Hassan Al-Juwhari | University of Jordan (original) (raw)
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Papers by Hassan Al-Juwhari
Material Science Research India, 2014
Molybdenum-zinc substituted hexaferrites were synthesized by high-energy ball milling and subsequ... more Molybdenum-zinc substituted hexaferrites were synthesized by high-energy ball milling and subsequent sintering at different temperatures (1100, 1200, and 1300° C). The samples sintered at 1100° C exhibited good hard magnetic properties, although a decrease in saturation magnetization from 70.2 emu/g for the unsubstituted sample down to 57 emu/g for the sample with x = 0.3 was observed. The drop in saturation magnetization results mainly from the presence of secondary nonmagnetic oxides. The samples sintered at temperatures ≥1200° C showed an improvement in saturation magnetization, and a sharp drop in coercivith. This behavior was associated with the development of the W-type hexaferrite, the particle growth, and possibly the spin reorientation transition from easy-axis to easy-plane.
In this article we report on the structural and magnetic properties of BaFe 12-4x Mo x Zn 3x O 19... more In this article we report on the structural and magnetic properties of BaFe 12-4x Mo x Zn 3x O 19 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 BaMoO 4 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.
New, blue-emitting phosphors were sought among the family of borosilicates as possible new phosph... more New, blue-emitting phosphors were sought among the family of borosilicates as possible new phosphor
hosts. Ca1xEuxB2Si2O8 with the danburite structure could be synthesized at 800 1C and 140 MPa
pressure under hydrothermal conditions. This host material could be activated by Eu2þ to produce a
blue emitting phosphor with an emission peak close to the desired value of 450 nm, and chromaticity
coordinates close to the published NTSC values for the blue standard.
Material Science Research India, 2014
Molybdenum-zinc substituted hexaferrites were synthesized by high-energy ball milling and subsequ... more Molybdenum-zinc substituted hexaferrites were synthesized by high-energy ball milling and subsequent sintering at different temperatures (1100, 1200, and 1300° C). The samples sintered at 1100° C exhibited good hard magnetic properties, although a decrease in saturation magnetization from 70.2 emu/g for the unsubstituted sample down to 57 emu/g for the sample with x = 0.3 was observed. The drop in saturation magnetization results mainly from the presence of secondary nonmagnetic oxides. The samples sintered at temperatures ≥1200° C showed an improvement in saturation magnetization, and a sharp drop in coercivith. This behavior was associated with the development of the W-type hexaferrite, the particle growth, and possibly the spin reorientation transition from easy-axis to easy-plane.
In this article we report on the structural and magnetic properties of BaFe 12-4x Mo x Zn 3x O 19... more In this article we report on the structural and magnetic properties of BaFe 12-4x Mo x Zn 3x O 19 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 BaMoO 4 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.
New, blue-emitting phosphors were sought among the family of borosilicates as possible new phosph... more New, blue-emitting phosphors were sought among the family of borosilicates as possible new phosphor
hosts. Ca1xEuxB2Si2O8 with the danburite structure could be synthesized at 800 1C and 140 MPa
pressure under hydrothermal conditions. This host material could be activated by Eu2þ to produce a
blue emitting phosphor with an emission peak close to the desired value of 450 nm, and chromaticity
coordinates close to the published NTSC values for the blue standard.