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Existence of collective effects in magnetic coupling in ionic solids is studied by mapping spin eigenstates of the Heisenberg and exact nonrelativistic Hamiltonians on cluster models representing KNiF3, K2NiF4, NiO, and La2CuO4. Ab initio techniques are used to estimate the Heisenberg constant J. For clusters with two magnetic centers, the values obtained are about the same for models having more magnetic centers. The absence of collective effects in J strongly suggests that magnetic interactions in this kind of ionic solids are genuinely local and entangle only the two magnetic centers involved.

We discuss the possible mechanisms responsible for ferromagnetic ordering in transition metal oxides and the interplay between electrical transport and magnetic order. We emphasize the role of orbital degrees of freedom, electron correlation effects, local lattice distortions and the oxygen 2p bands in high oxidation state TM oxides. For illustration of the physics we discuss several specific materials like Eu chalcogenides, magnetic semiconductors, La manganates and CrO2 among others. (C) 1997 Elsevier Science Ltd.

We discuss the possible mechanisms responsible for ferromagnetic ordering in transition metal oxides and the interplay between electrical transport and magnetic order. We emphasize the role of orbital degrees of freedom, electron correlation effects, local lattice distortions and the oxygen 2p bands in high oxidation state TM oxides. For illustration of the physics we discuss several specific materials like Eu chalcogenides, magnetic semiconductors, La manganates and CrO2 among others. (C) 1997 Elsevier Science Ltd.

An X-ray photoelectron spectroscopy study of Na-doped Bi-2212 cuprates is reported. Core level photoemission spectra were collected, at different take-off angles, from a monophasic crystal. The results of the lineshape analysis and the dependence of the core line intensity on the analyser take-off angle allowed us to rule out the presence of Na within the Bi-O layers, indicating that Na+ is very likely replacing Ca2+ or Si2+ ions.

We present inhomogeneous Hartree-Fock pins RPA calculations of the optical absorption in La2Cu(4+y). We obtain good agreement with experiment with a LDA parameter set and show also results with an optimized parameter set that fits the observed optical bands. The midinfrared band is explained in terms of renormalized p-d transitions related to Zhang-Rice singlet states. By comparing optical properties with other experiments we can draw a scenario for the occurrence of anomalous Fermi liquid behavior in optimally doped samples.

A contribution to superexchange coming from empty oxygen orbitals is pointed out. We also estimate the small anisotropy of the in-plane superexchange, as well as the superexchange between two adjacent layers in the specific YBa 2 Cu 3 O 6 compound. In doped compounds, we improve the description of the transport properties of Zhang-Rice singlets over the simple t-J model. Particularly important for the bandwidth is the role of what we call t ′ unequal spins and t '' unequal spins . When more than one doped hole is present in the system, the interaction between holes becomes rapidly non-negligible: two Zhang-Rice singlets placed on neighboring cells highly repel each other. Some aspects of oxygen spin dynamics are discussed, in connection with NMR experiments.

The effects of electron-lattice coupling in a multiband Hubbard model are investigated by exact diagonalization. For a system with one doped hole, and with parameters relevant to cuprate superconductors, we find a continuous transition from a delocalized to a small polaron state at a critical value of the electron-phonon interaction. We characterize this state as a Zhang-Rice singlet with distortions in the CuO4 cluster. We find, in addition, a polaronic shift of the band near the Fermi level in the spectral function of the system. An enhancement of the transfer of the low-energy spectral weight is also observed. These results are in qualitative agreement with different spectroscopic measurements for high-T(c) superconductors.

We have studied the three-band Peierls-Hubbard model describing the Cu-O layers in high-T(c) superconductors by using Lanczos diagonalization and assuming infinite mass for the ions. When the system is doped with one hole, and for lambda (the electron-lattice coupling strength) greater than a critical value, we found that the oxygens around one Cu contract and the hole self-traps forming a lattice and electronic small polaron. The self-trapped hole forms a local singlet analogous to the Zhang-Rice singlet in the undeformed lattice. We also studied the single-particle spectral function and the optical conductivity. We have found that the spectral weight, in general, is similar to that found in previous studies where the coupling with the lattice was absent. There is an anomalous transfer of spectral weight but, contrary to those studies, the spectral weight goes to these localized polaronic states. However, this polaronic shift does not seem enough by itself to explain pinning of the chemical potential observed in real materials. The peaks in the optical conductivity are also shifted, according to the polaronic shift, in the single-particle spectral functions. We compare our results to those obtained in inhomogeneous Hartree-Fock calculations and we discuss their relation with experiments.

Calculations of Cu 2p photoelectron spectra for a ${\mathrm{Cu}}_{3}$${\mathrm{O}}_{10}$ cluster with a reduced basis set show that the introduction of more Cu sites leads to a revised interpretation of the Cu 2p spectrum. Besides the usual peaks of mainly 3${\mathit{d}}^{9}$ and 3${\mathit{d}}^{10}$L character another peak appears at lower binding energy. This peak is of mainly 3${\mathit{d}}^{10}$ character. The hole has moved away from the core hole potential and has formed a Zhang-Rice singlet on a neighboring ${\mathrm{CuO}}_{4}$ unit. This effect explains the asymmetric line shape of the main line in the Cu 2p spectra of CuO and the high-${\mathit{T}}_{\mathit{c}}$ compounds. For formally trivalent copper compounds, such as ${\mathrm{NaCuO}}_{2}$, this effect disappears and a narrow line shape is observed. The consequences of hole doping (33%) on the Cu 2p spectra have also been studied. The peak assignment turns out to be very similar to that of the undoped system.

A cell-perturbation method is developed for CuO2 planes in the cuprate superconductors described by a d-p model. It is shown that a single-band t-t'-J-J' model accurately describes the low-energy physics and how the parameters of this model vary with those of the underlying d-p model. The method is similar in spirit to Anderson's original treatment of superexchange [Phys. Rev. 115, 2 (1959)], where the exchange interaction is obtained in second order rather than given by the usual fourth-order result of ordinary perturbation theory (a poor approximation). It is shown that O-O hopping can appreciably affect the absolute and relative magnitudes of the effective single-band parameters and that a regime with J approximately t is quite conceivable. Although triplet (intermediate) states can appreciably enhance the magnitude of the "diagonal" effective hopping t', an effective single-band description should remain valid for all reasonable estimates of the underlying d-p parameters. Correction terms involving hole pairs on neighboring cells are derived and shown to be small. For the "undoped" case, an estimate is made of the critical charge-transfer energy for an insulator-metal transition.

In this paper we present calculation of the photo- and inverse photoemission spectra, and the O 1s and Cu 2p core-level spectra for the high-T(c) materials, using a multiband Hubbard Hamiltonian. The spectra are obtained for small clusters containing two Cu atoms (Cu2O7 and Cu2O8) for the undoped, electron-doped, and hole-doped cases. In order to investigate the sensitivity of the spectra to cluster size and localized versus delocalized oxygen levels, a comparison is made with a (K-dependent) impurity approach and results from a CuO4 cluster. Special attention is paid to the doping dependence of the spectra and low-energy states and to the redistribution of spectral weights upon doping.

1 Introduction and Literature Review||2 Methodology||3 Size Controlled Synthesis of La2CuO4 and SrTiO3 Nanoparticles by Sol-Gel Technique||4 Size Dependent Magnetic Properties of La2CuO4 Nanoparticles Synthesized by Sol-Gel Method||5 Assembly and Electrical Properties of La2CuO4 and SrTiO3 Nanoparticles Based on Dielectrophoresis for Future Electronic Device Applications||6 The Effect of Particle Size on Magnetic Properties of La1.80Sr0.2CuO4 Nanoparticles Fabricated by Sol-Gel Method||7 Weak Ferromagnetism in La2CuO4-y Nanoparticles||8 Conclusions and Suggestions, Investigation of magnetism and electrical properties of nano-sized particles has been a subject of interest in past years owing that their properties are deviated compared to their bulk. Perovskite oxide is one of the best materials to study such effect, since lattice distortion and non-stoichiometric form is allowed in the structure, depending on various stimuli, thus the material is potentially to appear with extraordinary variety of properties. For example, modulating electrical properties from insulating to metallic is possible. Therefore, investigation of a perovskite oxide in nanoscale order is become important. La2CuO4 (LCO) and SrTiO3 (STO) nanoparticles (NPs) were selected in this research work. LCO is basically a frontier of strong correlated materials of an antiferromagnetic (AF) Mott insulator. The strong electron-electron interactions makes the material to exhibit superconductivity, by introducing charge carriers to the system. As an AF and metal oxide, the LCO also potentially to have various applications such as spin-valve device and gas sensors, respectively. Moreover, STO also holds important electronic properties owing to its wide band gap, and, since it is an excellent substrate for epitaxial growth, physics of oxide heterostructure based on STO material is also of interest to be studied. To date, there are no details report on the magnetic and electric properties on free-standing STO and LCO. By controlling the properties of such nano-sized system, the results obtained will become fundamental for further research work and very potential to be developed for future electronic and magnetic device applications. In the present work, free-standing LCO and STO NPs were synthesized by sol-gel method and its magnetic and/or electric properties were reported. Various method have been applied to synthesize a perovskite, such solid-state, co-precipitation, sol-gel, hydrothermal and spray technique. Sol-gel was selected considering the products are finer, higher in purity, more controllable and easy to conduct. Morphological observation by field emission scanning electron microscopy (FESEM) showed that the NPs has spherical structure and their size could be controlled depending on the annealing condition during synthesis, the size product is proportional with annealing temperature/time of synthesis. X-ray diffractometry (XRD) results indicating the minimum annealing condition to obtain LCO and STO phase at least at 600℃ for 45 min and 500℃ for 5 h, respectively. Additionally, the obtained smallest NPs have 69 nm and 21 nm size, for LCO and STO, respectively. Size dependent magnetic properties of LCO based compound was investigated by superconducting quantum interference device (SQUID) magnetometer, as a function of temperature and magnetic field. Magnetization enhancement was observed with reducing size. Additionally, the magnetism of LCO also was assessed in microscopic view by muon spin rotation (μSR) and the results showed drastically reduction of Néel temperature (TN) with decreasing size. The LCO NPs with 69 nm size has TN at about 60 K, compared to their bulk TN ≈ 300 K. Size effect also studied in the doped sample, the LCO is doped by Sr to exhibit superconductivity. Cancellation of superconductivity was observed in small particle size. Electric properties of the fabricated LCO and STO NPs were also investigated. Firstly, electrodes separated with nanoscale gap were fabricated by electron beam lithography (EBL). The synthesized STO and LCO NPs were aligned at the electrodes by dielectrophoresis (DEP) technique. DEP is a technique to manipulate the movement of particles by applying non-uniform electric field, therefore the NPs bridging electrodes and electrical characteristics can be measured at various temperature. The results showed that the conductance of the samples increases with raising temperature, for both LCO and STO NPs samples. Two conduction mechanisms originating from hopping and tunneling appeared in the Arrhenius plot., 九州工業大学博士学位論文 学位記番号：生工博甲第330号 学位授与年月日：平成30年12月26日, 平成30年度

We have measured the resonant inelastic x-ray scattering (RIXS) spectra at the Cu L-3 edge in a variety of cuprates. Exploiting a considerably improved energy resolution (0.8 eV) we recorded significant dependencies on the sample composition and orientation, on the scattering geometry, and on the incident photon polarization. The RIXS final states correspond to two families of electronic excitations, having local (dd excitations) and nonlocal (charge-transfer) character. The dd energy splitting can be estimated with a simple crystal field model. The RIXS at the L-3 edge demonstrates here a great potential, thanks to the resonance strength and to the large 2p spin-orbit splitting.

High-resolution neutron scattering experiments on optimally doped La2-xSrxCuO4 (x=0.16) reveal that the magnetic excitations are dispersive. The dispersion is the same as in YBa2Cu3O6.85, and is quantitatively related to that observed with charge sensitive probes. The associated velocity in La2-xSrxCuO4 is only weakly dependent on doping with a value close to the spin-wave velocity of the insulating (x=0) parent compound. In contrast with the insulator, the excitations broaden rapidly with increasing energy, forming a continuum at higher energy and bear a remarkable resemblance to multiparticle excitations observed in 1D S=1/2 antiferromagnets. The magnetic correlations are 2D, and so rule out the simplest scenarios where the copper oxide planes are subdivided into weakly interacting 1D magnets.

The magnetic excitation spectrum in the two-dimensional (2D) S = 1/2 Heisenberg antiferromagnet copper deuteroformate tetradeuterate has been measured for temperatures up to T similar to J/2, where J = 6.31 +/- 0.02 meV is the 2D exchange coupling. For T << J, a dispersion of the zone boundary energy is observed, which is attributed to a wave vector dependent quantum renormalization. At higher temperatures, spin-wavelike excitations persist, but are found to broaden and soften. By combining our data with numerical calculations, and with existing theoretical work, a consistent description of the behavior of the model system is found over the whole temperature interval investigated.

The temperature dependence of the structure factor S(k) of the instantaneous magnetic fluctuations in copper formate tetradeuterate has been investigated using neutron scattering techniques. Our data extend to unprecedently high temperatures (T similar to J) compared to the 2D exchange coupling. The correlation length xi and amplitude S-0 are in good agreement with the predictions for a 2D S = 1/2 Heisenberg antiferromagnet on a square lattice.

The effect of band dispersion on the Cu 2 p X-ray photoemission core line in cuprates is studied and a discussion is proposed on the interplay between the local aspects of the photoemission event and the long-range properties of the solid. The Cu 2 p 3/2 core line emission of CuGeO 3 and Bi 2 Sr 2 CaCu 2 O 8 calculated using a parametrized configuration interaction impurity cluster model is compared with the experimental data. It is shown that by explicitly including into the model the valence band density of states, the fine structure of the Cu 2 p 3/2 main line can be reproduced and the main line width increases with the Cu 3 d band dispersion.