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The d5 electron configurations under the crystal field, spin–orbit coupling, and Coulomb interaction give rise to a plethora of profound ground states. Ruthenium perovskite oxides exhibit a number of unconventional properties yet the Ru4+ state (4 d 4 ) is usually stable in these materials. In this regard, Ru3+ ions in perovskite materials are expected to be a mesmerizing playground of 4 d 5 electron configurations. Here, we report measurements of x-ray photoemission spectroscopy on recently synthesized perovskite ruthenium oxide thin films, LaRuO3 and NdRuO3, whose valence state of the ruthenium ions is trivalent. We discuss correlation and spin–orbit effects from the valence band spectra, in particular an additional peak structure around 3–5 eV, reminiscent of the so-called 3 eV peak observed in Sr2RuO4. Moreover, we find that the core-level spectra of these materials are quantitatively different from those in other ruthenates, which possess Ru4+ ions, e.g., SrRuO3. We therefore argue that the core level spectra of LaRuO3 and NdRuO3 are peculiar to the Ru3+ states. [ABSTRACT FROM AUTHOR]

We studied the relationship between the lattice constant and magnetism of L 1 0 -ordered FePt under high pressure by means of first-principles calculations and synchrotron x-ray measurements. Based on our calculations, we found that the c/a ratio shows a local maximum at ∼20 GPa and that the Pt magnetic moment first remains almost unchanged and is sharply suppressed at ∼60 GPa. As for the c/a, we experimentally verified the local maximum at ∼20 GPa by powder x-ray diffraction. We also measured the x-ray magnetic circular dichroism at the Pt L edge up to ∼20 GPa. Any significant change in the Pt magnetic moment was not observed in agreement with the calculations. These results, thus, indicate that magnetic states, where the magnetization of Fe decreased and that of Pt did not change, can be created in L 1 0 -ordered FePt by lattice deformation under high pressure. [ABSTRACT FROM AUTHOR]

The strain effect from a substrate is an important experimental route to control electronic and magnetic properties in transition-metal oxide (TMO) thin films. Using hard x-ray photoemission spectroscopy, we investigate the strain dependence of the valence states in LaNiO3 thin films, strongly correlated perovskite TMO, grown on four substrates: LaAlO3, (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7, SrTiO3, and DyScO3. A Madelung potential analysis of core-level spectra suggests that the point-charge description is valid for the La ions, while it breaks down for Ni and O ions due to a strong covalent bonding between the two. A clear x-ray photon-energy dependence of the valence spectra is analyzed by the density functional theory, which points to the presence of the La 5p state near the Fermi level. [ABSTRACT FROM AUTHOR]

We present resonant soft x-ray scattering studies of Ti 3d and O 2p states at the interfaces of SrTiO3/LaAlO3 superlattices. From reflectivity analyses, focusing on the (003) peak which is forbidden for our “ideal” superlattice structure, we concluded that the LaO|TiO2/SrO and the SrO|AlO2/LaO interfaces have distinct reconstructions, breaking the heterostructure symmetry. [ABSTRACT FROM AUTHOR]

Control of the polarization of an X‐ray free‐electron laser (XFEL) has been performed using an X‐ray phase retarder (XPR) in combination with an arrival timing diagnostic on BL3 of the SPring‐8 Angstrom Compact free‐electron LAser (SACLA). To combine with the timing diagnostic, a pink beam was incident on the XPR crystal and then monochromated in the vicinity of samples. A high degree of circular polarization of ∼97% was obtained experimentally at 11.567 keV, which agreed with calculations based on the dynamical theory of X‐ray diffraction. This system enables pump–probe experiments to be operated using circular polarization with a time resolution of 40 fs to investigate ultrafast magnetic phenomena. [ABSTRACT FROM AUTHOR]

We characterized the electronic structure of LaVOx thin films by x-ray photoemission spectroscopy. We could distinguish the photoemission spectra among the x=3 phase (LaV3+O3), the x=4 phase (LaV5+O4), and the mixed phase regime. In the mixed phase, the surface was found to be mostly LaVO4. We could observe the evolution of the electronic structure in the growth phase diagram by systematically measuring core-level photoemission spectra. The V4+ component present in the x=3 phase may be due to charge transfer to avoid the polar catastrophe of the polar LaVO3 thin-film surface and/or to the oxidation of the surface. [ABSTRACT FROM AUTHOR]

We have investigated the Mn 3d partial density of states in SrTiO3(STO)/La0.6Sr0.4MnO3(LSMO) heterointerfaces as well as of LSMO films using Mn 2p-3d resonant photoemission spectroscopy. The strong enhancement of the Mn 3d spectra at the Mn 2p-3d threshold enables us to extract the Mn 3d spectra of LSMO layers in the vicinity of the interface with the STO overlayers. We have found that the spectral intensity of eg↑ states near the Fermi level is drastically reduced when the LSMO film is capped with STO overlayers. The close similarity in reduction of the intensity of the eg↑ states between the STO/LSMO interface and hole-doped LSMO films suggests that the hole doping into the LSMO layer close to the STO layer originates from the chemical carrier-concentration modulation at the valence-mismatched interface composed of the stacking sequence -TiO2-SrO-MnO2-La0.6Sr0.4O-, which is inevitable for multilayers based on perovskite oxides. [ABSTRACT FROM AUTHOR]

Ultrafast magnetization reversal of a ferrimagnetic metallic alloy GdFeCo was investigated by time-resolved resonant magneto-optical Kerr effect measurements using a seeded free electron laser. The GdFeCo alloy was pumped by a linearly polarized optical laser pulse, and the following temporal evolution of the magnetization of Fe in GdFeCo was element-selectively traced by a probe free electron laser pulse with a photon energy tuned to the Fe M-edge. The results have been measured using rotating analyzer ellipsometry method and confirmed magnetization switching caused by ultrafast heating. [ABSTRACT FROM AUTHOR]

We have studied the electronic structure of Li1+x[Mn0.5Ni0.5]1-xO2(x=0.00 and 0.05), one of the promising cathode materials for Li ion battery, by means of x-ray photoemission and absorption spectroscopy. The results show that the valences of Mn and Ni are basically 4+ and 2+, respectively. However, the Mn3+ component in the x=0.00 sample gradually increases with the bulk sensitivity of the experiment, indicating that the Jahn-Teller active Mn3+ ions are introduced in the bulk due to the site exchange between Li and Ni. The Mn3+ component gets negligibly small in the x=0.05 sample, which indicates that the excess Li suppresses the site exchange and removes the Jahn-Teller active Mn3+. [ABSTRACT FROM AUTHOR]

We have studied the electronic structure of Li1+x[Mn0.5Ni0.5]1-xO2 (x=0.00 and 0.05), one of the promising cathode materials for Li ion battery, by means of x-ray photoemission and absorption spectroscopy. The results show that the valences of Mn and Ni are basically 4+ and 2+, respectively. However, the Mn3+ component in the x=0.00 sample gradually increases with the bulk sensitivity of the experiment, indicating that the Jahn-Teller active Mn3+ ions are introduced in the bulk due to the site exchange between Li and Ni. The Mn3+ component gets negligibly small in the x=0.05 sample, which indicates that the excess Li suppresses the site exchange and removes the Jahn-Teller active Mn3+. [ABSTRACT FROM AUTHOR]

Strongly correlated electron systems often exhibit very strong interactions between structural and electronic degrees of freedom that lead to complex and interesting phase diagrams. For technological applications of these materials it is important to learn how to drive transitions from one phase to another. A key question here is the ultimate speed of such phase transitions, and to understand how a phase transition evolves in the time domain. Here we apply time-resolved X-ray diffraction to directly measure the changes in long-range order during ultrafast melting of the charge and orbitally ordered phase in a perovskite manganite. We find that although the actual change in crystal symmetry associated with this transition occurs over different timescales characteristic of the many electronic and vibrational coordinates of the system, the dynamics of the phase transformation can be well described using a single time-dependent 'order parameter' that depends exclusively on the electronic excitation. [ABSTRACT FROM AUTHOR]

We have synthesized BaFeOx thin films by pulsed-laser deposition followed by low temperature (200 °C) oxidation to BaFeO3. X-ray diffraction indicates that fully oxidized single crystalline BaFeO3 has been formed with a lattice parameter of 3.97 Å, the bulk stoichiometric value. The oxidation state of Fe is confirmed to be 4+ by using hard x-ray photoemission spectroscopy. A ferromagnetic ground state is found with saturation magnetization and Curie temperature of 3.2 μB/formula unit and 115 K, respectively. Unusually, for a uniform cubic ferromagnet, the films are insulating with an optical gap of ∼1.8 eV. [ABSTRACT FROM AUTHOR]

We describe the design, construction, and performance of a 4-circle in-vacuum diffractometer for resonant elastic soft x-ray scattering. The diffractometer, installed on the resonant elastic and inelastic x-ray scattering beamline at the Canadian Light Source, includes 9 in-vacuum motions driven by in-vacuum stepper motors and operates in ultra-high vacuum at base pressure of 2 × 10-10 Torr. Cooling to a base temperature of 18 K is provided with a closed-cycle cryostat. The diffractometer includes a choice of 3 photon detectors: a photodiode, a channeltron, and a 2D sensitive channelplate detector. Along with variable slit and filter options, these detectors are suitable for studying a wide range of phenomena having both weak and strong diffraction signals. Example measurements of diffraction and reflectivity in Nd-doped (La,Sr)2CuO4 and thin film (Ga,Mn)As are shown. [ABSTRACT FROM AUTHOR]

We have studied the chemical potential shift and changes in the electronic density of states near the Fermi level ( E ) as functions of temperature and carrier concentration in PrCaMnO (PCMO) and NdSrMnO (NSMO) by measurements of photoemission spectra. Suppression of the chemical potential shift as a function of carrier concentration has been observed in PCMO and NSMO near and in the composition range where the CE-type antiferromagnetic charge-ordered (CO) phase appears at low temperatures. This result indicates that there is charge self-organization on a microscopic scale such as stripe formation in this composition range. In the ferromagnetic metallic phase of NSMO, we found a large temperature-dependent chemical potential shift at low temperatures and attributed this to double-exchange mechanism. Suppression of the temperature-dependent chemical potential shift near Curie temperature was observed, possibly associated with the formation of correlated polarons. In the valence band near the E of PCMO, spectral weight was transferred with hole doping, leading to a finite intensity at E even in the paramagnetic insulating phase above the CO phase for x≳0.3, and as the temperature was lowered, a clear gap opening was observed in the CO phase. [ABSTRACT FROM AUTHOR]

Nowadays it has become feasible to perform angle-resolved photoemission spectroscopy (ARPES) measurements of transition-metal oxides with three-dimensional perovskite structures owing to the availability of high-quality single crystals of bulk and epitaxial thin films. In this article, we review recent experimental results and interpretation of ARPES data using empirical tight-binding band-structure calculations. Results are presented for SrVO3 (SVO) bulk single crystals and La1-xSrxFeO3 (LSFO) and La1-xSrxMnO3 (LSMO) thin films. In the case of SVO, from comparison of the experimental results with calculated surface electronic structure, we concluded that the obtained band dispersions reflect the bulk electronic structure. The experimental band structures of LSFO and LSMO were analyzed assuming the G-type antiferromagnetic state and the ferromagnetic state, respectively. We also demonstrated that the intrinsic uncertainty of the electron momentum perpendicular to the crystal surface is important for the interpretation of the APRES results of three-dimensional materials. [ABSTRACT FROM AUTHOR]

Publisher's Note: "Hard x-ray photoemission study on strain effect in LaNiO3 thin films" [Appl. Phys Lett. The citation was added to the lefthand side of page 2, line 11, "...thickness control was investigated in HAXPES. SP 41 sp " References 41 through 58 have been renumbered in text and the reference list. All online and print versions of the article were corrected on 22 April 2021. [Extracted from the article]

X-ray absorption spectroscopy is one of the most widely used experimental techniques to study the electronic and spatial structure of materials. Fluorescence yield mode is bulk-sensitive, but has several serious problems coming from saturation effects. In this study, we show the usefulness of partial fluorescence yields in addressing these problems. We discuss the different behaviors of La2NiMnO6 and LiMnO2 at the Mn 2p absorption edges. The total fluorescence yield produces misleading spectra for LiMnO2 due to the absence of high-Z (Z: atomic number) elements. We conclude that the measurement of the inverse partial fluorescence yield is essential in studies of LiMnO2, which is a hotly debated Li-ion battery material. [ABSTRACT FROM AUTHOR]

Eu doped rare-earth orthovanadates are known to be good red phosphor materials. In particular, LaVO4:Eu is a promising candidate due to the low Eu-site point symmetry, and thus high dipole transition probability within Judd-Ofelt theory. However, the low solubility limit (<3 mol %) of Eu in LaVO4 prevents its efficient use as a phosphor. We present optical evidence of enhanced Eu solubility as high as 10 mol % in LaVO4:Eu thin films grown by pulsed laser deposition and postannealing. The photoluminescent intensity exceeded that of YVO4:Eu thin films when excited below the host bandgap, indicating stronger direct emission of Eu in LaVO4. [ABSTRACT FROM AUTHOR]

We present an x-ray absorption study of the oxidation states of transition-metal-ions of LiMnO2 and its related materials, widely used as cathodes in Li-ion batteries. The comparison between the obtained spectrum and the configuration-interaction cluster-model calculations showed that the Mn3+ in LiMnO2 is a mixture of the high-spin and low-spin states. We found that Li deficiencies occur in the case of Cr substitution, whereas there are no Li deficiencies in the case of Ni substitution. We conclude that the substitution of charge-transfer-type Ni or Cu is effective for LiMnO2 battery materials. [ABSTRACT FROM AUTHOR]

We present an x-ray absorption study of the dependence of the V oxidation state on the thickness of LaVO3 (LVO) and capping LaAlO3 (LAO) layers in the multilayer structure of LVO sandwiched between LAO. We found that the change of the valence of V as a function of LAO layer thickness can be qualitatively explained by a transition between electronically reconstructed interfaces and a chemical reconstruction. The change as a function of LVO layer thickness is complicated by the presence of a considerable amount of V4+ in the bulk of the thicker LVO layers. [ABSTRACT FROM AUTHOR]

Epitaxial Ba0.5Sr0.5TiO3 thin films were prepared on Nb-doped SrTiO3 (100) substrates by the pulsed laser deposition technique and were studied by measuring the Ti 2p→3d resonant photoemission spectra in the valence-band region as a function of film thickness, both at room temperature and low temperature. The results demonstrated an abrupt variation in the spectral structures between 2.8 nm (∼7 ML) and 2.0 nm (∼5 ML) Ba0.5Sr0.5TiO3 films, suggesting that there exists a critical thickness for phase change in the range of 2.0–2.8 nm. This may be ascribed mainly to the intrinsic size effects. [ABSTRACT FROM AUTHOR]

We used x-ray photoemission spectroscopy to investigate the electronic structure of one to five unit cell thick layers of the Mott insulator LaVO3 embedded in LaAlO3. By limiting the upper layer of LaAlO3 to three unit cells, the underlying LaVO3 could be probed. The V 2p core-level spectra had both V3+ and V4+ components, and above two unit cell thick LaVO3, the structures exhibited spectra similar to bulk samples. The atomically flat surfaces enabled the study of the emission angle dependence, which indicates that the V4+ is localized to the topmost layer. These results demonstrate the potential for probing interface electronic structure in oxide ultrathin films by surface spectroscopy. [ABSTRACT FROM AUTHOR]

We have investigated the interfacial electronic structure of La0.6Sr0.4MnO3 (LSMO)/SrTiO3 (STO)/LSMO heterojunctions utilizing the elemental selectivity of photoemission spectroscopy. The Ti 2p core-level spectra clearly show Ti4+ states and do not exhibit any indication of Ti3+ states in TiO2 layers irrespective of a different kind of adjacent atomic layer with different chemical carrier concentration. This result indicates that the Ti ions in the TiO2 atomic layers preserve their tetravalent states even in the vicinity of the valence-mismatched interface between LSMO and STO, reflecting the chemical stability of the Ti4+ states. [ABSTRACT FROM AUTHOR]

We have investigated the Mn 3d spectral function in La0.6Sr0.4FeO3(LSFO)/ La0.6Sr0.4MnO3(LSMO) heterointerfaces as well as of La1-xSrxMnO3 films using Mn 2p-3d resonant photoemission spectroscopy. The strong enhancement of the Mn 3d spectra at the Mn 2p-3d threshold enables us to extract the Mn 3d spectra of LSMO layers in the vicinity of the interface with the LSFO overlayers. We have found that the spectral intensity of eg↑ states near the Fermi level is gradually reduced with increasing LSFO overlayer thickness and is finally saturated at 5–7 ML. The close similarity in reduction of the intensity of the eg↑ states between the LSFO/LSMO interface and hole-doped LSMO films indicates the occurrence of charge transfer at the interface between the LSMO and LSFO layers. [ABSTRACT FROM AUTHOR]

We studied the charge-orbital ordering in the superlattice of charge-ordered insulating Pr0.5Ca0.5MnO3 and ferromagnetic metallic La0.5Sr0.5MnO3 by resonant soft x-ray diffraction (RSXD) and hard x-ray photoemission spectroscopy (HXPES). A temperature-dependent incommensurability is found in the orbital ordering by RSXD. In addition, a large hysteresis is observed that is caused by phase competition between the insulating charge ordered and metallic ferromagnetic states. No magnetic phase transitions are observed in contrast to pure Pr0.5Ca0.5MnO3 thin films, confirming the unique character of the superlattice. Mn HXPES spectra revealed a hysteresis in the metalicity, supporting the picture of phase competition. The deviation from the commensurate orbital order can be directly related to the decrease of ordered-layer thickness that leads to dimensional crossover from three-dimensional to two-dimensional orbital ordering. [ABSTRACT FROM AUTHOR]