The investigations of the crystal and magnetic structures of the BaFe12_xAlxO19 （x = 0.1-1.2） solid solutions have been performed with powder neutron diffractometry. Magnetic properties of the BaFe12_xAlxOt9 （x = 0...The investigations of the crystal and magnetic structures of the BaFe12_xAlxO19 （x = 0.1-1.2） solid solutions have been performed with powder neutron diffractometry. Magnetic properties of the BaFe12_xAlxOt9 （x = 0.1-1.2） solid solutions have been measured by vibration sample magnetometry at different temperatures under different magnetic fields. The atomic coordinates and lattice parameters have been Rietveld refined. The invar effect is observed in low temperature range （from 4.2 K to 150 K）. It is explained by the thermal oscillation anharmonicity of atoms. The increase of microstress with decreasing temperature is found from Rietveld refinement. The Curie temperature and the change of total magnetic moment per formula unit are found for all compositions of the BaFet2_xAlxO19 （x = 0.1-1.2） solid solutions. The magnetic structure model is proposed. The most likely reasons and the mechanism of magnetic structure formation are discussed.展开更多
Barium hexaferrites doped with Er3+, Ba1-xErxFe12O19, x=0.0, 0.01, 0.02, 0.04, 0.06, were prepared by the conventional ceramic technology. The structure and electromagnetic properties of the calcined samples were stud...Barium hexaferrites doped with Er3+, Ba1-xErxFe12O19, x=0.0, 0.01, 0.02, 0.04, 0.06, were prepared by the conventional ceramic technology. The structure and electromagnetic properties of the calcined samples were studied using powder X-ray diffraction (XRD) and network analyzer (Agilent 8722ET). All the XRD patterns showed the single phase of the magnetoplumbite barium ferrite without other intermediate phase when x is below 0.02. The lattice parameters of ferrites doped with Er3+ decreased, indicating that the substitution of Er3+ occurs on Ba2+ basis site and results in a contract of the crystal cell. The microwave electromagnetic properties of the samples have been studied at the frequency range from 2 to 18 GHz. It was shown that ε′ increased slightly, and the maximum of ε″ appeared at low frequency position with Er3+ doping. μ″ and μ′ were improved significantly when x=0.01, and the maxima are 2 and 1.7, respectively. The reasons were also discussed using electromagnetic theory.展开更多
Thin films of barium hexaferrite were prepared on fly ash cenosphere particles by the sol-gel method using Fe（ NO3 ）3 ·9H2O, Ba（ NO3 ）2 and citric acid as raw materials. The prepared films were characterized ...Thin films of barium hexaferrite were prepared on fly ash cenosphere particles by the sol-gel method using Fe（ NO3 ）3 ·9H2O, Ba（ NO3 ）2 and citric acid as raw materials. The prepared films were characterized by differential thermal and thermogravimetric analysis （DTA-TG）, X-ray diffraction analysis （XRD）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDX）, X-ray photoelectron spectroscopy （XPS）, and vibrating sample magnetometry . The magnetic and structural properties of barium hexaferrite coated cenosphere particles were also studied. The experimental results show that even and continual barium hexaferrite coatings were prepared on fly ash cenospheres , and the magnetic conductivity was imparted to these non-conducting oxide ceramic particles. The low density barium hexaferrite coated cenosphere particles may be atilized for manufacturing microwave absorbing materials.展开更多
Barium hexaferrites BaFe11.6Mox Zn0.4-x O19（x=0.1,0.2,0.4）were prepared by precipitation of the precursors using wet chemical mixture method and then sintering the dried powders at 1100℃.The properties of the prepa...Barium hexaferrites BaFe11.6Mox Zn0.4-x O19（x=0.1,0.2,0.4）were prepared by precipitation of the precursors using wet chemical mixture method and then sintering the dried powders at 1100℃.The properties of the prepared samples were investigated using X-ray difraction（XRD）,scanning electron microscopy（SEM）,vibrating sample magnetometer,and Mssbauer spectroscopy.XRD patterns revealed that all prepared samples had BaFe12O19hexaferrite structure as a majority phase.SEM images demonstated that the samples consisted mainly of hexagonal platelet-like grains with diameters ranging from 100 to 500 nm.Mssbauer spectra revealed that Zn2＋ions occupy 4f1 sites leading to the splitting of the 12k component.However Mo6＋ions occupy 2b sites while Mo4＋ prefer 4f1 and 12k sites.For the sample with x=0.4,Mo6＋and Mo4＋ ions were found to have preference for 2b and 12k sites,respectively,and to induce the development of Fe2＋ions in the hexaferrite,leading to noticeable changes in the magnetic properties of the system.The observed magnetic properties were found to be consistent with the preferential site occupation of metal ions,and the hyperfine fields derived from Mssbauer spectra of these samples.展开更多
In the present work, fine barium ferrite powder has been synthesized through a one-step hydrothermal process in an autoclave at [OH-]/[Cl-] ratio of 2:1 in the temperature range from 180 to 260 oC using barium chlorid...In the present work, fine barium ferrite powder has been synthesized through a one-step hydrothermal process in an autoclave at [OH-]/[Cl-] ratio of 2:1 in the temperature range from 180 to 260 oC using barium chloride (BaCl2), ferrous chloride (FeCl2) and potassium nitrate (KNO3) as the starting materials. Both particle size and saturation magnetization (Ms) increase with increasing hydrothermal reaction temperature, while the intrinsic coercivity (iHc) peaks at 685 Oe at 230 oC. Morphology progress from the barium ferrite precursor particles to the barium hexaferrite particles has been monitored with increasing hydrothermal reaction time at 230 oC in the autoclave.展开更多
基金supported by the Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST“MISiS”(Grant No.K4-2015-040)
文摘The investigations of the crystal and magnetic structures of the BaFe12_xAlxO19 （x = 0.1-1.2） solid solutions have been performed with powder neutron diffractometry. Magnetic properties of the BaFe12_xAlxOt9 （x = 0.1-1.2） solid solutions have been measured by vibration sample magnetometry at different temperatures under different magnetic fields. The atomic coordinates and lattice parameters have been Rietveld refined. The invar effect is observed in low temperature range （from 4.2 K to 150 K）. It is explained by the thermal oscillation anharmonicity of atoms. The increase of microstress with decreasing temperature is found from Rietveld refinement. The Curie temperature and the change of total magnetic moment per formula unit are found for all compositions of the BaFet2_xAlxO19 （x = 0.1-1.2） solid solutions. The magnetic structure model is proposed. The most likely reasons and the mechanism of magnetic structure formation are discussed.
基金the National Defence Fundamental Research Project and the Doctor Innovation Fund of NJUT(BSCX200603)
文摘Barium hexaferrites doped with Er3+, Ba1-xErxFe12O19, x=0.0, 0.01, 0.02, 0.04, 0.06, were prepared by the conventional ceramic technology. The structure and electromagnetic properties of the calcined samples were studied using powder X-ray diffraction (XRD) and network analyzer (Agilent 8722ET). All the XRD patterns showed the single phase of the magnetoplumbite barium ferrite without other intermediate phase when x is below 0.02. The lattice parameters of ferrites doped with Er3+ decreased, indicating that the substitution of Er3+ occurs on Ba2+ basis site and results in a contract of the crystal cell. The microwave electromagnetic properties of the samples have been studied at the frequency range from 2 to 18 GHz. It was shown that ε′ increased slightly, and the maximum of ε″ appeared at low frequency position with Er3+ doping. μ″ and μ′ were improved significantly when x=0.01, and the maxima are 2 and 1.7, respectively. The reasons were also discussed using electromagnetic theory.
基金Funded by Hunan Provincial Natural Science Foundation of China(No.04JJ3035) and Scientific Research Fund of Hunan ProvincialEducation Department (No.03B002)
文摘Thin films of barium hexaferrite were prepared on fly ash cenosphere particles by the sol-gel method using Fe（ NO3 ）3 ·9H2O, Ba（ NO3 ）2 and citric acid as raw materials. The prepared films were characterized by differential thermal and thermogravimetric analysis （DTA-TG）, X-ray diffraction analysis （XRD）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDX）, X-ray photoelectron spectroscopy （XPS）, and vibrating sample magnetometry . The magnetic and structural properties of barium hexaferrite coated cenosphere particles were also studied. The experimental results show that even and continual barium hexaferrite coatings were prepared on fly ash cenospheres , and the magnetic conductivity was imparted to these non-conducting oxide ceramic particles. The low density barium hexaferrite coated cenosphere particles may be atilized for manufacturing microwave absorbing materials.
基金supported by a generous grant from the Scientific Research Fund (SRF) in Jordan under grant number(S/1/21/2009)support of the German Academic Exchange Program(DAAD)the Deanship of Scientific research at the University of Jordan under contract number 1404 are also acknowledged
文摘Barium hexaferrites BaFe11.6Mox Zn0.4-x O19（x=0.1,0.2,0.4）were prepared by precipitation of the precursors using wet chemical mixture method and then sintering the dried powders at 1100℃.The properties of the prepared samples were investigated using X-ray difraction（XRD）,scanning electron microscopy（SEM）,vibrating sample magnetometer,and Mssbauer spectroscopy.XRD patterns revealed that all prepared samples had BaFe12O19hexaferrite structure as a majority phase.SEM images demonstated that the samples consisted mainly of hexagonal platelet-like grains with diameters ranging from 100 to 500 nm.Mssbauer spectra revealed that Zn2＋ions occupy 4f1 sites leading to the splitting of the 12k component.However Mo6＋ions occupy 2b sites while Mo4＋ prefer 4f1 and 12k sites.For the sample with x=0.4,Mo6＋and Mo4＋ ions were found to have preference for 2b and 12k sites,respectively,and to induce the development of Fe2＋ions in the hexaferrite,leading to noticeable changes in the magnetic properties of the system.The observed magnetic properties were found to be consistent with the preferential site occupation of metal ions,and the hyperfine fields derived from Mssbauer spectra of these samples.
文摘In the present work, fine barium ferrite powder has been synthesized through a one-step hydrothermal process in an autoclave at [OH-]/[Cl-] ratio of 2:1 in the temperature range from 180 to 260 oC using barium chloride (BaCl2), ferrous chloride (FeCl2) and potassium nitrate (KNO3) as the starting materials. Both particle size and saturation magnetization (Ms) increase with increasing hydrothermal reaction temperature, while the intrinsic coercivity (iHc) peaks at 685 Oe at 230 oC. Morphology progress from the barium ferrite precursor particles to the barium hexaferrite particles has been monitored with increasing hydrothermal reaction time at 230 oC in the autoclave.
