Study of Resistive Micromegas in a Mixed Neutron and Photon Radiation Field

The Muon ATLAS Micromegas Activity (MAMMA) focuses on the development and testing of large-area muon detectors based on the bulk-Micromegas technology. These detectors are candidates for the upgrade of the ATLAS Muon System in view of the luminosity upgrade of Large Hadron Collider at CERN (sLHC). They will combine trigger and precision measurement capability in a single device. A novel protection scheme using resistive strips above the readout electrode has been developed. The response and sparking properties of resistive Micromegas detectors were successfully tested in a mixed (neutron and gamma) high radiation field supplied by the Tandem accelerator, at the N.C.S.R. Demokritos in Athens. Monte-Carlo studies have been employed to study the effect of 5.5 MeV neutrons impinging on Micromegas detectors. The response of the Micromegas detectors on the photons originating from the inevitable neutron inelastic scattering on the surrounding materials of the experimental facility was also studied

Off-diagonal magnetoimpedance in field-annealed Co-based amorphous ribbons

The off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons was measured in the low-frequency range using a pick-up coil wound around the sample. The asymmetric two-peak behavior of the field dependence of the off-diagonal impedance was observed. The asymmetry is attributed to the formation of a hard magnetic crystalline phase at the ribbon surface. The experimental results are interpreted in terms of the surface impedance tensor. It is assumed that the ribbon consists of an inner amorphous region and surface crystalline layers. The coupling between the crystalline and amorphous phases is described through an effective bias field. A qualitative agreement between the calculated dependences and experimental data is demonstrated. The results obtained may be useful for development of weak magnetic-field sensors.Comment: 19 pages, 6 figure

Electronic Transport in the Oxygen Deficient Ferromagnetic Semiconducting TiO2−δ_{2-\delta}

TiO$_{2-\delta}$ films were deposited on (100) Lanthanum aluminates LaAlO$_{3}$ substrates at a very low oxygen chamber pressure $P\approx 0.3$ mtorr employing a pulsed laser ablation deposition technique. In previous work, it was established that the oxygen deficiency in these films induced ferromagnetism. In this work it is demonstrated that this same oxygen deficiency also gives rise to semiconductor titanium ion impurity donor energy levels. Transport resistivity measurements in thin films of TiO$_{2-\delta}$ are presented as a function of temperature and magnetic field. Magneto- and Hall- resistivity is explained in terms of electronic excitations from the titanium ion donor levels into the conduction band.Comment: RevTeX4, Four pages, Four Figures in ^.eps forma

Nano granular metallic Fe - oxygen deficient TiO2−δ_{2-\delta} composite films: A room temperature, highly carrier polarized magnetic semiconductor

Nano granular metallic iron (Fe) and titanium dioxide (TiO$_{2-\delta}$) were co-deposited on (100) lanthanum aluminate (LaAlO$_3$) substrates in a low oxygen chamber pressure using a pulsed laser ablation deposition (PLD) technique. The co-deposition of Fe and TiO$_2$ resulted in $\approx$ 10 nm metallic Fe spherical grains suspended within a TiO$_{2-\delta}$ matrix. The films show ferromagnetic behavior with a saturation magnetization of 3100 Gauss at room temperature. Our estimate of the saturation magnetization based on the size and distribution of the Fe spheres agreed well with the measured value. The film composite structure was characterized as p-type magnetic semiconductor at 300 K with a carrier density of the order of $10^{22} /{\rm cm^3}$. The hole carriers were excited at the interface between the nano granular Fe and TiO$_{2-\delta}$ matrix similar to holes excited in the metal/n-type semiconductor interface commonly observed in Metal-Oxide-Semiconductor (MOS) devices. From the large anomalous Hall effect directly observed in these films it follows that the holes at the interface were strongly spin polarized. Structure and magneto transport properties suggested that these PLD films have potential nano spintronics applications.Comment: 6 pages in Latex including 8 figure

Synthesis of easily sinterable ceramic electrolytes based on Bi-doped 8YSZ for IT-SOFC applications

Ceramic electrolytes formed by Bi (4 mol%)-doped 8YSZ, i.e., Y2O3 (8 mol%)-doped ZrO2, were synthesized by a simple co-precipitation route, using ammonia solution as precipitating agent. The amorphous as-synthesized powders convert into zirconia-based single phase with fluorite structure through a mild calcination step at 500 \ub0C. The calcined powders were sintered at very low temperatures (i.e., 900-1100 \ub0C) achieving in both cases very high values of relative densities (i.e., > 95%); the corresponding microstructures were highly homogeneous and characterized by micrometric grains or sub-micrometric grains for sintering at 1100 \ub0C and 900 \ub0C, respectively. Very interesting electrochemical properties were determined by Electrochemical Impedance Spectroscopy (EIS) in the best samples. In particular, their total ionic conductivity, recorded at 650 \ub0C, are 6.06 7 10-2S/cm and 4.44 7 10-2S/cm for Bi (4 mol%)-doped 8YSZ sintered at 1100 \ub0C and 900 \ub0C, respectively. Therefore, Bi was proved to be an excellent sintering aid dopant for YSZ, highly improving its densification at lower temperatures while increasing its total ionic conductivity

Relaxation Mechanism for Ordered Magnetic Materials

We have formulated a relaxation mechanism for ferrites and ferromagnetic metals whereby the coupling between the magnetic motion and lattice is based purely on continuum arguments concerning magnetostriction. This theoretical approach contrasts with previous mechanisms based on microscopic formulations of spin-phonon interactions employing a discrete lattice. Our model explains for the first time the scaling of the intrinsic FMR linewidth with frequency, and 1/M temperature dependence and the anisotropic nature of magnetic relaxation in ordered magnetic materials, where M is the magnetization. Without introducing adjustable parameters our model is in reasonable quantitative agreement with experimental measurements of the intrinsic magnetic resonance linewidths of important class of ordered magnetic materials, insulator or metals

CMB Temperature Polarization Correlation and Primordial Gravitational Waves

We examine the use of the CMB's TE cross correlation power spectrum as a complementary test to detect primordial gravitational waves (PGWs). The first method used is based on the determination of the lowest multipole, $\ell_0$, where the TE power spectrum, $C_{\ell}^{TE}$, first changes sign. The second method uses Wiener filtering on the CMB TE data to remove the density perturbations contribution to the TE power spectrum. In principle this leaves only the contribution of PGWs. We examine two toy experiments (one ideal and another more realistic) to see their ability to constrain PGWs using the TE power spectrum alone. We found that an ideal experiment, one limited only by cosmic variance, can detect PGWs with a ratio of tensor to scalar metric perturbation power spectra $r=0.3$ at 99.9% confidence level using only the TE correlation. This value is comparable with current constraints obtained by WMAP based on the $2\sigma$ upper limits to the B-mode amplitude. We demonstrate that to measure PGWs by their contribution to the TE cross correlation power spectrum in a realistic ground based experiment when real instrumental noise is taken into account, the tensor-to-scalar ratio, $r$, should be approximately three times larger.Comment: 13 pages, 13 figures, version matches published version. Combined with 0710.365