the metal-insulator transition temperature of an oxygen-deficient Fe oxide epitaxial thin film. The observed transition at 620 K is ascribed to charge disproportionation of Fe3.66+ into Fe4+ and Fe3+, associated with oxygen-vacancy ordering. The significant increase in the metal-insulator transition temperature, from 70 K in the bulk material, demonstrates that epitaxial growth of oxygen-deficient oxides under substrate-induced strain is a promising route for exploring novel functionality. [ABSTRACT FROM AUTHOR]

Thiothrix nivea is a filamentous sulfur-oxidizing bacterium common in activated sludge and its filament is covered with a polysaccharide layer called sheath. In this study, we found that T. nivea aggregates under acidic conditions. A hexagonal lattice pattern, a typical morphological feature of proteinaceous S-layers, was newly observed on the surface of the sheath by transmission electron microscopy. The pattern and the acid-dependent aggregation were not observed in T. fructosivorans, a relative sheath-forming bacterium of T. nivea. The putative S-layer of T. nivea was detached by washing with unbuffered tris(hydroxymethyl)aminomethane base (Tris) solution and a protein of 160 kDa was detected by electrophoresis. Based on partial amino acid sequences of the protein, its structural gene was identified. The gene encodes an acidic protein which has a putative secretion signal and a Ca2+-binding domain. The protein was solubilized with urea followed by dialysis in the presence of calcium. A hexagonal lattice pattern was observed in the aggregates formed during dialysis, revealing that the protein is responsible for S-layer formation. Biosorption ability of copper, zinc, and cadmium onto the T. nivea filament decreased upon pretreatment with Tris, demonstrating that the S-layer was involved in metal adsorption. Moreover, aggregation of Escherichia coli was promoted by acidification in the presence of the S-layer protein, suggesting that the protein is potentially applicable as an acid-driven flocculant for other bacteria. [ABSTRACT FROM AUTHOR]

On page 5177, D. Kan, H. Kurata, and co‐workers discuss high‐resolution ABF‐STEM observations which reveal that picometer‐order displacements of the oxygen atoms at the heterointerfaces between transition‐metal oxides have a close correlation with structural distortions in the thin film heterostructures. The oxygen displacement can also be modified by inserting a unit‐cell thick oxide layer, demonstrating that the manipulation of the oxygen displacement at the interface is a good way to control the structural distortions that determine functional properties of oxide thin films. [ABSTRACT FROM AUTHOR]

Oxygen incorporation into the title compounds is investigated by XRD and thermogravimetry. [ABSTRACT FROM AUTHOR]

Spin current, converted from charge current via spin Hall or Rashba effects, can transfer its angular momentum to local moments in a ferromagnetic layer. In this regard, the high charge‐to‐spin conversion efficiency is required for magnetization manipulation for developing future memory or logic devices including magnetic random‐access memory. Here, the bulk Rashba‐type charge‐to‐spin conversion is demonstrated in an artificial superlattice without centrosymmetry. The charge‐to‐spin conversion in [Pt/Co/W] superlattice with sub‐nm scale thickness shows strong W thickness dependence. When the W thickness becomes 0.6 nm, the observed field‐like torque efficiency is about 0.6, which is an order larger than other metallic heterostructures. First‐principles calculation suggests that such large field‐like torque arises from bulk‐type Rashba effect due to the vertically broken inversion symmetry inherent from W layers. The result implies that the spin splitting in a band of such an ABC‐type artificial SL can be an additional degree of freedom for the large charge‐to‐spin conversion. [ABSTRACT FROM AUTHOR]

Using a time-resolved magneto-optical Kerr effect microscope, we observed ultrafast demagnetization of inverse-spinel-type ferrimagnet NiCo2O4 (NCO) epitaxial thin films with perpendicular magnetic anisotropy. This microscope uses a pump-probe method, where the sample is pumped at 1030 nm, and magnetic domain images are acquired via magneto-optical Kerr effect microscopy at 515 nm (the second harmonic). We observed the dynamics of the magnetic domain of the NCO thin film via laser irradiation and obtained a demagnetization time constant of approximately 0.4 ps. This time constant was significantly smaller than the large time constants reported for other half-metallic oxides. This timescale of ∼0.4 ps agrees with the spin polarization of ∼0.7 determined by tunnel magnetoresistance [Shen et al., Appl. Phys. Lett. 117, 042408 (2020)]. [ABSTRACT FROM AUTHOR]

Sphaerotilus natans is a filamentous sheath-forming bacterium commonly found in activated sludge. Its sheath is assembled from a thiolic glycoconjugate called thiopeptidoglycan. S. montanus ATCC-BAA-2725 is a sheath-forming member of stream biofilms, and its sheath is morphologically similar to that of S. natans. However, it exhibits heat susceptibility, which distinguishes it from the S. natans sheath. In this study, chemical composition and solid-state NMR analyses suggest that the S. montanus sheath is free of cysteine, indicating that disulfide linkage is not mandatory for sheath formation. The S. montanus sheath was successfully solubilized by N -acetylation, allowing solution-state NMR analysis to determine the sugar sequence. The sheath was susceptible to thiopeptidoglycan lyase prepared from the thiopeptidoglycan-assimilating bacterium, Paenibacillus koleovorans. The reducing ends of the enzymatic digests were labeled with 4-aminobenzoic acid ethyl ester, followed by HPLC. Two derivatives were detected, and their structures were determined. We found that the sheath has no peptides and is assembled as follows: [→4)-β- d -GlcA-(1→4)-β- d -Glc-(1→3)-β- d -GalNAc-(1→4)-α- d -GalNAc-(1→4)-α- d -GalN-(1→] n (β- d -Glc and α- d -GalNAc are stoichiometrically and substoichiometrically 3- O -acetylated, respectively). Thiopeptidoglycan lyase was thus confirmed to cleave the 1,4 linkage between α- d -GalN and β- d -GlcA, regardless of the peptide moiety. Furthermore, vital fluorescent staining of the sheath demonstrated that elongation takes place at the tips, as with the S. natans sheath. [ABSTRACT FROM AUTHOR]

Caloric effects of solids can provide us with innovative refrigeration systems more efficient and environment-friendly than the widely-used conventional vapor-compression cooling systems. Exploring novel caloric materials is challenging but critically important in developing future technologies. Here we discovered that the quadruple perovskite structure ferrimagnet BiCu3Cr4O12 shows large multiple caloric effects at the first-order charge transition occurring around 190 K. Large latent heat and the corresponding isothermal entropy change, 28.2 J K−1 kg−1, can be utilized by applying both magnetic fields (a magnetocaloric effect) and pressure (a barocaloric effect). Adiabatic temperature changes reach 3.9 K for the 50 kOe magnetic field and 4.8 K for the 4.9 kbar pressure, and thus highly efficient thermal controls are achieved in multiple ways. [ABSTRACT FROM AUTHOR]

Materials which show novel thermal properties can be used to make highly efficient and environmentally friendly energy systems for thermal energy storage and refrigeration through caloric effects. An A‐site‐ordered quadruple perovskite‐structure oxide, NdCu3Fe4O12, is found to release significant latent heat, 25.5 kJ kg−1 (157 J cc−1), at the intersite‐charge‐transfer transition temperature near room temperature. The transition is first‐order and accompanied by an unusual magnetic ordering and a large negative‐thermal‐expansion‐like volume change, and thus, it causes a large entropy change (84.2 J K−1 kg−1). The observed entropy change is comparable to the largest changes reported in inorganic solid materials, and more importantly, it is utilized through a colossal barocaloric effect. The adiabatic temperature change by applying 5.1 kbar pressure is estimated to reach 13.7 K, which means efficient refrigeration can be realized through this effect. [ABSTRACT FROM AUTHOR]

Epitaxial thin films of Bi2NiMnO6 were synthesized on SrTiO3 substrates by pulsed laser deposition. The resulting film had the rock-salt-type arrangement of Ni2+ and Mn4+ ions in a double-perovskite unit cell. The films clearly showed multiferroic properties, both ferromagnetic behavior with a Curie temperature of about 100 K and ferroelectric behavior with a saturated polarization of about 5 μC/cm2. [ABSTRACT FROM AUTHOR]

Thiothrix nivea is a filamentous sulfur-oxidizing bacterium commonly found in activated sludge. The filament of this bacterium is covered with a sheath. The sheath is an assemblage of macromolecular glucosaminoglucan (GG), [4)-β- d -GlcN-(1 → 4)-β- d -Glc-(1 → ] n , modified with an unidentified deoxy-sugar at position 3 of Glc. GG was obtained by dialysis after the partial hydrolysis of the sheath. The GG hydrogel was prepared by drying a GG solution. Then, the hydrogel was N -acetylated to prepare a stable hydrogel of N -acetylglucosaminoglucan (NGG), [4)-β- d -GlcNAc-(1 → 4)-β- d -Glc-(1 → ] n . The NGG hydrogel was stable in phosphate buffer but was disrupted by lysozyme addition, suggesting that NGG is susceptible to lysozyme degradation and has potential for medical use. The GG solution was N -acetylated to prepare a NGG suspension to confirm enzymatic degradation. The turbidity of the NGG suspension was decreased by lysozyme addition. Sugars released in the reaction mixture were derivatized with 4-aminobenzoic acid ethyl ester (ABEE) followed by HPLC analysis. Two major derivatives were detected, and their concentration was increased in reverse proportion to the turbidity of the reaction mixture. The derivatives were identified as GlcNAc-Glc-GlcNAc-Glc-ABEE and GlcNAc-Glc-ABEE by mass spectrometry. Consequently, NGG was found to be degraded by lysozyme via a mechanism similar to that of chitin degradation. [ABSTRACT FROM AUTHOR]

Colossal Barocaloric Effect: Colossal Barocaloric Effect by Large Latent Heat Produced by First-Order Intersite-Charge-Transfer Transition (Adv. Funct. Keywords: barocaloric effect; charge transition; large latent heat; perovskite oxides; thermal property EN barocaloric effect charge transition large latent heat perovskite oxides thermal property 1 1 1 06/21/21 20210616 NES 210616 In article number 2009476, Yuichi Shimakawa and co-workers present an A-site-ordered quadruple perovskite NdCu SB 3 sb Fe SB 4 sb O SB 12 sb that releases significant latent heat at the intersite-charge-transfer transition temperature near room temperature. Barocaloric effect, charge transition, large latent heat, perovskite oxides, thermal property. [Extracted from the article]

Crystal structures and ionic conductivity of antiperovskites Li 2 OHX (X ​= ​Cl, Br), which are potential solid electrolyte materials for all-solid-state Li-ion batteries, were investigated. Li 2 OHCl showed a Pmc 2 1 orthorhombic structure at room temperature and changed to a P m 3 ‾ m cubic one between 27 and 37 ​°C. Li 2 OHBr, on the other hand, crystallized in a P m 3 ‾ m cubic structure and showed no phase transition in the measured temperature range. The cubic phases of both compounds showed dominant high Li+-ion conductivity, while the orthorhombic phase of Li 2 OHCl exhibited reduced ionic conductivity. The Li+-ion order in the orthorhombic Li 2 OHCl makes the crystal structure highly anisotropic and two dimensional, which disturbs the hopping of the Li+ ions. Ionic conductivity for Li 2 OHCl and Li 2 OHBr. The cubic phases show dominant high Li+-ion conductivity, while the orthorhombic phase of Li 2 OHCl exhibited reduced ionic conductivity. Image 1 [ABSTRACT FROM AUTHOR]