Makoto Kaburagi

Surface structure of MgO(001) surface studied by LEED

MgO(001) surfaces prepared by three different heat treatments were studied by LEED. The first was the surface just after the vacuum cleavage; the second was that after the annealing of the first one at 300°C in UHV. The third was prepared by cleaving in air and heating in oxygen until the carbon Auger peak disappear. LEED I-V curves of the diffraction spots, (10), (11) and (20), were recorded and compared carefully. No remarkable difference corresponding to the preparing methods was found. Therefore, the atomic structures of the surfaces seem to be similar to each other. These experimental I-V curves were compared with the theoretical curves obtained by dynamical calculations for several grades of surface relaxation. The theoretical curves with no relaxation or with the smallest one in the calculation (2.5% expand) fitted best with the experimental curves. The experimental curves were also compared with the theoretical ones calculated for the rumpled surface. But no effect induced by the rumpling was found in the experimental curves.

Ground-State Phase Diagram and Magnetization Curves of the Spin-1 Antiferromagnetic Heisenberg Chain with Bond Alternation and Uniaxial Single-Ion-Type Anisotropy

Ground-state properties of the spin-1 antiferromagnetic Heisenberg chain with bond alternation and uniaxial single-ion-type anisotropy, which is described by the Hamiltonian \({\cal H}_0 = \sum_{\ell=1}^N\{1-(-1)^\ell\alpha\}{\mib S}_\ell\cdot{\mib S}_{\ell+1} + D\sum_{\ell=1}^N\;(S_\ell^z)^2\) (0.0 ≤α≤1.0, -∞< D < ∞), are studied. An exact diagonalization method by means of the Lanczos technique is used. The ground-state phase diagram on the α versus D plane at the thermodynamic limit is determined by analyzing the Binder parameters associated with Neel order and z -direction string order for finite-size ( N = 6, 8, …, 16) chains. It is found that there exists a multicritical point at which the Haldane, Neel, and singlet-dimer phases meet and that the singlet-dimer phase and the large- D phase belong to the same unique phase. The ground-state magnetization curves at the thermodynamic limit for various values of α and D are obtained for the system described by the Hamiltonian, H 0 plus the Zeeman term - H...

The ground state of an S = 1/2 distorted diamond chain - a model of Cu3Cl6(H2O)2·2H8C4SO2

We study the ground state of the model Hamiltonian of the trimerized S = 1/2 quantum Heisenberg chain Cu3Cl6(H2O)22H8C4SO2 in which a non-magnetic ground state was observed recently. This model consists of stacked trimers and has three kinds of coupling constant describing the couplings between spins: the intra-trimer coupling constant J1 and the inter-trimer coupling constants J2 and J3. All of these constants are assumed to be antiferromagnetic. By use of an analytical method and physical considerations, we show that there are three phases on the 2 - 3 plane (2J2 / J1, 3J3 / J1): the dimer phase, the spin-fluid phase and the ferrimagnetic phase. The dimer phase is caused by the frustration effect. In the dimer phase, there exists an excitation gap between the twofold-degenerate ground state and the first excited state, which explains the non-magnetic ground state observed in Cu3Cl6(H2O)22H8C4SO2. We also obtain the phase diagram on the 2 - 3 plane from the numerical diagonalization data for finite systems by use of the Lanczos algorithm.

Magnetic properties of the S = 1/2 distorted diamond chain at T = 0

We explore, at T = 0, the magnetic properties of the S = 1/2 antiferromagnetic distorted diamond chain described by the Hamiltonian = ? j = 1N/3{J 1 (S3j?1 ?S3j +S3j ?S3j+1)+J2S3j+1 ?S3j+2 +J3(S3j?2 ?S3j +S3j ?S3j+2)}?H ? l = 1NS lzwith J1, J2, J3 ? 0, which models well A3Cu3(PO4)4 with A = Ca, Sr, Bi4Cu3V2O14 and azurite Cu3(OH)2(CO3)2. We employ the physical consideration, degenerate perturbation theory, level spectroscopy analysis of the numerical diagonalization data obtained by the Lanczos method and also the density matrix renormalization group (DMRG) method. We investigate the mechanisms of the magnetization plateaux at M = Ms/3 and (2/3)Ms, and also show the precise phase diagrams of the (J2/J1,J3/J1) plane concerned with these magnetization plateaux, where M = ? l = 1NS lz and Ms is the saturation magnetization. We also calculate the magnetization curves and the magnetization phase diagrams by means of the DMRG method.

Ground State Structure of Triangular Lattice Gas Model with up to 3rd Neighbor Interactions

The ground state of the triangular lattice gas model with up to 3rd neighbor interactions is investigated by use of the method of geometrical inequalities. The structure of the ground state at an arbitrary value of the particle density is determined in the full regimes of the interactions. Various ordered structures are obtained. Several examples of systems of adsorbates on the FCC(111) plane, of interstitial atoms in the transition metal carbides and nitrides and of the Ising spins, which may correspond to the present model, are discussed on the basis of the obtained results. A certain amount of information about the interactions in the systems is deduced from the observed ordered structures.

Ordered Structure of Adatoms in the Extended Range Lattice Gas Model

The ordered structure of adatoms is discussed in the light of a theory which determines rigorously the ground state of the extended range lattice gas model. Several examples are discussed to show that an appearance or absence of an ordered structure at a particular density yields informations about the adatom interaction. The intermediate phase which may appear at finite temperatures is discussed briefly.

Ground-state phase diagrams of frustrated spin- S XXZ chains: Chiral ordered phases

The ground-state phase diagram of the frustrated spin-S XXZ chain with the competing nearest- and next-nearest-neighbor antiferromagnetic couplings is studied numerically by using the density-matrix renormalization-group method for the cases of

Reformulation of the path probability method and its application to crystal growth models

S=1/2,

Ground-state magnetization curve of a generalized spin-1/2 ladder

3/2,