K.A. Azez

Mössbauer and structural studies of Fe0.7−xVxAl0.3 alloys

Abstract We report the Mossbauer and structural studies of the alloy system Fe 0.7− x V x Al 0.3 where x =0, 0.02, 0.06, 0.1, 0.2, and 0.3. X-ray diffraction indicates that all the samples studied have single phase with body center cubic structure. The lattice parameter ( a ) increases with increasing the vanadium concentration. Room temperature Mossbauer studies show magnetic ordering for small values of x and paramagnetic behavior for large values of x . The Mossbauer spectra were fitted by a distribution of magnetic hyperfine fields for small values of x and two singlets were added for large values of x . The relation between the hyperfine field and the isomer shift in the hyperfine field distribution is linear. The average hyperfine field and isomer shift were found to decrease with increasing V concentration. The results are interpreted in terms of local environmental effects on the hyperfine interactions.

Mossbauer spectroscopic and crystal structure investigation of the Fe0.7-xTixAl0.3 alloy system

Abstract We describe a combination of Mossbauer spectroscopic and X-ray structural studies on the alloy system Fe0.7−xTixAl0.3 where x=0, 0.05, 0.1, 0.2, 0.3 and 0.35. The dependence of the Mossbauer hyperfine parameters and the lattice constant on x are determined, and a comparison is made to the known behavior of metallic Fe–Al–T alloys. X-ray diffraction patterns indicate that all the samples are single phase with body center cubic structure. The lattice constant increases linearly with increasing Ti concentration. Room temperature Mossbauer studies show magnetic ordering for small x and paramagnetic behavior for large x. The Mossbauer spectra were fitted by a distribution of magnetic hyperfine fields for small x and two singlets were added for large x. Analysis of the X-ray and Mossbauer results show that the Ti atoms preferentially occupy the Fe site. The average hyperfine field and isomer shift decreased with increasing Ti concentration. The results are related to local environment effects on the hyperfine interactions.

Effect of γ-irradiation on polycrystalline Tl1Ba2Ca2Cu3Oy superconductor

Specimens of polycrystalline T1 1 Ba 2 Ca 2 Cu 3 O y superconductor (T1-1223) have been irradiated at room temperature by γ-rays. The variations of the normal state resistance, transition width and the critical current densities with γ-irradiation up to about 400 MR were studied. The normal state resistivity ρ(T) increases gradually up to a dose of 100 MR, whereas at higher doses, the effect of irradiation becomes rather negligible. The transition temperature T c decreases slightly and the transition temperature width AT broadens at doses below 100 MR with almost no change at higher doses up to 400 MR. At relatively low temperatures and low γ-doses, the critical current densities J c (T) increase with γ-irradiation, while the effect of γ-irradiation at temperatures very close to T c is rather negligible. Obtained results confirmed the high sensitivity of (T1-1223) superconductor to γ-irradiation at relatively low γ-doses. These results are discussed and explained in terms of the effect of γ-rays on the weak links and Josephson junctions between the grains.

Effect of gamma irradiation on the transport critical current density of Tl2Ba2Ca2Cu3O10 tapes

Specimens of Tl2Ba2Ca2Cu3O10 tapes were prepared using the powder in tube method. The voltage-current (V - I ) characteristics were used to study the temperature and magnetic field dependence of the critical current density Jc(T,B). Obtained results confirmed the high sensitivity of the superconducting tape to the applied magnetic field and are explained based on the weak links and Josephson junctions between the grains. The temperature dependence of Jc was also derived and discussed in terms of the thermally activated flux flow (TAFF). The effect of gamma irradiation on the critical current density Jc(T,B) was also studied up to a gamma dose of 400 MR. Gamma irradiation was found to increase Jc at relatively low temperature and magnetic field ranges. Therefore, gamma irradiation is a useful method to improve the superconductivity of the Tl2Ba2Ca2Cu3O10 tapes.

Effect of Mn concentration on the spin glass transition temperature of Fe0.70-xMnxAl0.30 alloys

Magnetization measurements on zero field cooled (ZFC) and field cooled (FC) samples as a function of temperature where made on Fe0.70−xMnxAl0.30 alloys with 0≤x≤0.10. Our data show the existence of two regimes of the spin glass temperature Tf when increasing the concentration x of the Mn atoms. We found that Tf decreases slowly with increasing x up to x=0.06 and then shows a rapid linear decrease above this concentration. The existence of two regimes of Tf behavior with x may be attributed to the disappearance of ferromagnetic clusters which exist for low values of x (x 0.06) is associated with more influence of x on Tf.

The rotational magnetic process and effects of gamma-irradiation on vortex flux pinning in Tl-2223 at low temperatures

Magnetization vector measurements were carried out in a polycrystalline sample of Tl-2223 superconductor in fixed fields at low temperatures. Demonstrating the broad distribution in the vortex flux pinning, the vortex flux density B was seen to consist of two component: the rotational component BR turns rigidly with sample rotation and the frictional component BF stays at fixed angle F relative to the applied field H. The pinning torques per vortex were calculated as a function of H at constant temperature. The -irradiated sample shows an increase in pinning torque of ratio seven to one at temperatures 4.2 K and 25 K compared to an unirradiated sample; this is due to defects induced by the gamma irradiation.