Coexistence of localized and itinerant electrons in BaFe2X3 (X = S and Se) revealed by photoemission spectroscopy

We report a photoemission study at room temperature on BaFe2X3 (X = S and Se) and CsFe2Se3 in which two-leg ladders are formed by the Fe sites. The Fe 2p core-level peaks of BaFe2X3 are broad and exhibit two components, indicating that itinerant and localized Fe 3d sites coexist similar to KxFe2-ySe2. The Fe 2p core-level peak of CsFe2Se3 is rather sharp and is accompanied by a charge-transfer satellite. The insulating ground state of CsFe2Se3 can be viewed as a Fe2+ Mott insulator in spite of the formal valence of +2.5. The itinerant versus localized behaviors can be associated with the stability of chalcogen p holes in the two-leg ladder structure.Comment: 5 pages, 5 figures, Accepted in publication for Physical Review

Pressure-induced changes in the magnetic and valence state of EuFe2As2

We present the results of electrical resistivity, ac specific heat, magnetic susceptibility, X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) of the ternary iron arsenide EuFe2As2 single crystal under pressure. Applying pressure leads to a continuous suppression of the antiferromagnetism associated with Fe moments and the antiferromagnetic transition temperature becomes zero in the vicinity of a critical pressure Pc ~2.5-2.7 GPa. Pressure-induced re-entrant superconductivity, which is highly sensitive to the homogeneity of the pressure, only appears in the narrow pressure region in the vicinity of Pc due to the competition between superconductivity and the antiferromagnetic ordering of Eu2+ moments. The antiferromagnetic state of Eu2+ moments changes to the ferromagnetic state above 6 GPa. We also found that the ferromagnetic order is suppressed with further increasing pressure, which is connected with a valence change of Eu ions.Comment: 7 pages, 7 figures, accepted for publication in Phys. Rev.

Orbital-dependent modifications of electronic structure across magneto-structural transition in BaFe2As2

Laser angle-resolved photoemission spectroscopy (ARPES) is employed to investigate the temperature (T) dependence of the electronic structure in BaFe2As2 across the magneto-structural transition at TN ~ 140 K. A drastic transformation in Fermi surface (FS) shape across TN is observed, as expected by first-principles band calculations. Polarization-dependent ARPES and band calculations consistently indicate that the observed FSs at kz ~ pi in the low-T antiferromagnetic (AF) state are dominated by the Fe3dzx orbital, leading to the two-fold electronic structure. These results indicate that magneto-structural transition in BaFe2As2 accompanies orbital-dependent modifications in the electronic structure.Comment: 13 pages, 4 figures. accepted by Physical Review Letter

Dexamethasone-loaded carboxymethylchitosan/poly(amidoamine) dendrimer nanoparticles enhances bone formation in vivo

[Excerpt] Dexamethasone-loaded carboxymethylchitosan/poly(amidoamine) dendrimer nanoparticles, CMC/PAMAM-Dex were successfully synthesized to find applications as a controlled system of relevant molecules in Bone Tissue Engineering. These are aimed at modulatingtheproliferation anddifferentiationofstem cells,both invitro and in vivo. In previous work, we have demonstrated that CMC/ PAMAM-Dex nanoparticles are internalized with high efficiency by different cell types, namely osteoblastic-cells, SaOs-2 and rat bone marrow stromal cells, RBMSCs. The biocompatibility of HA and SPCL scaffolds was also assessed by means of seeding RBMSCs onto the materials and performing a luminescent cell viability assay, after 24 and 72hrs. [...]info:eu-repo/semantics/publishedVersio

Studies of the Anomalous Hall Effect and Magnetic Structure of Nd2Mo2O7 -Test of the Chirality Mechanism-

Neutron scattering studies have been carried out under the magnetic fields H//[0_11] and H//[001] on a single crystal of Nd2Mo2O7, whose Hall resistivity(rhoH) exhibits quite unusual H- and temperature(T)-dependences. Material parameters such as the single ion anisotropies of the Mo- and Nd- moments and exchange coupling constants among the Mo-Mo, Mo-Nd and Nd-Nd moments, have been determined to reproduce various kinds of experimental data taken as a function of H and T. For example, the neutron Bragg intensities, magnetization curves and the magnetic specific heats have been reproduced by the common parameters. By using the magnetic structure reproduced by these parameters, the spin chirality (chi) of Mo spins or the fictitious magnetic flux Phi proportional to chi has been calculated as a function of H and T by using equation chi=, where the bracket means the statistical average. (Note that we do not use the equation chi=x, because the local nature of the chirality should be correctly considered.) Comparing the calculated results with the observed rhoH, we can conclude that the unusual behavior of rH cannot be understood consistently only by the chirality mechanism.Comment: 16 pages, 12 fiures, submitted to J. Phys. Soc. Jp

Spin chirality on a two-dimensional frustrated lattice

The collective behavior of interacting magnetic moments can be strongly influenced by the topology of the underlying lattice. In geometrically frustrated spin systems, interesting chiral correlations may develop that are related to the spin arrangement on triangular plaquettes. We report a study of the spin chirality on a two-dimensional geometrically frustrated lattice. Our new chemical synthesis methods allow us to produce large single crystal samples of KFe3(OH)6(SO4)2, an ideal Kagome lattice antiferromagnet. Combined thermodynamic and neutron scattering measurements reveal that the phase transition to the ordered ground-state is unusual. At low temperatures, application of a magnetic field induces a transition between states with different non-trivial spin-textures.Comment: 7 pages, 4 figure

Topological Nature of Anomalous Hall Effect in Ferromagnet

The anomalous Hall effect in two-dimensional ferromagnets is discussed to be the physical realization of the parity anomaly in (2+1)D, and the band crossing points behave as the topological singularity in the Brillouin zone. This appears as the sharp peaks and the sign changes of the transverse conductance $\sigma_{xy}$ as a function of the Fermi energy and/or the magnetization. The relevance to the experiments including the three dimensional systems is also discussed.Comment: LaTeX 13 pages, 3 figure

Quantum Spin Pump in S=1/2 antiferromagnetic chains -Holonomy of phase operators in sine-Gordon theory-

In this paper, we propose the quantum spin pumping in quantum spin systems where an applied electric field ($E$) and magnetic field ($H$) cause a finite spin gap to its critical ground state. When these systems are subject to alternating electromangetic fields; $(E,H)=(\sin\frac{2\pi t}{T},\cos\frac{2\pi t}{T})$ and travel along the {\it{loop}} $\Gamma_{\rm{loop}}$ which encloses their critical ground state in this $E$-$H$ phase diagram, the locking potential in the sine-Gordon model slides and changes its minimum. As a result, the phase operator acquires $2\pi$ holonomy during one cycle along $\Gamma_{\rm{loop}}$, which means that the quantized spin current has been transported through the bulk systems during this adiabatic process. The relevance to real systems such as Cu-benzoate and ${\rm{Yb}}_4{\rm{As}}_3$ is also discussed.Comment: 10 pages, 5 figures, to be published in J. Phys. Soc. Jpn. 74 (2005) no. 4. Typos corrected in the revised versio