Magnetically active vacancy related defects in irradiated GaN layers

We present the studies of magnetic properties of 2 MeV 4He+-irradiated GaN grown by metal-organic chemical-vapor deposition. Particle irradiation allowed controllable introduction of Ga-vacancy in the samples. The magnetic moments with concentrations changing between 4.3...8.3x10^17 cm^-3 showing superparamagnetic blocking at room temperature are observed. The appearance of clear hysteresis curve at T = 5 K with coercive field of about H_C = 270 Oe suggests that the formation of more complex Ga vacancy related defects is promoted with increasing Ga vacancy content. The small concentration of the observed magnetically-active defects with respect to the total Ga- vacancy concentration suggests that the presence of the oxygen/hydrogen-related vacancy complexes is the source of the observed magnetic moments.Comment: 3 pages, 3 figure

Anomalous reversible torque in layered superconducting Bi2Sr2CaCu2x single crystal

Magnetic anisotropy of layered superconducting Bi2Sr2CaCu2O x single crystal was investigated by the torque metlod in the reversible regime. The torque was analyzed in the model taking into account 2D layered structure. Considered model gives the better fit to the data wlen the magnetic fieJd is applied near (a, b) plane. Obtained results establish to 6 x 10 3 value of the superconducting effective mass anisotropy coefficient ε

Compressive Creep Behavior of NEXTEL™ 720/Alumina Ceramic Matrix Composite at 1200°C in Air and in Steam Environment

The aerospace community continues to push the envelope in engineering aircraft that fly higher, faster, and safer while operating with a greater degree of efficiency. To meet these operational requirements innovative aerospace components must be designed to operate in aggressive environments. This research will investigate the ultimate compressive strength and the compressive creep behavior of NextelTM 720/Alumina ceramic matrix composite at 1200 °C in air and 100% steam environments. The effects of creep loading history on the tensile and compressive material behavior will also be examined. The primary strengths of the N720/A composite are its oxide/oxide composition which inherently resists oxidation and a porous matrix which enables crack deflection producing enhanced matrix damage tolerance. Mechanical testing showed a significant decrease in the compressive performance of N720/A when exposed to steam environment. Conversely, N720/A specimens tested in compressive creep in air experienced an increase in compressive performance. SEM analysis showed that densification of the alpha-alumina matrix occurred in both test environments. In air densification sinters the matrix resulting in a strengthening effect. Whereas, in steam environment analysis shows the addition of hydrogen induces hydrothermal softening of the matrix resulting in a significant loss of the compressive performance of N720/A

Magnetic field in Cepheus A as deduced from OH maser polarimetric observations

We present the results of MERLIN polarization mapping of OH masers at 1665 and 1667 MHz towards the Cepheus A star-forming region. The maser emission is spread over a region of 6 arcsec by 10 arcsec, twice the extent previously detected. In contrast to the 22 GHz water masers, the OH masers associated with H II regions show neither clear velocity gradients nor regular structures. We identified ten Zeeman pairs which imply a magnetic field strength along the line-of-sight from -17.3 to +12.7 mG. The magnetic field is organised on the arcsecond scale, pointing towards us in the west and away from us in the east side. The linearly polarized components, detected for the first time, show regularities in the polarization position angles depending on their position. The electric vectors of OH masers observed towards the outer parts of H II regions are consistent with the interstellar magnetic field orientation, while those seen towards the centres of H II regions are parallel to the radio-jets. A Zeeman quartet inside a southern H II region has now been monitored for 25 years; we confirm that the magnetic field decays monotonically over that period.Comment: 10 pages, 6 figures,accepted for publication in MNRA

Spin Waves in the Ferromagnetic Ground State of the Kagome Staircase System Co3V2O8

Inelastic neutron scattering measurements were performed on single crystal Co3V2O8 wherein magnetic cobalt ions reside on distinct spine and cross-tie sites within kagome staircase planes. This system displays a rich magnetic phase diagram which culminates in a ferromagnetic ground state below Tc~6 K. We have studied the low-lying magnetic excitations in this phase within the kagome plane. Despite the complexity of the system at higher temperatures, linear spin-wave theory describes most of the quantitative detail of the inelastic neutron measurements. Our results show two spin-wave branches, the higher energy of which displays finite spin-wave lifetimes well below Tc, and negligible magnetic exchange coupling between Co moments on the spine sites.Comment: 4 pages and 4 figure

Bis{1,2-bis­[bis­(3-meth­oxy­prop­yl)phosphan­yl]ethane-κ2 P,P′}dichlorido­osmium(II)

In the centrosymmetric title compound, [OsCl2(C18H40O4P2)2], the OsII atom adopts a trans-OsCl2P4 geometry, arising from its coordination by two chelating diphosphane ligands and two chloride ions. One of the meth­oxy side chains of the ligand is disordered over two orientations in a 0.700 (6):0.300 (6) ratio