Mufeed Awawdeh

Effects of Heat Treatment on the Phase Evolution, Structural, and Magnetic Properties of Mo-Zn Doped M-Type Hexaferrites

In this article we report on the structural and magnetic properties of BaFe12-4xMoxZn3xO19 hexaferrites with Mo-Zn substitution for Fe ions. The starting materials were commensurate with the BaM stoichiometry, and the Mo:Zn ratio was 1:3. The powder precursors were prepared by high energy ball milling, and subsequently sintered at temperatures from 1100 to 1300° C. The structural analyses indicated that all samples sintered at 1100° C were dominated by a major M-type hexaferrite phase. The relative abundance of the BaMoO4 and Zn-spinel secondary phases increased with increasing the concentration of the substituents, resulting in a decrease of the saturation magnetization from about 67 emu/g (for x = 0.0) to 55 emu/g (for x = 0.3). The coercivity also decreased from 3275 Oe (for x = 0.0) to 900 Oe (for x = 0.3), demonstrating the ability to tune the coercivity to the range useful for magnetic recording by the substitution process. The saturation magnetization improved significantly with sintering at T > 1100° C, and the coercivity decreased significantly, signaling the transformation of the samples to soft magnetic materials. These magnetic changes were due to the high-temperature reaction of the spinel phase with the BaM phase to produce the W-type hexaferrite phase on the one hand, and to the growth of the particles on the other hand. The magnetic phases were further investigated using Mössbauer spectroscopy and thermomagnetic measurements. Our study indicated that the sample with x = 0.2 has the highest saturation magnetization (74 emu/g at sintering temperature of 1300° C) and a tunable coercivity between 2100 Oe and 450 Oe.

Radioactivity concentrations in soil and vegetables from the northern Jordan Rift Valley and the corresponding dose estimates.

The Jordan Rift Valley (JRV) is considered the food bowl of Jordan, especially during the winter season. In this study, soil and vegetable samples collected from greenhouses in the northern JRV were analysed for their radioactive content. The activity concentrations of (238)U, (235)U, (232)Th, (226)Ra, (137)Cs and (40)K in soil were found to be (+/-SD) 33 +/- 12, 2.2 +/- 0.7, 11.2 +/- 3.3, 40.5 +/- 15.5, 3.5 +/- 1.3 and 156.0 +/- 46.6 (Bq kg(-1)), respectively. In vegetables, the activity concentration of (40)K was found in the range of 698-1439 Bq kg(-1), while those of (226)Ra and (228)Ra were found to be in the range of <0.61-2.56 and <0.69-3.35 Bq kg(-1), respectively. Transfer factors for (40)K were found to be high and ranged from 5 to 8, while those for (226)Ra and (228)Ra were found to be from <0.01 to 0.07 and from <0.09 to 0.42, respectively. The calculated external annual effective dose is found to be within the worldwide range.

Modification of the Magnetic Properties of Co2Y Hexaferrites by Divalent and Trivalent Metal Substitutions

The present study is concerned with the fabrication and characterization of Me2Y substituted hexaferrites, Ba2Me2Fe12-xTxO22 (Me = Co2+, Mg2+, and Cr2+, and T = Fe3+, and Ga3+). The samples were prepared by the conventional ball milling technique and sintering at 1200° C. The effect of the choices of Me and T ions on the structural and magnetic properties of the hexaferrites were investigated. XRD patterns, magnetic parameters, and Mössbauer spectra of the Co2Y were consistent with a single phase Y-type hexaferrite. However, the CoCr-Y sample was found to be dominated by the Y-type hexaferrite, and M-type and BaCrO4 minority phases were observed in the XRD pattern of the sample. The small increase in saturation magnetization from about 34 emu/g up to 37.5 emu/g was therefore attributed to the development of the M-type phase. On the other hand, XRD pattern of the Cr2Y sample indicated the dominance of the M-type phase in this sample. The high coercivity (1445 Oe) of this sample is evidence of the transformation of the material from a typically soft magnetic material (Y-type) to a hard magnet (M-type). The Ga-substitution for Fe in Co2Y did not affect the saturation magnetization significantly, but the coercivity was reduced. However, the sample Ba2CoMgFe11GaO22 exhibited a significant reduction of the saturation magnetization down to a value 26.6 emu/g, which could be due to the attenuation of the super-exchange interactions induced by the Mg2+ substitution.

Structural and Mössbauer studies of the alloy system FeAl1−xNbx

X‐ray diffraction and Mossbauer spectroscopy results of the system FeAl1−xNbx show that the cubic (CsCl) FeAl phase dominates for small values of x, and persists as x increases, but also, the hexagonal (C14) Fe2Nb phase develops. The values of the lattice constants and Mossbauer hyperfine parameters indicate that both phases contain impurities, i.e., the phases are FeAl(Nb) and Fe2Nb(Al). The Debye temperature ΘD for the FeAl phase is derived from the intensity analysis of the diffraction lines and a value of (385±5) K is obtained. This is nearly equal to the Debye temperatures for alloys of Fe and Nb. This result is also supported by the fact that the relative Mossbauer absorption intensities corresponding to the two phases remain constant as the temperature is lowered down to 85 K. The absence of magnetic hyperfine splittings in Mossbauer spectra indicate that both phases of the alloy system remain paramagnetic down to the LN2 temperature.