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Developing highly stable and efficient catalysts for oxygen evolution reaction (OER) is extremely important to sustainable energy conversion and storage, but improved efficiency is largely hindered by sluggish reaction kinetics. Dense and bimetal ruthenates have emerged as one of the promising substitutes to replace single-metal ruthenium or iridium oxides, but the fundamental understanding the role of A-site cations is still blurring. Herein, a family of lanthanides (Ln = all the lanthanides except Pm) are applied to synthesize pyrochlore lanthanide ruthenates (Ln2Ru2O7), and only Ln2Ru2O7 (Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu) with pure phase can be obtained by the ambient-pressure calcination. Compared with the perovskite ruthenates (SrRuO3) and rutile RuO2, the [RuO6] units in these Ln2Ru2O7 present the largely distorted configurations and different energy level splitting to prevent the excessive Ru oxidation and dissolution, which leads the primary improvement in the electrocatalytic OER performance. In the similar crystalline field split states, the charge transfer between [RuO6] units and Ln3+ cations also affect catalytic activities, even in the Ln2Ru2O7 surface reconstruction during the OER process. Consequently, Tb2Ru2O7 showed the highest OER performance among all the prepared Ln2Ru2O7 with similar morphologies and crystallization. This systematic work gives fundamental cognition to rational design of high-performance OER electrocatalysts in proper water electrolysis technologies.

Unexpected, yet useful functionalities emerge when two or more materials merge coherently. Artificial oxide superlattices realize atomic and crystal structures that are not available in nature, thus providing controllable correlated quantum phenomena. This review focuses on 4d and 5d perovskite oxide superlattices, in which the spin–orbit coupling plays a significant role compared with conventional 3d oxide superlattices. Modulations in crystal structures with octahedral distortion, phonon engineering, electronic structures, spin orderings, and dimensionality control are discussed for 4d oxide superlattices. Atomic and magnetic structures, Jeff = 1/2 pseudospin and charge fluctuations, and the integration of topology and correlation are discussed for 5d oxide superlattices. This review provides insights into how correlated quantum phenomena arise from the deliberate design of superlattice structures that give birth to novel functionalities. [ABSTRACT FROM AUTHOR]

This paper presents structural, detailed magnetic, and exchange bias studies in polycrystalline Ba 2 ScRuO 6 synthesized at ambient pressure. In contrast to its strontium analogue, this material crystallizes in a 6L hexagonal structure with space group P 3 ¯ m1. The Rietveld refinement using the room-temperature powder XRD pattern suggests a Ru-Sc disorder in the structure. The temperature variation of the DC electrical resistivity highlights a semiconducting behavior with the electron conduction corresponding to Mott's 3D variable range hopping (VRH) model. The detailed magnetization measurements show that Ba 2 ScRuO 6 develops antiferromagnetic ordering at T N ≈ 9 K. Interestingly, below 9 K (T N ), the field-cooled magnetic field variation (FC) of the magnetization curves highlights an exchange bias effect in the sample. The exchange bias field reaches a maximum value of 1.24 kOe at 2 K. The exchange bias effect below the magnetic ordering temperature can be attributed to the inhomogeneous magnetic correlations due to the disorder in the structure. Remarkably, the appearance of a large exchange bias field in Ba 2 ScRuO 6 indicates that inhomogeneous hexagonal double perovskites are a promising class to explore new materials having potential applications in spintronics. [ABSTRACT FROM AUTHOR]

Herein, a systematic mechanism behind long‐range ferromagnetic (FM) ground state is described based on 4d–4f interactions demonstrated in strongly correlated Ba2DyRuO6 and Ba2TmRuO6 double‐perovskite (DP) systems. Density functional theory (DFT) + U based possible half‐metallic FM nature of the considered DPs is realized along with integer values of spin magnetic moments (8.0 and 3.0 μB f.u.−1, respectively). This robust FM configuration is mainly dependent on Ru5+ and rare‐earth (RE3+) elements highlighting the importance of B‐site cationic ordering approach used in present study. The optical response of considered rare‐earth ruthenate DPs is also scrutinized, implying their potential usage in optical filter devices. The DFT + U based results are validated via comparing with existing experimental literature. This study suggests Ba2DyRuO6 and Ba2TmRuO6 as a novel addition to the family of half metals and will surely pave the way for materialists to experimentally explore their physical features for spintronic usage. [ABSTRACT FROM AUTHOR]

Double perovskites (DP's) are important for understanding the diverse physical properties arising from strongly correlated interactions. According to experimental observations, the DP's A 2 SmRuO 6 (A = Ba & Sr) are insulators; however, first-principles calculations using GGA approximations show that they are metallic. We observed a band gap (E g) opening of 1.3 eV for Ba 2 SmRuO 6 (BSRO) and 1.4 eV for Sr 2 SmRuO 6 (SSRO) upon the insertion of Hubbard parameter (U) in the theoretical computations for accounting the electron-electron interactions. Further investigations using core-level spectroscopy reveal E g of 1.05 eV for BSRO and 0.85 eV for SSRO. Furthermore, the calculations for Δ (charge transfer energy), U (coulomb repulsion energy), and W (bandwidth) from the combined spectra show U < Δ and U/W > 1.15, which confirms these compounds be classified as Mott-Hubbard insulators. These results expand our understanding of the strongly correlated compounds around the Fermi level, which might have applications in optoelectronics. [Display omitted] • The double perovskite compounds A 2 SmRuO 6 (A = Ba & Sr) show an insulating nature from the experimental results; however, these compounds are metallic (GGA-based first principles calculations). • To investigate this we incorporated different core level spectroscopic tools to investigate the electronic states, and introduced the Hubbard parameter in theoretical calculations. • From the core level spectra (UPS and XAS), the charge transfer energy (Δ), coulomb repulsion energy (Δ), and band-width (W) results into (i) U<Δ and (ii) U/W>1.15, which shows that these compounds are Mott-Hubbard insulator type. [ABSTRACT FROM AUTHOR]

This paper presents structural, detailed magnetic, and exchange bias studies in polycrystalline Ba2ScRuO6 synthesized at ambient pressure. In contrast to its strontium analogue, this material crystallizes in a 6L hexagonal structure with space group P3¯m1. The Rietveld refinement using the room-temperature powder XRD pattern suggests a Ru-Sc disorder in the structure. The temperature variation of the DC electrical resistivity highlights a semiconducting behavior with the electron conduction corresponding to Mott’s 3D variable range hopping (VRH) model. The detailed magnetization measurements show that Ba2ScRuO6 develops antiferromagnetic ordering at TN≈ 9 K. Interestingly, below 9 K (TN), the field-cooled magnetic field variation (FC) of the magnetization curves highlights an exchange bias effect in the sample. The exchange bias field reaches a maximum value of 1.24 kOe at 2 K. The exchange bias effect below the magnetic ordering temperature can be attributed to the inhomogeneous magnetic correlations due to the disorder in the structure. Remarkably, the appearance of a large exchange bias field in Ba2ScRuO6 indicates that inhomogeneous hexagonal double perovskites are a promising class to explore new materials having potential applications in spintronics.

Thin films of perovskite ruthenates of the general formula ARuO3 (A = Ca and Sr) are versatile electrical conductors for viable oxide electronics. They are also scientifically intriguing, as they exhibit nontrivial electromagnetic ground states depending on the A‐site element. Among them, realization of the cubic perovskite (3C) BaRuO3 in thin film form has been a challenge so far, because the 3C phase is metastable with the largest formation energy among the various polymorph phases of BaRuO3. In this study, 3C BaRuO3 thin films are successfully prepared employing epitaxial stabilization. The 3C BaRuO3 thin films show itinerant ferromagnetism with a transition temperature of ≈48 K and a non‐Fermi liquid phase. The epitaxial stabilization of the 3C BaRuO3 further enables to make a standard comparison of perovskite ruthenates, thereby establishing the importance of the RuO orbital hybridization in understanding the itinerant magnetic system. [ABSTRACT FROM AUTHOR]

Magnetism in double perovskite oxides of the formula A2BB'O6 has been a subject of great interest and intensive research in condensed matter physics. In this paper, Ln2CuRuO6 (A = La, Pr) samples were synthesized by solid-state reaction method, and we investigated their structural and magnetic properties. The new double perovskite compound Pr2CuRuO6 stabilizes in the monoclinic P21/n structure with an antisite defect fraction of ~ 3% between Cu and Ru sites. Our structural analysis indicates the severe deformation of Cu-O-Ru bond angle, as La3+ is replaced by the smaller rare earth ion Pr3+. For Pr2CuRuO6, the observed ferromagnetic transition temperature (Tc = 32 K) is higher than that of La2CuRuO6 (Tc = 15 K), which may be possibly associated with the enhanced magnetic interaction due to the distorted Cu-O-Ru bond angle. In addition, the anomalous phenomenon of ZFC susceptibility at low temperature suggests a degree of magnetic frustration and can be attributable to the intrinsic antisite defect in Pr2CuRuO6. The first principle calculations confirm a ferromagnetic Cu-Ru exchange interaction in Pr2CuRuO6, which is different from the antiferromagnetic case for La2CuRuO6. [ABSTRACT FROM AUTHOR]

Noncollinear spin textures such as skyrmions lead to a novel Hall effect contribution called the topological Hall effect. In recent years, research has focused on the Weyl metal SrRuO3 with topological signatures reported for SrRuO3 layers adjacent to layers with strong spin–orbit coupling. However, SrRuO3 films are known to be prone to structural modifications when interfaced with different materials. In this work the Hall effect of SrRuO3/La0.7Sr0.3MnO3 superlattices (SLs) is correlated with structural and magnetic information to study whether a topological Hall effect is induced by interfacing to ferromagnetic layers. High‐quality SLs with ultrathin layers are fabricated by pulsed laser deposition on SrTiO3 substrates. The symmetry of the SrRuO3 layers is studied by angular magnetoresistance measurements and the magnetocrystalline anisotropy by magnetization measurements. Two SLs are compared in detail, both with 8 unit cell thick SrRuO3 layers, but with La0.7Sr0.3MnO3 layers 2 and 4 unit cell thick. Only the sample with 2 unit cell thick manganite layers shows features resembling a topological Hall effect. Depending on the La0.7Sr0.3MnO3 layer thickness the SrRuO3 crystalline symmetry is orthorhombic or tetragonal. The results indicate that the topological Hall effect features arise from an intricate interplay between magnetocrystalline anisotropy and antiferromagnetic interlayer coupling. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The magneto-optical spectrum, with magnetic fields up to 42 T, of double layered ruthenates Ca 3 (Ru 0.91 Mn 0.09) 2 O 7 (CRMO) single crystal is studied. Both the temperature and magnetic field induced insulator-to-metal transitions (IMTs) are observed via magneto-optical properties of the crystal. The critical magnetic field (H // c) of IMT for CRMO is found to be as large as 35 T at 5 K. The fine structure of optical spectra identified the antiferromagnetic/ferro-orbital-ordering configurations of Ru 4 d orbitals at low temperatures. Meanwhile, the configuration of orbital polarization of such double-layer CRMO single crystal is discussed. These results suggest that the orbital degree of freedom plays an important role in the field induced IMT of multi-orbital system. [ABSTRACT FROM AUTHOR]

Single crystals of the quaternary R‐type ferrites BaLiRu5O11 [a = 11.628(6) Å, c = 13.7596(5) Å], and BaCu1+xRu5–xO11 [a = 11.6825(6) Å, c = 13.8051(7) Å], and their quinary solid solution BaLi1–xCux+δRu5–δO11 [a = 11.6453(2) Å, c = 13.7772(3) Å] were obtained by flux growth technique. X‐ray diffraction reveals the compounds to crystallize in space group P63/m with Z = 8. Measurements of the magnetic susceptibility of BaLiRu5O11 and BaCu1+xRu5–xO11, applying Curie–Weiss fits, confirm their paramagnetic behavior with temperature independent contributions of χ0,mol = 3.27 × 10–3 cm3·mol–1 and χ0,mol = 2.47 × 10–3 cm3·mol–1, respectively. Furthermore, the valence state of Ru in BaLiRu5O11 and BaCu1+xRu5–xO11 was determined to +3.8 by X‐ray absorption spectroscopy. Cu in BaCu1+xRu5–xO11 is dominating in a +2 state according to X‐ray photoelectron and X‐ray absorption spectroscopy, while a minor amount in +1 state may represent the excess copper substituting some Ru within a distorted Kagome net arrangement. [ABSTRACT FROM AUTHOR]

Abstract: In this ultrashort review we consider several ruthenates having layered structure with the Ru ions forming a honeycomb lattice (SrRu2O6, AgRuO3, Li2RuO3, Na2RuO3, and α-RuCl3). Depending on the number of d-electrons and Ru-Ru bond length these materials demonstrate very different physical properties. [ABSTRACT FROM AUTHOR]

Here, we report the study of structural and magnetic behavior of SrRuO 3 by Ga doping at Ru site. SrRuO 3 has an orthorhombic structure of Pbnm symmetry that has not changed by Ga doping, however, lattice parameters has decreased. The SrRuO 3 is the one and only example of 4 d based itinerant ferromagnet (FM) in oxides with transition temperature (T c) ∼ 160 K. Below T c , SrRuO 3 shows large bifurcation between Zero-field-cooled (ZFC) and field-cooled (FC) magnetization, which decreases by Ga doping. The inverse susceptibility (χ −1) in paramagnetic (PM) and high-temperature region shows that the Curie temperature (θ p) as well as effective moment decreases by Ga doping. The isothermal magnetization at 5 K shows hysteresis, which retain by Ga doping though the moment decreases. The Arrott plot confirms the FM nature and gives spontaneous magnetization (M S) that decreases by Ga doping. [ABSTRACT FROM AUTHOR]

Interfaces between dissimilar correlated oxides can offer devices with versatile functionalities, and great efforts have been made to manipulate interfacial electronic phases. However, realizing such phases is often hampered by the inability to directly access the electronic structure information; most correlated interfacial phenomena appear within a few atomic layers from the interface. Here, atomic-scale epitaxy and photoemission spectroscopy are utilized to realize the interface control of correlated electronic phases in atomic-scale ruthenate-titanate heterostructures. While bulk SrRuO 3 is a ferromagnetic metal, the heterointerfaces exclusively generate three distinct correlated phases in the single-atomic-layer limit. The theoretical analysis reveals that atomic-scale structural proximity effects yield Fermi liquid, Hund metal, and Mott insulator phases in the quantum-confined SrRuO 3 . These results highlight the extensive interfacial tunability of electronic phases, hitherto hidden in the atomically thin correlated heterostructure. Moreover, this experimental platform suggests a way to control interfacial electronic phases of various correlated materials., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

Magnetic properties of bulk polycrystalline Mn-doped SrRu 1− x Mn x O 3 perovskite, at doping range 0.2≤ x ≤0.3, were studied by both magnetization and ac-susceptibility measurements. It was found that the exchange bias (EB) effect emerges with increasing Mn doping in SrRu 1− x Mn x O 3 at x ≈0.25, following the ferromagnetic (FM) to antiferromagnetic (AFM) phase transition. This transition is accompanied with the change in structure symmetry and then the EB field, H EB , increases significantly in doping range 0.25< x ≤0.3. The EB effect was verified by both cooling magnetic field, H cool , dependence of the H EB and training effect. A markedly nonmonotonic H EB vs. H cool dependence with maximum at around 40 kOe was found, resembling the behavior of phase-separated EB systems. Moreover, a clear analogy with behavior of classic EB system of Pr 1/3 Ca 2/3 MnO 3 was noticed, strongly suggesting that the EB effect in SrRu 1− x Mn x O 3 originates from exchange interactions at the interface of nanoscale FM clusters (size of ~1.6 nm at x =0.3) coe x isting together with dominant AFM phase at the boundary of the first-order FM/AFM transition. The training effect observed is well understandable within the spin-configuration relaxation model and indicates important contribution to the EB behavior from the AFM domains rearrangement at the interface. [ABSTRACT FROM AUTHOR]

I review many-body effects on the resistivity of a multi-orbital system beyond Landau's Fermi-liquid (FL) theory. Landau's FL theory succeeds in describing electronic properties of some correlated electron systems at low temperatures. However, the behaviors deviating from the temperature dependence in the FL, non-FL-like behaviors, emerge near a magnetic quantum-critical point (QCP). These indicate the importance of many-body effects beyond Landau's FL theory. Those effects in multi-orbital systems have been little understood, although their understanding is important to deduce ubiquitous properties of correlated electron systems and characteristic properties of multi-orbital systems. To improve this situation, I formulate the resistivity of a multi-orbital Hubbard model using the extended Éliashberg theory and adopt this method to the inplane resistivity of quasi-two-dimensional paramagnetic ruthenates in combination with the fluctuation-exchange approximation including the current vertex corrections arising from the self-energy and Maki-Thompson term. The results away from and near the antiferromagnetic QCP reproduce the temperature dependence observed in Sr2RuO4 and Sr2Ru0.075Ti0.025O4, respectively. I highlight the importance of not only the momentum and the temperature dependence of the damping of a quasiparticle but also its orbital dependence in discussing the resistivity of correlated electron systems. [ABSTRACT FROM AUTHOR]

RuSrGdCuO and SrYbRuCuO were synthesized using a solid-state reaction. X-ray diffraction showed that RuSrGdCuO crystallized into the tetragonal Ru-1212 structure (space group P4/mmm), whereas the SrYbRuCuO had a monoclynic structure (space group P2/n). SrYbRuCuO showed a possible magnetic transition ( T) at 44 K with a superconducting transition temperature T at 30 K. In contrast, RuSrGdCuO showed a magnetic transition at 140 K with a T at 25 K. The magnetization data for SrYbRuCuO suggests that this sample exhibits antiferromagnetic ordering in zero-field-cooled (ZFC) magnetization, whereas it reveals a weak ferromagnetic component during field-cooled (FC) cycles. In addition, larger diamagnetic signals were observed during FC cycle compared to the ZFC. These results suggest that the valence state of the Yb ion have a significant effect on the magnetic state of the SrYbRuCuO superconductor. [ABSTRACT FROM AUTHOR]

Abstract: We report structural, detailed DC and linear/non-linear AC, isothermal and thermoremanent magnetization study of the rutheno-cuprate superconducting ferromagnet RuSr2Gd1.4Ce0.6Cu2O10−δ (GdRu-1222). Structural analysis, by employing Rietveld refinement of X-ray diffraction pattern, reveals that GdRu-1222 crystallizes in tetragonal phase with I4/mmm space group. GdRu-1222 is a reported superconducting ferromagnet with Ru spins magnetic ordering at around 110K and superconductivity below 40K in Cu–O2 planes. Detailed linear/non-linear first and higher order harmonic of AC susceptibility studies unveiled the complex magnetism of GdRu-1222. A frequency dependent cusp is observed in AC susceptibility (χ ac ) vs. T measurements. The change in cusp position with applied frequency followed the well known Vogel–Fulcher law, which is a feature to describe a spin-glass (SG) system with possibility of embedded homogeneous/non-homogeneous magnetically interacting/non-interacting ferromagnetic clusters. Such an interpretation is also supported by thermoremanent magnetization (TRM) study at T=60K. Detailed interpretation of AC magnetization results revealed the formation of magnetic (ferromagnetic) homogenous/non-homogenous clusters of different sizes embedded in spin-glass (SG) matrix. The magnetization vs. applied field loops do not saturate, even at high applied fields (50kOe), resulting in the short-range magnetic ordering in the system, which causes the formation of clusters that freeze at low temperatures. Temperature variation of first- and third-order susceptibility harmonics show good agreement with the Wohlfarth's model (WM), leading to the superparamagnetism (SPM) state. Detailed magnetization (DC and AC both) results and their analysis helped in explaining the temperature dependent magnetism of the GdRu-1222 system. [Copyright &y& Elsevier]

We have investigated the specific heat, thermal expansion and thermodynamic properties of BaRuO3in rhombohedral, hexagonal and cubic phase using the modified rigid ion model (MRIM) by incorporating the effect of lattice distortions. The calculated Debye temperature, specific heat and other thermal properties reproduce well with the available experimental data, implying that MRIM represents properly the nature of the perovskite-type BaRuO3. Besides, we have reported the thermal expansion (α), bulk modulus (B), cohesive energy (ϕ), molecular force constant (f), Reststrahlen frequency (υ), Debye temperature (θD), and Gruneisen parameter (γ). [ABSTRACT FROM PUBLISHER]

Abstract: The oxygen stoichiometries of pure and rare-earth substituted La2RuO5 have been investigated by thermogravimetry (TG) in reducing atmosphere. Assuming that the observed total weight loss is caused by the reduction of Ru4+ to Ru-metal, remarkable oxygen deficiencies were calculated. These would correspond to ruthenium oxidation states significantly lower than the ones experimentally observed by XANES. To explain this discrepancy we investigated the reduction products by X-ray absorption spectroscopy (XAS). EXAFS measurements at the Ru–K edge revealed the presence of an X-ray amorphous ruthenium oxide, indicating an incomplete reduction. The apparent oxygen deficiencies obtained for pure and rare-earth substituted samples correlate with the amount of remaining ruthenium oxide. The presence of a ruthenium oxide species was furthermore verified by Ru–LIII XANES investigations. Our results show that the determination of oxygen contents by thermogravimetry might fail even for the easily reducable nobel metal oxides and therefore has to be applied with caution if the reaction products cannot be identified unambiguously. [Copyright &y& Elsevier]

Abstract: The changes in magnetic stabilization energy with volume for SrRuO3 are examined by means of the density functional theory calculations with on-site Coulomb interaction corrections to Ru 4d electrons. A robust magnetic ground state for SrRuO3 is found even when its volume is compressed to a value close to the experimental volume of the nonmagnetic (NM) CaRuO3. Nevertheless, the important ferromagnetic (FM) and half-metallic (HM) characters of SrRuO3 are found to destabilize during the process of volume compression. Corresponding to the change from FM to antiferromagnetic (AFM) character, the electrical property of the compound changes from conducting into insulating. The electronic structure calculations for SrRuO3 under various volume-compression cases show that the loss of HM is due to Ru 4d states in minority band of SrRuO3 being pushed away from Fermi level. Further examination to the atomic positions before and after volume compression suggests the dramatic change of density of states at Fermi level may be due to the giant internal atomic displacements of Sr/O in SrRuO3. [Copyright &y& Elsevier]

The properties of manganite/ruthenate superlattices are reviewed with a specific focus on the manganite/ruthenate interface. La0.7Sr0.3MnO3/SrRuO3 and Pr0.7Ca0.3MnO3/SrRuO3 superlattices grow with a high crystalline perfection as illustrated in the figure to the right: at the interface the individual cation species can be clearly identified, interdiffusion is marginal. The superlattices show magnetization processes with an intricate interplay between magnetocrystalline anisotropy, size of the layer magnetization, spin confinement and interfacial antiferromagnetic interlayer coupling. There is further an unprecedented Curie temperature stabilization at room temperature values of the La0.7Sr0.3MnO3 layers in the superlattices down to layer thicknesses of one unit cell. The magnetotransport properties, especially the Hall effect, indicate the existence of a quasi-two-dimensional hole gas at the La0.7Sr0.3MnO3/SrRuO3 interface; this is further supported by an analysis of cation displacements as determined from scanning transmission electron microscopy. The manganite/ruthenate interface might be considered as a model system for the study of interfacial reconstruction and charge transfer in a highly correlated ferromagnetic system. [ABSTRACT FROM AUTHOR]

Abstract: We present a brief review of the physical properties of Sr3Ru2O7, in which the approach to a magnetic-field-tuned quantum critical point is cut off by the formation of a novel phase with transport characteristics consistent with those of a nematic electronic liquid crystal. Our goal is to summarise the physics that led to that conclusion being drawn, describing the key experiments and discussing the theoretical approaches that have been adopted. Throughout the review we also attempt to highlight observations that are not yet understood, and to discuss the future challenges that will need to be addressed by both experiment and theory. [Copyright &y& Elsevier]

Thermodynamic and transport properties of the CaRu1- xTi xO3 system with x = 0, 0.03, 0.07, 0.10, and 0.15 in magnetic field up to 9 T have been studied. The unconventional temperature dependences of magnetic susceptibility, specific heat, and electrical resistivity observed for CaRuO3 are typical for non-Fermi liquids and they support the assumption about the proximity of the system to the quantum critical point. The analysis of the experimental results suggests the electronic phase separation in CaRuO3 into ferromagnetic itinerant regions coexisting with strongly correlated ones. Substitution by titanium seems to push the system towards ferromagnetism, and drives it away from the quantum criticality. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, structural and electrical transport properties of hexagonal, 4H-type, BaRu1−x Mn x O3 , synthesized by the solid-state reaction method at ambient pressure, have been presented. Electrical transport properties are measured over a temperature range of 10–300K in the magnetic field up to 15kOe. The low temperature resistivity shows a quadratic temperature dependence for the x=0 sample and a crossover from a T 2 to a temperature dependence, corresponding to the Fermi-liquid phase to a non-Fermi-liquid phase crossover, in the x=0.03 sample. Furthermore, Mn doping drives the system from the metallic state at x=0 to the insulating state , in which the x=0.3 sample shows a variable range hopping behavior below 100K. At low temperature region, large magnetoresistance was observed for the samples with x=0.2 and 0.3. [Copyright &y& Elsevier]

Abstract: We have calculated the electronic structure of SrRu1−x Mn x O3 using the full potential linearized augmented plane wave method by LSDA and LSDA+U. The antiparallel alignment between the Mn and Ru ions are consistent with the competition between ferromagnetism and antiferromagnetism in the low Mn-doped polycrystalline samples. This is in contrast to the appearance of quantum critical point and FM and AFM transitions in the single crystal measurement. Our results show that the discrepancy between different experimental phase diagrams is related to the conditions of sample preparation and also the difference between the degree of magnetic interactions between the Mn and Ru moments. The DOS and the calculated Mn magnetic moment is similar to the magnetic moment of a purely ionic compound with d 3 configuration. The AFM state has band gap of 1.2eV at the Fermi energy predicting an insulating behavior. [Copyright &y& Elsevier]

Abstract: We have prepared polycrystalline single-phase ACo2+x Ru4−x O11 (A=Sr, Ba; 0≤ x ≤0.5) using the ceramic method and we have studied their structure, electrical resistivity and Seebeck coefficient, in order to estimate their power factor (P.F.). These layered compounds show values of electrical resistivity of the order of 10−5 Ωm and their Seebeck coefficients are positive and range from 1μVK−1 (T =100K) to 20μVK−1 (T =450K). The maximum power factor at room temperature is displayed by BaCo2Ru4O11 (P.F.: 0.20μWK−2 cm−1), value that is comparable to that shown by compounds such as SrRuO3 and Sr6Co5O15. [ABSTRACT FROM AUTHOR]

Abstract: Na27Ru14O48 has been synthesized in air at 700°C. The composition and crystal structure of the phase were determined by single crystal X-ray diffraction. The triclinic crystal structure contains isolated planar Ru7O24 plaquettes made from seven edge-sharing RuO6 octahedra. The complex Na:Ru ratio is a result of tilting of the plaquettes to disrupt the packing of nominally hexagonal close packed planes made of Na ions and RuO6 octrahedra. Resistivity measurements show that the material is semiconducting with an activation energy of 0.53eV. The observed magnetic moment of 3.11 μ B per Ru is lower than the expected spin only value, but is within the range seen in other compounds and is too large to indicate that the fundamental magnetic entities are the isolated Ru7O24 plaquettes. Small, reproducible deviations in the Curie–Weiss behavior occur below 200K and the onset of a broad magnetic transition is seen between 40 and 32K. [ABSTRACT FROM AUTHOR]

We report on experiments of the bulk susceptibility χ( T), heat capacity C( T)/ T, resistivity ρ( T) and nuclear resonances (NMR and NQR) in order to review evidence of quantum critical behaviour in some metallic transition-metal oxides. In analogy to the conventional 4 f- and 5 f-electron based heavy-fermion compounds, the prerequisites of quantum criticality, i.e. a magnetic phase transition at T=0 accompanied by non-Fermi liquid behaviour, are observed in LiVO which was the first transition-metal oxide showing heavy-fermion properties. Furthermore, we investigate the large group of copper-ruthenates of the composition ACuRuTiO which also demonstrate heavy-fermion and non-Fermi liquid properties. For LaCuRuTiO we establish a magnetic phase diagram where the substitution of titanium by ruthenium cations suppresses long-range magnetic order in favour of a magnetic quantum critical point, which comes along with a metal-to-insulator transition. Our experiments elucidate open questions concerning the nature of the heavy-fermion properties, intermediate valence, and the origin of the metal-to-insulator transition. Specifically, the role of the ruthenium and copper d-electrons is addressed: the metal-to-insulator transition turns out to correlate with the increasing itinerancy of local moments at the Cu site in our doping experiments. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated the electronic structure of Sr(Ca)Ru1−x Cr x O3 using the full potential linearized augmented plane wave method by different approximation such as LSDA and LSDA+U. The LSDA calculation suggest that Cr4+–Ru4+ hybridization is responsible for the high Curie temperature T C in SrRu1−x Cr x O3, but it cannot completely describe its physical behavior. Our LSDA+U DOS results for SrRu1−x Cr x O3 clearly establishes renormalization of the intra-atomic exchange strength at the Ru sites, arising from the Cr–Ru hybridization. The antiferromagnetic coupling of Cr3+ with Ru4+,5+ lattice increases the screening, which is consistent with the low magnetic moment of the Ru ions. The more distorted Ca-based compounds as compared to the Sr-based systems shows that the hybridization mechanism is not relevant for these compounds. The bigger exchange splitting of Ru 4d and Cr 3d at the Fermi level with Ru4+,5+ and Cr3+,4+ orbital occupancies of CaRu0.75Cr0.25O3 in the LSDA+U calculation, compared with that of the LSDA calculation, shows that repulsion between electrons tend to keep the localized spins from overlapping. The low screening of the Ru t 2g electrons increases T C in the Ca-based systems, which is consistent with the both high Ru exchange splitting and magnetic moment. The insulating behavior of the high Cr-doped systems can be explained by considering the charge transfer. [Copyright &y& Elsevier]

Abstract: We have investigated the transports of micro-fabricated sample of 3-K phase superconductivity (T c ∼3K) in Sr2RuO4–Ru eutectic system in order to clarify the pairing symmetry. Up to now, pure Sr2RuO4 (T c =1.5K: 1.5-K phase) is widely recognized to be a spin-triplet odd-parity superconductor. However, the enhancement mechanism of T c up to 3K and the pairing symmetry of the 3-K phase have not been cleared yet. By using micro fabrication technique with focused ion beam, we have succeeded to extract individual superconducting channels for the 3-K phase in which only a few pieces of Ru inclusions are contained. Multiple kink structures observed in differential resistance–current (dV/dI − I) characteristics indicate serially connected superconducting filaments in the 3-K phase. We confirm that the 3-K phase is an odd-parity superconductor similar to pure Sr2RuO4 from the monotonous temperature dependence of the critical currents. In addition, we observed a quite unusual hysteresis in dV/dI − I below 2K, which suggests the internal degrees of freedom in the superconducting state: the most probably the chiral p-wave state. [Copyright &y& Elsevier]

Abstract: It is widely believed that cuprate (CuO2) planes are the essential structural component of all high temperature superconductors. In contrast, Wu et al. and Chen et al. have published evidence for superconductivity in Cu-doped double pervoskites which consist of alternating layers of either SrO or BaO with YRu1− u Cu u O4. These structures have no cuprate planes, yet exhibit diamagnetism to temperatures as high as 84K. Since the chemical components of these materials are common to the rutheno-cuprates, it is widely believed that impurity phases are responsible for the observed superconductivity. Impurity phase formation and decomposition in a homolog, Ba2GdRu1− u Cu u O6, is investigated. It is found that this phase is stable against separation into GdBa2Cu3O7 and Ba2GdRuO6. GdBa2Cu3O7 does not survive high temperature processing with Ba2GdRuO6. [Copyright &y& Elsevier]

Abstract: We have developed a novel way to perform de Haas–van Alphen (dHvA) measurements under high pressure using a microcoil system in an anvil cell, allowing us to track the electronic structure of strongly correlated electronic systems as a function of pressure. The unconventional superconductor Sr2RuO4 is chosen to illustrate the feasibility of this technique. The dHvA frequencies are obtained from the oscillatory data and they are compared with the values reported earlier in the literature. The quasiparticle effective masses are extracted from our high resolution dHvA data. [Copyright &y& Elsevier]

Muon spin rotation (μ+SR) measurements conducted on crystalline YBa2Cu3O7 are consistent with s-wave pairing, not d-wave, suggesting that the superconducting hole condensate resides in the BaO layers, not in the cuprate-planes. The specific heat and thermal conductivity data are explained by the superconducting BaO layers alone, unlike the failed interpretation based on CuO2-plane superconductivity. The layer charges of the CuO2 planes are almost -2 |e|, indicating that those planes are primarily carriers of electrons, not holes. The cuprate-planes are not the dominant hole-carriers of high-TC superconductivity, as demonstrated by doped YBa2RuO6, which has no such CuO2 lanes, yet superconducts at ~ 93 K. Moreover the trio of related compounds, YSr2RuO6 (doped with Cu on Ru sites), undoped GdSr2Cu2RuO8, and undoped Gd2-zCezSr2Cu2RuO10 all start superconducting near 49 K in their SrO layers, not in the cuprate planes of the two compounds that have such planes, because those planes are either antiferromagnetic or weakly ferromagnetic and so do not superconduct. In PrBa2Cu3O7, a Pr-on-Ba-site (PrBa) defect kills the superconductivity, but Pr-on-Pr-site (PrPr) does not. Both defects are approximately equidistant from the intervening cuprate plane, suggesting that the cuprate plane does not carry significant superconductivity. In GdBa2Cu3O7, Gd-on-a-Gd-site (GdGd) does not break Cooper pairs, but Gd-on-a-Ba-site (GdBa) does, indicating that the superconductivity is in the BaO layers, and not in the cuprate-planes. In HgBa2Can-1CunO2n+2, the BaO layers, not the cuprate-planes, gain positive charge as TC, pressure, and the number of layers n increase. The reason that theories based on holes in the cuprate-planes have done so poorly is that those planes were incorrectly identified as the source of high-temperature superconductivity on the basis of a single datum by Cava et al., that was first contradicted by Jorgensen et al., and then endorsed by Jorgensen alone on the basis of the Cava datum, not his own. This error is the main reason why cuprate-plane superconductivity, which probably does not exist, has been so widely accepted. [ABSTRACT FROM AUTHOR]

Abstract: We report the synthesis and magnetization of Sr2RuREO6 (RE/Ru-211O6) with RE=Gd and Eu. Both Gd and Eu/Ru-211O6 are formed in distorted perovskite-type single phase with monoclinic P21/n space group. Magnetization (M/T) measurements exhibited antiferromagnetic ordering of Ru moments for both Gd and Eu compounds at a T N of around 30K due to super-exchange Ru–O–O–Ru interaction. Interestingly enough, detailed M/H plots of Gd/Ru-211O6 exhibited the development of a ferromagnetic (FM) component at 20K. Furthermore, below 10K, the FM component disappears, and rather spin freezing field (H SF) of around 1000Oe is seen at 5K. In case of Eu/Ru-211O6, the basic antiferromagnetic ordering of Ru moments remains invariantly down to 5K, and the appearance of the FM component is not seen. It seems that the high magnetic moment of 8μ B for Gd3+ influences the anti ferromagnetic (AFM) ordering of Ru in case of Gd/Ru-211O6. [Copyright &y& Elsevier]

Abstract: The discovery of an orbital ordering transition in provided an exciting link between ruthenate physics and that of the 3d transition metals. Despite clear evidence for the orbital ordering at (phase transition from a high temperature monoclinic structure to a low temperature triclinic structure accompanied by the opening of a spin gap), the atomic mechanism for this orbital ordering transition remains unresolved. We studied the local environment via Mössbauer effect (ME) measurements of 99Ru (97%) enriched samples over a temperature range of 4.2–196K. Fits to the spectra show that they arise solely from electric field gradients at the Ru sites without any hyperfine magnetic fields, ruling out the possibility of long range order. While the high temperature structure is accurately described by a single-site ME spectrum, the low temperature measurements can only be explained by a two-site model with significantly different symmetry at the two sites. At all temperatures the isomer shift is consistent with a oxidation state. [Copyright &y& Elsevier]

Abstract: Ferromagnetism can be studied in Compton scattering experiments, which use high-energy, elliptically polarised synchrotron radiation. The basis of the method and its interpretation in terms of site-specific moments will be explained and illustrated by a series of examples of archetypal compounds. For example, the hexaborides exhibit a wide range of electronic properties. Data will be presented for the heavy Fermion system CeB6 and the controversial ferromagnet Ca1− x La x B6. Undoped CeB6 exhibits a delocalised spin moment, more characteristic of the 5d than the 4f orbital. Whereas the magnetism in the Ca1− x La x B6 system has been suggested to be an extrinsic effect arising from iron contamination, our data indicate that the magnetism is intrinsic and inconsistent with what would be expected for an iron 3d moment. This supports the proposal that this system is, indeed, a weak itinerant ferromagnet. In Ru2SrGdCu208, we observe a combination of Gd 4f, Gd 5d and Ru 4d moments and the 5d moment appears to flip orientation below the Néel temperature. [Copyright &y& Elsevier]

Abstract: We have used the partial substitution of Cu by Zn and Ru by Sn to probe the normal, superconducting, and magnetic states in the superconducting and magnetically ordered ruthenocuprate RuSr2R2−y Ce y Cu2O10+δ (R=Eu, Gd). The effect of Zn substitution for Cu in the CuO2 planes is to suppress the superconducting transition temperature at a rate similar to that observed in other high temperature superconducting cuprates. Sn substitution for Ru rapidly suppresses the temperature where the ferromagnetic component is observed. This suppression rate depends on the Ce content. We observe that the temperature where the bulk Meissner phase commences is closer to the superconducting transition temperature when the ferromagnetic component is completely suppressed. This provides direct support for the spontaneous vortex phase model that has been applied to RuSr2Gd1.4Ce0.6Cu2O10+δ to account for coexisting magnetic and superconducting orders. [Copyright &y& Elsevier]

Abstract: The crystal structures, synthesis and physical properties of ruthenium hollandites ALi2Ru6O12 (A=Na, K) with a new pseudo-hexagonal structure type are described. Analogous to tetragonal hollandites, the framework is made of MO6 octahedra in double chains that share corner oxygens with each other to create interstitial tunnels. The tunnels are either hexagonal or triangular in cross-section. Magnetic susceptibilities, low temperature specific heat, and electrical resistivities are reported. The data indicate that these materials are normal, low density of states metals. This new structure type can be extended from A=Group I to A=Group II ions with the synthesis of CaLi2Ru6O12 and SrLi2Ru6O12. [Copyright &y& Elsevier]

A thermal study was performed on the RuSr2GdCu2O8 (Ru-1212) magnetic superconductor phase to investigate the effect of the annealing treatments in flowing O2 on the stability limit of the phase and on its structural, magnetic and transport properties. DTA-TG measurements were utilized to determine the decomposition process and the dependence of the decomposition temperature on the annealing atmosphere. The decomposition of the Ru-1212 phase was found sensitive to the oxygen partial pressure and increases with PO2 and the annealing time. The annealing treatments exert a depressing effect on the strength of the magnetic interaction, an enhancement on the superconductive properties and the vanishing of the magnetostriction. A decomposition reaction of Ru-1212 phase was proposed and discussed. [ABSTRACT FROM AUTHOR]