Chin-Wei Wang

Superconductivity in zero-dimensional indium nanoparticles

An In nanoparticle powder was fabricated by employing the thermal evaporation method. Size analysis using x-ray diffraction profiles analysis and atomic force microscopy images indicates an average particle diameter of 36(2)nm and a Gaussian size distribution with a half-width of 3nm. The superconducting critical temperature of the In nanopowder increases slightly to 3.57(3)K, which was found to be extremely insensitive to the applied magnetic field. The critical magnetic field reaches ∼5T, which is a factor of 170 times higher than that of bulk In.

Interplay between the magnetic and electric degrees of freedom in multiferroic Co3TeO6

Neutron diffraction, magnetic susceptibility, specific heat, and dielectric constant measurements of single-crystal Co3TeO6 have been measured to study the interplay between the ferroelectricity and magnetic order. Long-range incommensurate magnetic order develops below T-M1 = 26 K, which is followed by three additional zero-field phase transitions at T-M2 = 19.5 K, T-M3 = 18 K, and T-M4 = 16 K where the incommensurate order changes and commensurate order develops. In magnetic fields up to 14 T we find that the magnetic intensities and incommensurate wave vector are dramatically altered as ferroelectricity develops, with a fifth abrupt transition around 10 T. The overall behavior characterizes Co3TeO6 as a type-II multiferroic.

Spin, charge and lattice couplings in Cu-deficient oxysulphide BiOCu0.94S

The electrical and magnetic properties of slightly Cu-deficient BiOCu(0.94)S are investigated using neutron diffraction, ac magnetic susceptibility, magnetization and electrical resistivity measurements. The Cu spins order in a ferromagnetic arrangement below T(C) = 250 K. An antiferromagnetic component develops below 180 K when the crystalline unit cell experiences a sharp thermal contraction upon cooling, resulting in a canted ferromagnetic spin arrangement at low temperatures. In the magnetically ordered state the electrical transport can be described using three-dimensional variable range hopping conduction. An applied magnetic field can effectively reduce the hopping barrier. Spin-charge couplings are clearly revealed when the resistivity departs from the hopping conduction and begins to increase with increasing temperatures above 250 K where the Cu spins become disordered.

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.

Spin Polarization and Quantum Spins in Au Nanoparticles

The present study focuses on investigating the magnetic properties and the critical particle size for developing sizable spontaneous magnetic moment of bare Au nanoparticles. Seven sets of bare Au nanoparticle assemblies, with diameters from 3.5 to 17.5 nm, were fabricated with the gas condensation method. Line profiles of the X-ray diffraction peaks were used to determine the mean particle diameters and size distributions of the nanoparticle assemblies. The magnetization curves M(Ha) reveal Langevin field profiles. Magnetic hysteresis was clearly revealed in the low field regime even at 300 K. Contributions to the magnetization from different size particles in the nanoparticle assemblies were considered when analyzing the M(Ha) curves. The results show that the maximum particle moment will appear in 2.4 nm Au particles. A similar result of the maximum saturation magnetization appearing in 2.3 nm Au particles is also concluded through analysis of the dependency of the saturation magnetization MP on particle size. The MP(d) curve departs significantly from the 1/d dependence, but can be described by a log-normal function. Magnetization can be barely detected for Au particles larger than 27 nm. Magnetic field induced Zeeman magnetization from the quantum confined Kubo gap opening appears in Au nanoparticles smaller than 9.5 nm in diameter.

Striped magnetic ground state of the kagome lattice in Fe4Si2Sn7O16

We have experimentally identified a new magnetic ground state for the kagome lattice, in the perfectly hexagonal Fe2+ (3d6, S = 2) compound Fe4Si2Sn7O16. Representational symmetry analysis of neutron diffraction data shows that below T_N = 3.5 K, the spins on 2/3 of the magnetic ions order into canted antiferromagnetic chains, separated by the remaining 1/3 which are geometrically frustrated and show no long-range order down to at least T = 0.1 K. Moessbauer spectroscopy confirms that there is no static order on the latter 1/3 of the magnetic ions - i.e., they are in a liquid-like rather than a frozen state - down to at least 1.65 K. A heavily Mn-doped sample Fe1.45Mn2.55Si2Sn7O16 has the same magnetic structure. Although the propagation vector q = (0, 1/2 , 1/2 ) breaks hexagonal symmetry, we see no evidence for magnetostriction in the form of a lattice distortion within the resolution of our data. We discuss the relationship to partially frustrated magnetic order on the pyrochlore lattice of Gd2Ti2O7, and to theoretical models that predict symmetry breaking ground states for perfect kagome lattices.

Suppression of superconductivity by interparticle interactions in Al nanoparticle assembly

We report on the observations of enhanced superconductivity in a very loosely packed 6.8 nm Al nanoparticle assembly and the suppression of superconductivity by interparticle interactions, through ac magnetic susceptibility and magnetization measurements. TC and HC of the 6.8 nm Al particles are, respectively, 1.9 and 77 times higher than that of bulk Al. M(Ha) curves taken below and above TC can all be described by a Langevin profile, showing the existence of a spontaneous magnetic component in superconducting phase. Superconductivity is found to be gradually suppressed by interparticle interactions.

Sodium layer chiral distribution and spin structure of Na

The nature of Na ion distribution, diffusion path, and the spin structure of

_2

P2

Ni

-type Na