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Numerous hybrid improper ferroelectrics have been discovered in bulk oxides with layered perovskite structures. In contrast, the competition between the interlayer rumpling and oxygen octahedral rotation suppresses the ferroelectricity in layered perovskite material with trivalent cation at the B-site. In the present work, single-phase dense La2Sr(Sc1−xFex)2O7 ceramics with double-layered Ruddlesden–Popper structures have been prepared, and room-temperature ferroelectricity is discovered in the ceramics with x ≤ 0.10. The ferroelectric polarization and coercive field decrease with increasing content of Fe3+ cations, consistent with the decline of oxygen octahedral rotation and tilting angles. Although the linear relationship between the Curie temperature and the tolerance factor for La2Sr(Sc1−xFex)2O7 ceramics is established, the line is far away from that for A2+3B4+2O7 ceramics due to the large interlayer rumpling in the present ceramics. Although no single-phase multiferroic has been discovered in this work, an effective way to introduce magnetism into hybrid improper ferroelectric is provided. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junction (MTJ) is one of the cornerstones of modern information technologies. Bringing MTJ's operation beyond the conventional binary regime, enabled by tunneling magnetoresistance (TMR) effect, is highly promising for prospective memory technologies and neuromorphic hardware development. In this paper, we demonstrate multilevel magnetoresistance states in an all-perovskite-oxide La0.7Sr0.3MnO3 (LSMO)/BaTiO3/LSMO heterostructure grown on MgO substrates. Unlike traditional TMR, we observe four distinct regions of increased magnetoresistance, which result in three magnetic field-induced resistance states in total. We show that the observed phenomenon arises from the low-field magnetoresistance effect, which occurs in the two epitaxial LSMO layers, independently and at different values of the magnetic field. The effect is well simulated by a model based on the presence of structural defects and non-uniform deformations in the LSMO layers, induced by the large lattice mismatch of the LSMO with the MgO substrate. We believe that our findings contribute to the understanding of complex magnetoresistance effects in MTJs and can be taken into consideration for the design of multi-bit memory cells or neuromorphic devices. [ABSTRACT FROM AUTHOR]

Polar discontinuities occur in oxide heterostructures due to varying net charges in the sub-unit cell layers. These polar discontinuities lead to structural reconstruction and often create diverse functionalities. This work constructs polar discontinuous in La0.67Sr0.33MnO3/SrCuO2 (LSMO/SCO) heterostructures on a (001)-orientated SrTiO3 (STO) substrate under different configurations. By changing the growth order of LSMO and SCO, we found two different compensating mechanisms for polar discontinuity. When LSMO is grown on SCO, interfacial polarity discontinuities result in the generation of a large number of oxygen vacancies within the LSMO film. Thus, the LSMO magnetism deteriorates. For the SCO/LSMO/SCO trilayer, the SCO capping layer can recover the LSMO magnetism. The scanning transmission electron microscope results show an atomic reconstruction at the SCO-on-LSMO interface and several oxygen vacancies at the SrO sublayer. The interface reconfiguration releases the polar energy, thereby inhibiting the generation of oxygen vacancies and improving the ferromagnetism of the LSMO film. Our work studies the impact of polar discontinuity at the interface, providing insights into the effects of interface polar discontinuities on functional materials. [ABSTRACT FROM AUTHOR]

We report the development of a compact, highly stable, monolithic-cavity, GaInP/AlGaInP-based vertical-external-cavity surface-emitting laser (VECSEL) with electronically tunable emission wavelength centered at 689.4425 nm for neutral strontium (Sr)-based applications. The output power reaches 40 mW (pump-power-limited) with ultra-low frequency and intensity noise performance resulting in a free-running linewidth of 720 Hz, reduced to 390 Hz when frequency locked to a reference cavity and verified via a heterodyne beat note measurement with 2 s averaging time. For shorter averaging times (0.1 ms), the free-running linewidth is as low as 40 Hz. We estimate a Lorentzian, or intrinsic, linewidth of 64 mHz from the frequency noise power spectral density at high frequencies, thus providing further evidence of the ultra-narrow fundamental linewidth of VECSELs. High frequency stability was measured via Allan deviation resulting in 1.05 × 10−12 at 2 s and 2.11 × 10−13 at 7 s averaging times when the 689 nm monolithic cavity VECSEL is free-running and locked, respectively, suitable for neutral Sr-based quantum technologies, such as optical clocks and atom interferometry. [ABSTRACT FROM AUTHOR]

We designed, demonstrated, and characterized a strontium atom source based on fiber-based pulsed laser ablation. By using a commercially available miniature lens system for focusing nanosecond pulsed laser of up to 225 μ J delivered through a multimode fiber of 105 μ m core, we ablate a SrTiO3 target and generate a jet of neutral strontium atoms, though our method can be applied to other transparent ablation targets containing materials under concern. Our device endures 6000 cycles of pulse delivery and irradiation without noticeable damage on the fiber facets and lenses. The generated strontium beam is characterized with a spectroscopic method and is revealed to exhibit the transverse temperature of 800 K and a longitudinal velocity of 2300 m/s, which are typical for a pulsed-laser-ablation-based atom source. The number of atoms generated by a single ablation pulse is estimated to be 2 × 10 5 . Our device provides a compact, cryo-compatible fiber-pigtailed atom source with minimized device footprints and reduced complexity of vacuum systems to further promote development of cold-atom experiments. It may also find interesting applications in atomic and molecular sciences. [ABSTRACT FROM AUTHOR]

To introduce coexistence of several ordering parameters in a material is a key but a very challenging goal in correlated materials, which can bring many novel phenomena and offer unprecedented opportunities for new device functions. Here, we demonstrate a general route to induce nanoscale periodic ferroelastic twins in otherwise weak- or non-ferroelastic perovskite oxides by coherently propagating ferroelastic twins in template materials into atop other films through unique structure coupling at perovskite oxide interfaces. Using the LaCoO3 thin film as a template and deliberately growing La2/3Sr1/3MnO3/LaCoO3 on the NdGaO3 (110) substrate, we were able to realize uniaxially and periodically ordering nanoscale ferroelastic twins in LaCoO3, and more importantly, such ferroelastic domain structure can be coherently transferred into La2/3Sr1/3MnO3. The uniaxial periodic ferroelastic twins in La2/3Sr1/3MnO3 can induce strong magnetic anisotropy which can compete with magneto-crystalline anisotropy, illustrating strong coupling between the ferromagnetism and ferroelasticity in La2/3Sr1/3MnO3. Our results provide a meaningful reference toward desired ferrelasticity for generating multiferrocity and developing novel oxide electronics. [ABSTRACT FROM AUTHOR]

A series of La0.7K0.3−xSrxMnO3 (0.00 ≤ x ≤ 0.3) films were fabricated on LaAlO3 substrates using a sol-gel spin-coating technique. The relationship between electrical transport properties and a microstructure was explained via the Jahn–Teller effect, a phenomenological percolation model, and a double-exchange mechanism. The results revealed the strong impact of K and Sr co-occupying A-sites on the formation of Mn3+/Mn4+ pairs, crystal structure, conductivity, surface morphology, and in-plane and out-of-plane strains. The as-fabricated La0.7K0.25Sr0.05MnO3 films showed a peak temperature coefficient of resistivity of 16.63% K−1 at 298.3 K. [ABSTRACT FROM AUTHOR]

A high-performance energy storage capacitor would not display high energy storage density (Ue) but high energy storage efficiency (η). However, during raising the electric field (E) or temperature (T), the η in dielectric thin films often shows an obvious degradation process. The degradation process is closely related to the change of the charge carrier transport mechanism as a function of E or T. Compared with the electric breakdown strength, the relationship between η and the charge carrier transport mechanisms in the dielectric thin films was less concerning. In this work, by increasing the trigger E and T of the space charge limited current mechanism, the beginning of the η degradation process was delayed into higher E and T. Consequently, a high Ue (∼56.6 J/cm3) and η (∼93.9%) were achieved simultaneously in Ba0.3Sr0.7Zr0.18Ti0.82O3/LaNiO3 heterostructure thin films directly deposited on low-cost conductive silicon wafers. Moreover, the temperature stability was greatly improved. This result would also offer a promising approach to improve the electrical properties of the dielectric oxide thin films in a harsh environment of high temperatures by redistributing oxygen vacancies through the heterostructure interface. [ABSTRACT FROM AUTHOR]

Integrating functional oxide-based nanocomposite thin films on Si wafer is a large step toward their applications in electronics and spintronics. Here, to overcome the large lattice mismatch and potential inter-diffusion between the complex oxides and Si, a set of buffer layers of SrRuO3 (SRO)/TiN have been applied. The La0.7Sr0.3MnO3:BiFeO3 system has been selected to grow on the SRO/TiN buffered Si, and the nanocomposite films exhibit highly textured growth along the c direction for both phases. The microstructure study shows a typical vertically aligned nanocomposite structure of the films, which is similar to the same films on single crystal oxide substrates. Furthermore, magnetic measurements indicate the strong ferromagnetic–antiferromagnetic coupling in the nanocomposite system, which refers to the large exchange bias value HEB of ∼1800 Oe in the L0.5B0.5 sample under out-of-plane magnetic field. This work provides an effective approach for the Si integration of oxide-based nanocomposite thin films. [ABSTRACT FROM AUTHOR]

The heavier alkaline-earth hydrides AeH2 (Ae = Ca, Sr, and Ba) are considered as promising materials for hydrogen energy storage. Pressure-induced structural changes in AeH2 materials could improve hydrogen transport properties and result in a better understanding of the structure-property relationship. In this work, pressure evolution of carrier transport properties of SrH2 was investigated using impedance spectroscopy measurements at room temperature and first-principles calculations. The pressure-induced structure phase transition from a Pnma phase to a P63/mmc phase was accompanied by a transition from pure electronic conduction to mixed ionic-electronic conduction, which was related to the ionic migration barrier energy. In the P63/mmc phase, the H− ionic and electronic resistances of bulk and grain boundaries were distinguished, respectively. The total resistance of SrH2 decreased by about four orders of magnitude after the phase transition. This work provides critical insight into the structure-conduction relationship and the role of grain boundaries in the transport process of alkaline-earth hydrides under high pressure. [ABSTRACT FROM AUTHOR]

A radiation-resistant nuclear battery combining betavoltaic and photovoltaic techniques was demonstrated using Ce-doped Gd3Ga3Al2O12 single-crystal scintillator. The present device comprising 1 mm thick Ce-doped GGAG single-crystal scintillator and Si-based p–i–n diode produced an electric power output of 48 nW with a short-circuit current of 490 nA and an open-circuit voltage of 0.18 V using a 3 mCi 106Ru source. Long-term radiation stability test carried out for more than 4000 h revealed that there was no significant reduction in the output of beta-photovoltaic device (with scintillator), whereas there was 68% reduction in the output power for the betavoltaic device (without scintillator). The electron beam irradiation of 1 mm thick Ce-doped GGAG scintillator up to a dose level of 5 MGy using 10 MeV electron beam indicated a power degradation by 4% suggesting a reasonably long battery life (∼15 years) with 90Sr-90Y source. [ABSTRACT FROM AUTHOR]

Manganites (R1−xAxMnO3, R = rare-earth cation and A = alkali or alkaline earth cation) host an immense number of phases and electronic properties, which can be mainly manipulated through conventional structural control such as metallic cations, oxygen concentration, or misfit strain. However, their practical applications are heavily hindered due to the requirement of rigid synthesis conditions and prolonged treatment time. Herein, a subtle hydrogenation of canonical epitaxial La0.3Sr0.7MnO3 films gives rise to a series of structural transformations ranging from the perovskite to the intermediate state and to the brownmillerite one, accompanied by tunable electronic performances from the antiferromagnetic insulating phase to the weak magnetic insulating one. Moreover, the hydrogenated La0.3Sr0.7MnO3−δ films show an ultra-high magnetic temperature (>400 K). The efficient modulations of the crystalline structure and functionalities of manganite oxides using the facile hydrogenation process enable practical applications of high-temperature magnetic insulators in spintronic devices. [ABSTRACT FROM AUTHOR]

The ferromagnetic metal La2/3Sr1/3MnO3 (LSMO) is an important correlated oxide material for oxide spintronics. However, the existence of a dead layer not only degrades device performance but also hinders the ultimate miniaturization of devices. Intense research has been made to eliminate the dead layer and understand its origin. Here, we have investigated the dead layer of (110)-oriented LSMO films on SrTiO3 (STO) substrates in which there is no polar discontinuity across the interface, in contrast to the (001)-oriented LSMO/STO interface. Our results reveal an 8 unit cell (u.c.) dead layer for (110) LSMO. Angle resolved x-ray photoemission demonstrating Sr segregation at the surface. Additionally, the broken symmetry at LSMO/vacuum interfaces also degrades the transport property. By introducing a capping layer, the film conductivity is enhanced. Finally, an ultrathin limit dead layer of 5 u.c. (=1.36 nm) has been obtained by introducing both the LaMnO3 capping layer and the buffer layer to compensate the excess holes at both LSMO/STO and Vacuum/LSMO interfaces and also to reduce the structural distortion at the top surface of LSMO. Our work paves the way toward eliminating the LSMO dead layer for spintronics application and provides a route to engineer the intriguing physical properties of oxide heterointerfaces. [ABSTRACT FROM AUTHOR]

We report on the artificial manipulation of interfacial magnetism in the superlattices (SLs) of ([La0.7Sr0.3MnO3]30/[BaTiO3]25)n (1 ≤ n ≤ 10) fabricated by pulsed laser deposition. The thicker 30 uc-La0.7Sr0.3MnO3 and 25 uc-BaTiO3 layers are designed as a single period of SLs in order to eliminate the interaction between two adjacent interfaces that could contribute to a polar phase transition and the corresponding magnetism. We use aberration-corrected scanning transmission electron microscopy and electron energy-loss spectroscopy to demonstrate that epitaxial-strain-driven lattice distortion renders the emergence of divalent Mn at the La0.7Sr0.3MnO3/BaTiO3 interfaces. The saturated magnetization decreases and the magnetic easy axis becomes more in-plane inclined as the interfacial strain of the SLs increases. [ABSTRACT FROM AUTHOR]

Photochemically patterned metal nanoparticle Strontium Barium Niobate (SBN) surfaces are shown to exhibit tunable surface wettability which depends on the UV photodeposition time and the type of deposited metal nanoparticle, namely, silver or gold. Taking advantage of plasmonic properties of noble metal nanoparticles, we demonstrate enhanced Raman scattering and fluorescence emission of a probe molecule from the metal nanoparticle SBN surfaces. Further, ferroelectric lithography enables the creation of stable oppositely polarized ferroelectric domains, at the microscale, giving rise to spatially distinct metal particle deposition patterns and corresponding Raman responses. The results clearly demonstrate that metal nanoparticle/SBN surfaces suitable for enhanced chemical sensing can be designed using ferroelectric lithography and could have implications for realization of microfluidic or liquid droplet-based Surface Enhanced Raman Scattering (SERS) sensors. [ABSTRACT FROM AUTHOR]

Laser light with spectral purity and frequency stability is pursued in precision spectroscopy and precision measurements. We propose a scheme to generate millihertz-linewidth laser light with a frequency instability of 10−18 via optical four-wave mixing in alkaline-earth atoms. We show that the linewidth of the mixing laser light is ultimately limited by the natural linewidth of the atomic transition rather than by the linewidth of the input lasers. The frequency stability of the mixing laser light depends largely on the intensity stability of the input lasers. It is possible to generate a millihertz-linewidth laser light with a frequency instability of 10−18 and a power of 10−12 W when the input lasers with a relative intensity instability of 10−4 and a spectral width of 1 Hz interact with strontium (Sr) atoms with a density of 1 × 1011 cm−3. [ABSTRACT FROM AUTHOR]

Different dopants with their specific dopant concentration can be utilized to produce ferroelectric HfO2 thin films. In this work, it is explored for Sr in a comprehensive first-principles study. Density functional calculations reveal structure, formation energy, and total energy of the Sr related defects in HfO2. We found the charge compensated defect with an associated oxygen vacancy SrHfVO to strongly favour the non-ferroelectric, tetragonal P42/mnc phase energetically. In contrast, the uncompensated defect without oxygen vacancy SrHf favours the ferroelectric, orthorhombic Pca21 phase. According to the formation energy, the uncompensated defect can form easily under oxygen rich conditions in the production process. Low oxygen partial pressure existing over the lifetime promotes the loss of oxygen leading to VO, and thus, the destabilization of the ferroelectric, orthorhombic Pca21 phase is accompanied by an increase of the leakage current. This study attempts to fundamentally explain the stabilization of the ferroelectric, orthorhombic Pca21 phase by doping. [ABSTRACT FROM AUTHOR]

Different dopants with their specific dopant concentration can be utilized to produce ferroelectric HfO2 thin films. In this work, it is explored for Sr in a comprehensive first-principles study. Density functional calculations reveal structure, formation energy, and total energy of the Sr related defects in HfO2. We found the charge compensated defect with an associated oxygen vacancy SrHfVO to strongly favour the non-ferroelectric, tetragonal P42/mnc phase energetically. In contrast, the uncompensated defect without oxygen vacancy SrHf favours the ferroelectric, orthorhombic Pca21 phase. According to the formation energy, the uncompensated defect can form easily under oxygen rich conditions in the production process. Low oxygen partial pressure existing over the lifetime promotes the loss of oxygen leading to VO, and thus, the destabilization of the ferroelectric, orthorhombic Pca21 phase is accompanied by an increase of the leakage current. This study attempts to fundamentally explain the stabilization of the ferroelectric, orthorhombic Pca21 phase by doping. [ABSTRACT FROM AUTHOR]

We report that epitaxial Sr2IrO4 thin-films can be selectively grown using pulsed laser deposition (PLD). Due to the competition between the Ruddlesden-Popper phases of strontium iridates (Srn+1IrnO3n+1), conventional PLD methods often result in mixed phases of Sr2IrO4 (n=1), Sr3Ir2O7 (n=2), and SrIrO3 (n=∞). We have discovered that reduced PLD plume dimensions and slow deposition rates are the key for stabilizing pure Sr2IrO4 phase thin-films, identified by realtime in-situ monitoring of their optical spectra. The slow film deposition results in a thermodynamically stable TiO2\\SrO\IrO2\SrO\SrO configuration at an interface rather than TiO2\\SrO\SrO\IrO2\SrO between a TiO2-terminated SrTiO3 substrate and a Sr2IrO4 thin film, which is consistent with other layered oxides grown by molecular beam epitaxy. Our approach provides an effective method for using PLD to achieve pure phase thin-films of layered materials that are susceptible to several energetically competing phases. [ABSTRACT FROM AUTHOR]

We report on the ferromagnetic-like behavior in otherwise diamagnetic BaTiO3 (BTO) thin films upon doping with non-magnetic element Sr having the composition Ba0.4Sr0.6TiO3 (BST). The epitaxial integration of BST (~800 nm) thick films on Si (100) substrate was achieved using MgO (40 nm) and TiN (20 nm) as buffer layers to prepare BST/MgO/TiN/Si (100) heterostructure by pulsed laser deposition. The c-axis oriented and cube-on-cube epitaxial BST is formed on Si (100) as evidenced by the in-plane and out-of-plane X-ray diffraction. All the deposited films are relaxed through domain matching epitaxy paradigm as observed from X-ray diffraction pattern and A1TO3 mode (at 521.27 cm–1) of Raman spectra. As-deposited BST thin films reveal ferromagnetic-like properties, which persist up to 400 K. The magnetization decreases two-fold upon oxygen annealing. In contrast, as-deposited un-doped BTO films show diamagnetism. Electron spin resonance measurements reveal no evidence of external magnetic impurities. XRD and X-ray photoelectron spectroscopy spectra show significant changes influenced by Sr doping in BTO. The ferromagnetic-like behavior in BST could be due to the trapped electron donors from oxygen vacancies resulting from Sr-doping. [ABSTRACT FROM AUTHOR]

In this paper, we report on the active filtering and amplification of a single mode from an optical femtosecond laser comb with mode spacing of 250MHz by optical injection of two external-cavity diode lasers operating in cascade to build a narrow linewidth laser for laser cooling of the strontium atoms in an optical lattice clock. Despite the low injection of individual comb mode of approximately 50 nW, a single comb line at 689 nm could be filtered and amplified to reach as high as 10 mW with 37 dB side mode suppression and a linewidth of 240 Hz. This method could be applied over a broad spectral band to build narrow linewidth lasers for various applications. [ABSTRACT FROM AUTHOR]

The formation of a 1/2 monolayer (ML) of strontium (Sr) on Si(001) represents the most widely used and effective passivation procedure for the epitaxial growth of strontium titanate (SrTiO3) on Si with molecular beam epitaxy (MBE). In the present study, we demonstrate experimentally the possibility of preparing such a buffer layer with the pulsed-laser deposition (PLD) technique. In-situ analysis using reflection high-energy electron diffraction (RHEED) showed surface structure evolution from two-domain (2 × 1) + (1 × 2), exhibited by the bare silicon surface, to a (3 × 2) + (2 × 3) structure at 1/6 ML Sr coverage, which is then replaced by (1 × 2) + (2 × 1) structure at 1/4 ML and maintained up to 1/2 ML coverage. In addition, two different processes for the removal of native silicon dioxide (SiO2) layer were studied: thermal and Sr-induced deoxidation process. Annealing above 1100 °C proved to be the most efficient in terms of carbon contamination. The results highlight the possibilities of using the PLD technique for the synthesis of an epitaxial SrTiO3 layer on Si, needed for the integration of different functional oxides with a Si platform. [ABSTRACT FROM AUTHOR]

We investigated the migration energy and vacancy formation energy of La and Sr ions at a LaAlO3/SrTiO3 heterointerface using first-principles calculations. Our study reveal that the migration energies at the p-type interface are lower than those at the n-type interface, and the formation energies of Sr and La vacancies are relatively high when we assume a reduction atmosphere and insulator conditions. To explain the experimental evidence that intermixing is preferentially taking place at the n-type interface, considering the Fermi energy is critical. We find that the presence of electron carriers plays an important role in the intermixing behaviors at the LaAlO3/SrTiO3 heterointerface. [ABSTRACT FROM AUTHOR]

The electric field effect on ferromagnetism offers a new dimension in the recent advancement of spintronics. We report on the gate control of transport properties in thin films of oxide-based ferromagnetic metal, SrRuO3. An electric double layer transistor configuration was utilized with an ionic liquid dielectric to apply a strong electric field on a SrRuO3 thin film of 5 monolayers in thickness. The application of gate voltage induced a clear electroresistance effect, despite a considerably-large initial carrier density of the order of 1022cm-3. Furthermore, we found that the gate modulation of the anomalous Hall conductivity rx y, which was as large as ~±40% at low temperatures, was about three times larger than that of the longitudinal conductivity σxx. The variation of σxy is characterized by the power-law scaling relation with σx x, which is widely observed in a bad metal regime of the charge transport. [ABSTRACT FROM AUTHOR]

The electric field effect on ferromagnetism offers a new dimension in the recent advancement of spintronics. We report on the gate control of transport properties in thin films of oxide-based ferromagnetic metal, SrRuO3. An electric double layer transistor configuration was utilized with an ionic liquid dielectric to apply a strong electric field on a SrRuO3 thin film of 5 monolayers in thickness. The application of gate voltage induced a clear electroresistance effect, despite a considerably-large initial carrier density of the order of 1022cm-3. Furthermore, we found that the gate modulation of the anomalous Hall conductivity rx y, which was as large as ~±40% at low temperatures, was about three times larger than that of the longitudinal conductivity σxx. The variation of σxy is characterized by the power-law scaling relation with σx x, which is widely observed in a bad metal regime of the charge transport. [ABSTRACT FROM AUTHOR]

122 type pnictide superconductors are of particular interest for high-field applications because of their large upper critical fields Hc2 (> 100 T) and low anisotropy γ (<2). Successful magnet applications require fabrication of polycrystalline superconducting wires that exhibit large critical current density Jc, which is limited by poor grain coupling and weak-link behavior at grain boundaries. Here, we report our recent achievement in the developing Sr0.6K0.4Fe2As2 tapes with transport Jc up to 0.1 MA/cm² at 10 T and 4.2K. This value is by far the highest ever recorded for iron based superconducting wires and has surpassed the threshold for practical application. The synergy effects of enhanced grain connectivity, alleviation of the weak-link behavior at grain boundaries, and the strong intrinsic pinning characteristics led to the superior Jc performance exhibited in our samples. This advanced Jc result opens up the possibility for iron-pnictide superconducting wires to win the race in high-field magnet applications. [ABSTRACT FROM AUTHOR]

The evolution of strontium (Sr) containing intermetallic phase in the eutectic reaction of Srmodified Al-Si hypoeutectic alloy was studied with high energy synchrotron beam source for nanodiffraction experiments and x-ray fluorescence elemental mapping. Contrary to popular belief, Sr does not seem to interfere with the Twin Plane Re-entrant Edge (TPRE) growth mechanism of eutectic Si, but evolves as the Al2Si2Sr phase during the eutectic reaction at the boundary between the eutectic Si and Al grains. [ABSTRACT FROM AUTHOR]

Conversion of fs supercontinuum to the ultraviolet (UV) range from 260 to 305 nm in nonlinear photonic crystal of strontium tetraborate is obtained. Spectral shape of generated UV radiation is governed by the shape of supercontinuum spectrum, focusing conditions and phase mismatch in the material of nonlinear photonic crystal. Maximum integral UV power of 2.6 μW was obtained in the case of weaker focusing, and peaks with the spectral width 1-3 nm dominate in the spectrum. Using tight focusing, broadband radiation in the range 265-300 nm was obtained. [ABSTRACT FROM AUTHOR]

The effect of d1 impurity doping in Sr-hexaferrite (SrM) on the magnetic anisotropy is investigated. First-principles calculations revealed that group-V elements (V, Nb) are stabilized with co-doping of alkali elements. Na1+/K1+ doping at Sr2+-site is found to be critical to form the d1 impurities at Fe-site. Experimentally, Na-V doped SrM shows the intrinsic coercivity of ∼5.4 kOe, which is ∼300% enhancement compared to undoped SrM and comparable value to La-Co co-doped SrM. Finally, the spin-orbit coupling from non-vanishing angular momentum of d1 impurity in SrM should be a main factor for such a substantial improvement of intrinsic coercivity. [ABSTRACT FROM AUTHOR]

We have used the ab initio random structure searching method together with density functional theory calculations to find stable structures of strontium under pressures up to 50 GPa. We predict a sequence of structural phase transitions and the stability of an orthorhombic structure of Cmcm symmetry above 25 GPa. Our energy, lattice dynamics, and molecular dynamics calculations confirm the stability of the Cmcm structure. The electron-phonon coupling calculations show that superconductivity arises in the bcc structure of compressed Sr and that it continues to exist in the Cmcm structure. The calculated superconducting transition temperatures are in good agreement with experiment. Our study gives an excellent account of the experimental observations. [ABSTRACT FROM AUTHOR]

The electrocaloric (EC) response of strontium titanate thin films is computed as a function of misfit strain, temperature, electric field strength, and electrode configuration using a nonlinear thermodynamic theory. For films in a capacitor configuration on compressive substrates, the transition between paraelectric and strain-induced ferroelectric tetragonal phases produces a large adiabatic temperature change, ΔT = 5 K, at room temperature for electric field changes ΔE = 1200 kV/cm. For films on tensile substrates, the transition between the paraelectric and strain-induced ferroelectric orthorhombic phases can also be accessed using inter-digitated electrodes (IDEs). The maximum EC response occurs for IDEs with a [110] orientation. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junctions based on manganites can exhibit a high tunneling magnetoresistance ratio due to the almost full spin polarization at the Fermi level. However, the performances of magnetic tunnel junction devices are also strongly linked to their noise characteristics. Here, we present a low frequency noise study on fully epitaxial La0.7Sr0.3MnO3/SrTiO3/La0.7Sr0.3MnO3/La0.66Sr0.33Mn0.995Ru0.005O3 tunnel spin valves with tunneling magnetoresistance ratios larger than 100%. We evidence non-conventional low frequency noise dependence on temperature related to the magnetic fluctuations and structural phase transitions in the structure. We present also a comparison with the low frequency noise exhibited in Fe/MgO/Fe magnetic tunnel junctions. [ABSTRACT FROM AUTHOR]

Theoretical analysis based on the Landau-Ginzburg-Devonshire theory is used to show that the joint action of flexoelectric effect and rotostriction leads to a large spontaneous in-plane polarization (∼1-5 μC/cm2) and pyroelectric coefficient (∼10-3 C/m2K) in the vicinity of surfaces of otherwise non-ferroelectric ferroelastics, such as SrTiO3, with static octahedral rotations. The origin of the improper polarization and pyroelectricity is an electric field we name flexo-roto field whose strength is proportional to the convolution of the flexoelectric and rotostriction tensors with octahedral tilts and their gradients. Flexo-roto field should exist at surfaces and interfaces in all structures with static octahedral rotations, and thus, it can induce surface polar states and pyroelectricity in a large class of otherwise nonpolar materials. [ABSTRACT FROM AUTHOR]

Erratum: "Surface anisotropy induced spin wave nonreciprocity in epitaxial La0.33Sr0.67MnO3 film on SrTiO3 substrate" [Appl. Phys. In the original published article,[1] the concentrations of La and Sr are reversed. This misprint does not change the identification or conclusion presented in the original published paper. [Extracted from the article]

We study the evolution of surface reconstructions on SrTiO3 (110) determined by cation concentration ratio and find it detectable by high energy electron diffraction (RHEED) even at high temperature up to 800 °C. The evaporation rate of Sr and Ti sources can be calibrated precisely by monitoring RHEED patterns in situ and in real time during the extended homogeneous oxide molecule beam epitaxy growth of SrTiO3 (110) film. High quality film is obtained with deviation of cation stoichiometry less than 0.5%. [ABSTRACT FROM AUTHOR]

We have studied the microstructure of LaNiO3-LaAlO3 superlattices using transmission electron microscopy in combination with electron energy loss spectroscopy. In superlattices grown on non-polar SrTiO3 substrates, nanometer-sized NiO precipitates form directly at the interface between the substrate and the initial LaNiO3 layer, while control measurements on polar substrates show no NiO. Because of the drastically different electronic properties of NiO and LaNiO3, such precipitates can strongly affect measurements on atomically thin LaNiO3-based films and multilayers on SrTiO3. In general, polarity-driven secondary phase formation should be carefully evaluated as a possible consequence of the polarity mismatch at metal-oxide interfaces. [ABSTRACT FROM AUTHOR]

Noncollinear random quasi-phase-matched frequency doubling in nonlinear photonic crystal (NPC) of strontium tetraborate (SBO) can be used for background-free autocorrelation measurements of ultrashort pulses in wide spectral range without any angular tuning of nonlinear photonic crystal. Nonuniformity of reciprocal superlattice vectors spectrum of random structure does not affect the accuracy of measurement. Nonlinear photonic crystals of strontium tetraborate are attractive medium for cross-correlation measurements in deep and vacuum ultraviolet. [ABSTRACT FROM AUTHOR]

We demonstrate a 60 nm channel length ferroelectric-gate field-effect transistor (FeFET) with thin-film transistor structure and good electrical properties. The FeFET contains three oxide thin-films: SrRuO3 (bottom gate electrode), Pb(Zr,Ti)O3 (ferroelectric), ZnO (semiconductor). The FeFET drain current-bottom gate voltage (IDS-VGS) characteristics show a high ON/OFF ratio of 105. The drain current ON/OFF ratio was about three orders of magnitude for write pulse widths as narrow as 10 ns. Although the channel length is set at 60 nm, the conductance can be changed continuously by varying the write pulse width. Good retention properties for three-level data were demonstrated. [ABSTRACT FROM AUTHOR]

Ruddlesden-Popper (R.P.) type faults have been investigated for Sr-excess SrTiO3 (STO) homoepitaxial thin films by pulsed laser deposition (PLD) and tuning of the laser fluence. The R.P. type fault structures were found to depend on the amount of excess Sr. The growth direction of the planer faults changed from normal to normal and parallel to the substrate surface with an increase in excess Sr. Due to the directional change of the planer faults, the out-of-plane lattice shows lattice expansion. The results suggest that we can control the planer fault structures in STO thin films simply by changing the laser fluence in the PLD method. [ABSTRACT FROM AUTHOR]

The defect structure of a homoepitaxial thin film of SrTiO3 containing excess Ti grown by pulsed laser deposition is investigated. The Sr/Ti ratio of the film is controlled to possess a slight excess of Ti by tuning the laser fluence. High-resolution transmission electron microscopy and electron energy loss spectroscopy studies reveal that the film contains Sr vacancies because of the presence of excess Ti. These vacancies tend to cluster as platelets several nanometers in diameter on (001) planes in the films. The SrO planes that contain the vacancy clusters exhibit lattice expansion due to Coulomb repulsion. [ABSTRACT FROM AUTHOR]

We have demonstrated that the resistance switching (RS) effect can be controlled by the modification of the electrode configurations and the carrier densities in the Ag/SrTiO3 and Ag/Nb-doped SrTiO3(Nb:STO) structures. The elimination of the Schottky junction in the metal/Nb:STO completely destroys the RS effect, which suggests that the RS effect originates from the modification of Schottky-like barrier formed at the interface of metal/Nb:STO. The rectifying I-V curves revealed that the change in resistance was attributed to the trapping or detrapping carriers at the interface. The carrier density plays an important role in the determination of RS effect. The presence of the RS in SrTiO3 requires an appropriate doping level to provide conditions for trapping carriers at the interface. [ABSTRACT FROM AUTHOR]

Density functional theory with local spin density approximation is applied to study the evolution of ferromagnetism in SrxPb1-xRuO3 (0≤x≤1). Besides the enhanced Pb-O covalence and Pb-Ru hybridization, the Jahn-Teller effect, which favors the low-spin state (S=0) of Ru4+ in a stretched oxygen octahedra, is found to be the origin of the observed paramagnetism in PbRuO3. With the introduction of Sr, the Pb-Ru hybridization is weakened and an intermediate-spin state (S=1) is preferred via the opposite Jahn-Teller effect in a compressed oxygen octahedra, leading to the appearance of ferromagnetism for x>0.5. Our calculations provide a good explanation of recent experimental findings. [ABSTRACT FROM AUTHOR]

Electronic transport properties of DyScO3/SrTiO3 polar heterointerface grown at different oxygen pressures are studied. This DyScO3/SrTiO3 polar heterointerface exhibits much higher charge mobility, up to 104 cm2 V-1 s-1, compared to the LaAlO3/SrTiO3 system due to relatively lower lattice mismatch between the film and substrate. More significantly, the DyScO3 film deposited under 10-4 mbar oxygen pressure presents an interfacial metal-to-semiconductor conducting mechanism transition at 90 K. Field effect transport measurement results reveal that this transition can be modulated by field effect through controlling the electron doping level of the interface originated from interfacial electronic reconstruction. [ABSTRACT FROM AUTHOR]

We have demonstrated that the resistance switching (RS) effect can be controlled by the modification of the electrode configurations and the carrier densities in the Ag/SrTiO3 and Ag/Nb-doped SrTiO3(Nb:STO) structures. The elimination of the Schottky junction in the metal/Nb:STO completely destroys the RS effect, which suggests that the RS effect originates from the modification of Schottky-like barrier formed at the interface of metal/Nb:STO. The rectifying I-V curves revealed that the change in resistance was attributed to the trapping or detrapping carriers at the interface. The carrier density plays an important role in the determination of RS effect. The presence of the RS in SrTiO3 requires an appropriate doping level to provide conditions for trapping carriers at the interface. [ABSTRACT FROM AUTHOR]

Ba0.75Sr0.25TiO3 film was epitaxially grown on a (001) LaAlO3 substrate using single-target pulsed laser deposition. The microstructure of the epitaxial film was investigated by conventional and high-resolution transmission electron microscopy. Apart from dislocations and stacking faults, two different kinds of antiphase boundaries, one being straight, and the other being zig-zagged, have been observed. The formation mechanism of these antiphase boundaries is discussed. [ABSTRACT FROM AUTHOR]

We have studied the surface termination of atomically flat SrTiO3 surfaces treated by chemical etching and subsequent thermal annealing, for all commercially available orientations (001), (110), and (111). Atomic force microscopy confirms that our treatment processes produce unit cell steps with flat terrace structures. We have also determined the topmost atomic layer of SrTiO3 surfaces through time-of-flight mass spectroscopy. We found that all three orientations exhibit a Ti-rich surface. Our observation opens doors for interface engineering along the [110] and [111] directions in addition to a well known [100] case, which widens the range of functional heterostructures and interfaces. [ABSTRACT FROM AUTHOR]

The effect of Sr vacancies on the behavior of strontium titanate with trivalent dopants (La3+, Gd3+, and Y3+) substituting Sr2+ ions is reported. A remarkable shift of the antiferrodistortive transition temperature Ta is revealed by Raman spectroscopy for just a small content of dopant. It is shown that a unique linear dependence of Ta versus tolerance factor is obtained when Sr-vacancies are taken into account. A vacancy size value of ∼1.54 Å is estimated, which is ∼7% larger than Sr2+ radius. This size difference enables explaining the unexpected increase of lattice parameter with increasing Bi3+ content in Sr1-1.5xBixTiO3. [ABSTRACT FROM AUTHOR]

We discuss the structural and electrical properties of scaled 2 nm HfO2/SrO gate stacks. Thin SrO layers are deposited by molecular beam epitaxy onto (001) p-Si substrates as alternative passivating interfacial layers (ILs) to SiO2. X-ray photoelectron spectroscopy and transmission electron microscopy show that, despite some HfO2-SrO intermixing, the SrO IL acts as a barrier against HfxSiy and SiO2 formation during high-κ deposition. Electrical measurements on metal-oxide-semiconductor capacitors with TiN metal gates integrated in a low-temperature process flow reveal an equivalent oxide thickness of 5 Å with competitive leakage current and hysteresis and a negative flat band voltage shift, suitable for n-channel transistors. [ABSTRACT FROM AUTHOR]

We have carried out magnetic Compton scattering measurements on polycrystalline samples of the perovskite manganites La1-xSrxMnO3 covering the hole-doping range from x=0.1 to x=0.5. Charge and magnetic Compton profiles were measured in order to obtain Compton profiles of spin-wise subbands. By considering the doping-dependency of the subband Compton profiles, we show how the electronic states evolve associated with hole doping. The results indicate that doped holes predominantly enter into the O 2p states in the lightly doped region and the charge transfer occurs from the up-spin Mn 3d to the down-spin Mn 3d states in the heavily doped region. [ABSTRACT FROM AUTHOR]