Magnetic ordering and dielectric relaxation in the double perovskite YBaCuFeO5

Using magnetization, dielectric constant, and neutron diffraction measurements on a high quality single crystal of YBaCuFeO₅ (YBCFO), we demonstrate that the crystal shows two antiferromagnetic transitions at [Formula: see text] K and [Formula: see text] K, and displays a giant dielectric constant with a characteristic of the dielectric relaxation at T _N2. It does not show the evidence of the electric polarization for the crystal used for this study. The transition at T _N1 corresponds with a paramagnetic to antiferromagnetic transition with a magnetic propagation vector doubling the unit cell along three crystallographic axes. Upon cooling, at T _N2, the commensurate spin ordering transforms to a spiral magnetic structure with a propagation vector of ([Formula: see text] [Formula: see text] [Formula: see text]), where [Formula: see text], [Formula: see text], and [Formula: see text] are odd, and the incommensurability δ is temperature dependent. Around the transition boundary at T _N2, both commensurate and incommensurate spin ordering coexist.

Mn vacancy defects, grain boundaries, and A-phase stability of helimagnet MnSi

Mn vacancy defect and grain size are shown to modify the magnetic phase diagram of MnSi significantly, especially near the critical regime of A-phase (skyrmion lattice) formation and the helimagnetic phase transition. Crystals grown using controlled nonstoichiometric initial precursors creates both grain boundaries and intrinsic Mn vacancy defect of various levels in MnSi. The results of combined transport, specific heat, and AC spin susceptibility measurements are compared for MnSi single crystal samples of various manganese deficiency levels and grain sizes. The finite-size effect and Mn vacancy level dependent helical phase transition temperature T(c) have been identified and verified. The stability of A-phase in H-T phase space has been examined through AC spin susceptibility data analysis.

Crystal growth and magnetic ordering of Na2Ni2TeO6 with honeycomb layers and Na2Cu2TeO6 with Cu spin dimers

We report on the crystal growth and magnetic property studies of layered Na₂Ni₂TeO₆ and Na₂Cu₂TeO₆. The former has a honeycomb layer composed of NiO₆ octahedra and the latter is composed of paired CuO₄ plaquettes connected through TeO₆ octahedra.

Evidence for dimer crystal melting in the frustrated spin-ladder system BiCu2PO6

In the spin ladder compound BiCu(2)PO(6), there exists a decisive dynamics of spin excitations that we classify and characterize using inelastic light scattering. We observe an interladder singlet bound mode at 24  cm(-1) and two intraladder bound states at 62 and 108  cm(-1) in the leg (bb) and the rung (cc) polarization as well as a broad triplon continuum extending from 36  cm(-1) to 700  cm(-1). Though isolated spin ladder physics can roughly account for the observed excitations at high energies, frustration and interladder interactions need to be considered to fully describe the spectral distribution and scattering selection rules at low and intermediate energies. In addition, we attribute the rich spectrum of singlet bound modes to a melting of a dimer crystal. Our study provides evidence for a Z(2) quantum phase transition from a dimer to a resonating valence bond state driven by singlet fluctuations.

Site occupancy and magnetic properties of pyrochlore-structured AgOs2O6

AgOs(2)O(6) prepared from ion-exchanged superconducting β-pyrochlore KOs(2)O(6) has been shown to be non-superconducting. Synchrotron x-ray structure refinement suggests that AgOs(2)O(6) has the Ag ion mostly occupying the low-symmetry 32e site in the [Formula: see text] space group of proper occupancy, which is different from the original major occupancy at the high-symmetry 8b site for KOs(2)O(6), and similar to non-superconducting Na(1.4)Os(2)O(6)·H(2)O. Magnetic susceptibility measurements found no magnetic ordering down to ~1.7 K. The trace amount of isolated spins suggests that the Ag could be neutral and lead to a pure Os(6+) valence state of zero spin in the newly prepared AgOs(2)O(6).

Scanning transmission electron microscopy using selective high-order laue zones: three-dimensional atomic ordering in sodium cobaltate

A new scanning transmission electron microscopy (STEM) imaging technique using high-order Laue zones (named HOLZ-STEM), a diffraction contrast which has been strenuously avoided or minimized in traditional STEM imaging, can be used to obtain the additional 1D periodic information along the electron propagation axis without sacrificing atomic resolution in the lateral (2D) dimension. HOLZ-STEM has been demonstrated to resolve the 3D long-range Na ordering of Na0.71CoO2. Direct evidence of spiral-like Na-trimer chains twisting along the c axis is unambiguously established in real space.

Sodium ion ordering and vacancy cluster formation in NaxCoO2 (x=0.71 and 0.84) single crystals by synchrotron X-Ray diffraction

In the rich phase diagram of NaxCoO2, x=0.71 enjoys special stability and is called the Curie-Weiss metal due to its anomalous properties. Similarly, x=0.84 prepared from high temperature melt is a special end point beyond which the system phase separates. Using synchrotron x-ray diffraction on single crystals, we discovered sqrt[12]a and sqrt[13]a superlattice structures which we interpret as the ordering of Na (vacancy) clusters. These results lead to a picture of coexisting local moments and itinerant carriers and form the first step towards understanding the many anomalous properties of cobaltates.

Local moment, itinerancy, and deviation from Fermi-liquid behavior in NaxCoO2 for 0.71< or = x < or =0.84

Here we report the observation of Fermi surface (FS) pockets via the Shubnikov-de Haas effect in NaxCoO2 for x=0.71 and 0.84, respectively. Our observations indicate that the FS expected for each compound intersects their corresponding Brillouin zones, as defined by the previously reported superlattice structures, leading to small reconstructed FS pockets, but only if a precise number of holes per unit cell is localized. For 0.71< or = x < 0.75 the coexistence of itinerant carriers and localized S=1/2 spins on a paramagnetic triangular superlattice leads at low temperatures to the observation of a deviation from standard Fermi-liquid behavior in the electrical transport and heat capacity properties, suggesting the formation of some kind of quantum spin-liquid ground state.

59Co NMR evidence for charge ordering below T_(CO) approximately 51 K in Na0.5CoO2

The CoO2 layers in NaxCoO2 may be viewed as a spin S=1/2 triangular-lattice doped with charge carriers. The underlying physics of the cobaltates is very similar to that of the high T_(c) cuprates. We will present unequivocal 59Co NMR evidence that below T_(CO) approximately 51 K, the insulating ground state of the itinerant antiferromagnet Na0.5CoO2 (T_(N) approximately 86 K) is induced by charge ordering.

Myositis ossificans

Myositis ossificans is a fairly common disorder that typically involves progressive heterotropic bone formation. A typical case is discussed in this paper. The radiographic findings in myositis ossificans are relevant in differentiating it from a malignant bone tumor and a benign process. Myositis ossificans can cause impairment to a joint with poor rehabilitative results. Limitation of joint function and little reabsorption of the heterotopic bone formation is common. Most cases are posttraumatically related with the brachialis and the quadricep femoris muscles frequently involved. This is especially true for sport injuries.

Posteroanterior versus anteroposterior lumbar spine radiology

The posteroanterior view of the lumbar spine has important features including radiation protection and image quality; these have been studied by various investigators. Investigators have shown that sensitive tissues receive less radiation dosage in the posteroanterior view of the spine for scoliosis screening and intracranial tomography without altering the image quality. This paper emphasizes the importance of the radiation safety aspect of the posteroanterior view and shows the improvement in shape distortion in the lumbar vertebrae.