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Frank J. Berry - One of the best experts on this subject based on the ideXlab platform.
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Iron-57 Mössbauer spectroscopic study of fluorinated strontium orthoferrite
Hyperfine Interactions, 2008Co-Authors: Frank J. Berry, Elaine Moore, Xiaolin Ren, Örn Helgason, Michael F. Thomas, S. ShimAbstract:The 57Fe Mossbauer spectra have been recorded at 300 K from an Fe4 + -containing oxygen-deficient perovskite-related SrFeO3 phase and its fluorinated derivative. The fluorinated phase shows complex magnetically split hyperfine patterns reflecting the interactions between Fe3 + ions which are not possible in oxides containing Fe4 + . The 57Fe Mossbauer spectra recorded in situ above 300 K enable the determination of a magnetic ordering temperature of 685 ± 5 K for SrFeO2F.
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Iron 57 mossbauer spectroscopy study of phases in the cazrti2 2xnbxfexo7 zirconolite system
Hyperfine Interactions, 2006Co-Authors: Frank J. Berry, Gordon Oates, Gregory R. Lumpkin, Karl R. WhittleAbstract:Materials of composition CaZrTi2−2x NbxFexO7 with the fluorite-related zirconolite structure have been prepared. The 57Fe Mossbauer spectra show that Iron is initially located in the five co-ordinate cation sites. As the Iron content increases the Iron enters the octahedral sites until, at a composition CaZrTi0.4Nb0.8Fe0.8O7, ca. 50% of the Iron is five co-ordinate and the remainder is located in the octahedral sites.
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Iron-57 Mössbauer spectroscopy study of phases in the CaZrTi2−2xNbxFexO7 zirconolite system
Hyperfine Interactions, 2006Co-Authors: Frank J. Berry, Gordon Oates, Gregory R. Lumpkin, Karl R. WhittleAbstract:Materials of composition CaZrTi2−2x NbxFexO7 with the fluorite-related zirconolite structure have been prepared. The 57Fe Mossbauer spectra show that Iron is initially located in the five co-ordinate cation sites. As the Iron content increases the Iron enters the octahedral sites until, at a composition CaZrTi0.4Nb0.8Fe0.8O7, ca. 50% of the Iron is five co-ordinate and the remainder is located in the octahedral sites.
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Iron-57 Mössbauer Spectroscopic Investigation of Manganese-Doped γ-Fe2O3
Hyperfine Interactions, 2004Co-Authors: Frank J. Berry, Örn Helgason, J. W. Fred MosselmansAbstract:Manganese-doped γ-Fe2O3 has been prepared by precipitation techniques and shown by Mn K-edge XANES and EXAFS to contain Mn3+ in the octahedral sites of the spinel-related structure. The 57Fe Mossbauer spectra recorded in situ between 295 and 750 K show that conversion of the spinel-related γ-Fe2O3 -to the corundum-related α-Fe2O3-structure occurs at ca. 700 and 730 K in the samples containing ca. 1.5 and 4.1% manganese, respectively. The presence of manganese therefore stabilises the γ-Fe2O3-related structure relative to conversion to the α-Fe2O3 phase. The temperature dependence of the spectra recorded from the manganese-doped α-Fe2O3 is similar to that of pure α-Fe2O3 but with a smaller hyperfine magnetic field reflecting the presence of the manganese dopant.
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Iron-57 Mössbauer Spectroscopic Studies of the High Temperature Properties of Metal-Doped Iron Oxides
Hyperfine Interactions, 2002Co-Authors: Ibrar Ayub, Frank J. Berry, Örn HelgasonAbstract:57Fe Mossbauer spectra recorded in situ in vacuo from chromium- and gallium-doped Fe3O4 at elevated temperatures show the dopant ions to depress the Curie temperature of Fe3O4 by ca. 70 K. Spectra recorded from aluminium-doped γ-Fe2O3 show the onset of conversion to aluminium-doped α-Fe2O3 to begin at ca. 750 K, which is ca. 100 K above the conversion temperature for undoped γ-Fe2O3. The variation in magnetic hyperfine fields at temperatures exceeding ca. 750 K is similar to that recorded from α-Fe2O3 when doped with zinc or magnesium. At temperatures exceeding 900 K the zinc doped α-Fe2O3 partially converts to spinel-related ZnFe2O4.
Shuxian Zhu - One of the best experts on this subject based on the ideXlab platform.
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Investigation of conductivity in the Sr(Fe1−xTix)Oy system by Iron-57 Mössbauer spectroscopy
Hyperfine Interactions, 1990Co-Authors: Yufang Zheng, Yan Zhuang, Shuxian ZhuAbstract:On the basis of our previous work electrical conductivity in the Sr(Fe1−xTix)Oy system (0.0≤x≤0.9,y≤3) has been further studied by means of Mossbauer spectroscopy. When 0.0≤x≤0.6, the concentration of Fe3+ (II) doublet relates to the final firing temperature and electrical conductivity of the materials is sensitive to the concentration of Fe3+ (II). Atx=0.25, the curve of the resistivity versus Ti contentx shows a local minimum which is observed for the first time. The results indicate that the coexistence of Fe4+ and Fe3+ in the same lattice leads to high conductivity; the conductivity increases when the Fe4 concentration approaches to that of the Fe3+ one. When the temperature is at 260 K and 230 K, the presence of the intermediate state showing quadrupole splitting has an effect on the conductivity of the materials.
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investigation of conductivity in the sr fe1 xtix oy system by Iron 57 mossbauer spectroscopy
Hyperfine Interactions, 1990Co-Authors: Yufang Zheng, Yan Zhuang, Shuxian ZhuAbstract:On the basis of our previous work electrical conductivity in the Sr(Fe1−xTix)Oy system (0.0≤x≤0.9,y≤3) has been further studied by means of Mossbauer spectroscopy. When 0.0≤x≤0.6, the concentration of Fe3+ (II) doublet relates to the final firing temperature and electrical conductivity of the materials is sensitive to the concentration of Fe3+ (II). Atx=0.25, the curve of the resistivity versus Ti contentx shows a local minimum which is observed for the first time. The results indicate that the coexistence of Fe4+ and Fe3+ in the same lattice leads to high conductivity; the conductivity increases when the Fe4 concentration approaches to that of the Fe3+ one. When the temperature is at 260 K and 230 K, the presence of the intermediate state showing quadrupole splitting has an effect on the conductivity of the materials.
Fernande Grandjean - One of the best experts on this subject based on the ideXlab platform.
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Comment on "Calibration of 57Fe Mössbauer constants by first principles" Phys. Chem. Chem. Phys., 2016, 18, 10201-10206.
Physical Chemistry Chemical Physics, 2016Co-Authors: Fernande Grandjean, Gary J. LongAbstract:The proportionality constant, α, between the observed isomer shifts and the calculated electron probability density at the Iron nucleus has been reevaluated in terms of the correct experimental isomer shifts relative to α-Iron and their corresponding accuracy, which should be considered in the linear regression fit yielding α. The Iron-57 excited state nuclear quadrupole moment, Q, is not a "relative" value and its widely accepted experimental value is 0.16(1) × 10-28 m2 as also confirmed by nuclear model calculations.
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Mössbauer spectroscopy as a probe of magnetization dynamics in the linear Iron(I) and Iron(II) complexes [Fe(C(SiMe3)3)2](1-/0.).
Inorganic Chemistry, 2013Co-Authors: Joseph M. Zadrozny, Fernande Grandjean, Dianne J. Xiao, Jeffrey R. Long, Mihail Atanasov, Frank Neese, Gary J. LongAbstract:The Iron-57 Mossbauer spectra of the linear, two-coordinate complexes, [K(crypt-222)][Fe(C(SiMe3)3)2], 1, and Fe(C(SiMe3)3)2, 2, were measured between 5 and 295 K under zero applied direct current (dc) field. These spectra were analyzed with a relaxation profile that models the relaxation of the hyperfine field associated with the inversion of the Iron cation spin. Because of the lifetime of the measurement (10–8 to 10–9 s), Iron-57 Mossbauer spectroscopy yielded the magnetization dynamics of 1 and 2 on a significantly faster time scale than was previously possible with alternating current (ac) magnetometry. From the modeling of the Mossbauer spectral profiles, Arrhenius plots between 5 and 295 K were obtained for both 1 and 2. The high-temperature regimes revealed Orbach relaxation processes with Ueff = 246(3) and 178(9) cm–1 for 1 and 2, respectively, effective relaxation barriers which are in agreement with magnetic measurements and supporting ab initio calculations. In 1, two distinct high-temperature...
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The Mössbauer Effect and its Application to Hard Permanent Magnetic Materials
ChemInform, 2010Co-Authors: Gary J. Long, Fernande GrandjeanAbstract:The complex room temperature Mossbauer spectra of Y2Fe14B and Nd2Fe14B, [1] shown in Figure 1, may seem rather ominous to the reader who is not familiar with the technique of Mossbauer spectroscopy. However, this complexity contains much useful information about the structural and magnetic properties of these materials. This chapter, which will show how this useful information may be extracted from such complex spectra, will introduce the basic principles of Iron-57 Mossbauer spectroscopy and will stress the resolution achieved with this isotope. Then it will discuss the fundamental hyperfine parameters as measured by Mossbauer spectroscopy in rather more simple materials than Y2Fe14B and Nd2Fe14B. A latter section will cover the computer analysis techniques which may be used to extract the maximum amount of information from complex spectra such as those shown in Figure 1. Finally, the last section will review the application of Iron-57 Mossbauer spectroscopy to the R2Fe14B hard permanent magnetic materials. Pertinent studies with other Mossbauer isotopes will also be discussed.
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A Mossbauer spectral study of the GdCo4-xFexB compounds
Journal of Applied Physics, 2007Co-Authors: Fernande Grandjean, Raphaël P. Hermann, Eustachy S. Popiel, Gary J. LongAbstract:The Iron-57 Mossbauer spectra of the GdCo4−xFexB compounds, where x is 0.10, 0.15, 0.20, 0.25, 1, 2, 2.5, and 2.6, have been measured at room temperature and reveal relatively small Iron hyperfine fields of approximately 12–18T, relatively large quadrupole interactions of approximately +0.9 and −1mm∕s, and three very different types of spectra for x=0.10 and 0.15, x=0.25, 1, and 2, and x=2.5 and 2.6. The differences result from both the different easy magnetization directions in these compounds and the different cobalt and∕or Iron occupancies of the crystallographic 2c and 6i sites. The spectra have been fitted by calculating the spectral absorption with the complete Iron-57 nuclear excited state Hamiltonian for the Iron 2c and 6i sites. The fits have used an asymmetry parameter η and Euler angles θ and ϕ that relate the hyperfine field to the Iron electric field gradient axes of each crystallographic site in an orientation that is consistent with the structural and magnetic properties of the site. The re...
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An Iron-57 and tin-119 Mössbauer spectral study of NdMn6−xFexSn6
Journal of Physics: Condensed Matter, 2005Co-Authors: Fernande Grandjean, Gary J. Long, Bernard Mahieu, J. Han, William Joseph JamesAbstract:The Iron-57 Mossbauer spectra of the NdMn6-xFexSn6 compounds with x = 0.5, 1.0, 1.5 and 2.0 have been obtained at 4.2, 78 and 295 K, and the tin-119 Mossbauer spectra of the NdMn6-xFexSn6 compounds with x = 0.0, 0.5, 1.0, 1.5 and 2.0 have been obtained between 85 and 370 K. A successful and rational analysis of the spectra is based upon a Wigner-Seitz cell analysis of the HoFe6Sn6-structure with the Immm space group for NdMn6Sn6 and of the TbFe6Sn6-structure with the Cmcm space group for the NdMn6-xFexSn6 compounds with x = 0.5, 1.0, 1.5 and 2.0. Both the Iron-57 and the tin-119 spectra reveal that the spin reorientation exhibited by these compounds at low temperature is extremely sensitive to the cooling rate of the samples. Specifically, samples that are slowly cooled from 295 to 78 K retain their 295 K magnetic structure and do not exhibit a spin reorientation. In contrast, samples that are quenched from 295 to 78 K and then further cooled to 4.2 K exhibit a spin reorientation. The ca 15 T Iron-57 hyperfine fields observed at 4.2 K are unusually small, whereas the ca 25 T tin-119 transferred hyperfine fields observed at 85 K are unusually large. These latter large fields, as well as the improvement in Curie temperature and magnetization with increasing Iron content in the NdMn6-xFexSn6 compounds, are discussed in terms of earlier electronic structure calculations.
Gary J. Long - One of the best experts on this subject based on the ideXlab platform.
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Comment on "Calibration of 57Fe Mössbauer constants by first principles" Phys. Chem. Chem. Phys., 2016, 18, 10201-10206.
Physical Chemistry Chemical Physics, 2016Co-Authors: Fernande Grandjean, Gary J. LongAbstract:The proportionality constant, α, between the observed isomer shifts and the calculated electron probability density at the Iron nucleus has been reevaluated in terms of the correct experimental isomer shifts relative to α-Iron and their corresponding accuracy, which should be considered in the linear regression fit yielding α. The Iron-57 excited state nuclear quadrupole moment, Q, is not a "relative" value and its widely accepted experimental value is 0.16(1) × 10-28 m2 as also confirmed by nuclear model calculations.
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Mössbauer spectroscopy as a probe of magnetization dynamics in the linear Iron(I) and Iron(II) complexes [Fe(C(SiMe3)3)2](1-/0.).
Inorganic Chemistry, 2013Co-Authors: Joseph M. Zadrozny, Fernande Grandjean, Dianne J. Xiao, Jeffrey R. Long, Mihail Atanasov, Frank Neese, Gary J. LongAbstract:The Iron-57 Mossbauer spectra of the linear, two-coordinate complexes, [K(crypt-222)][Fe(C(SiMe3)3)2], 1, and Fe(C(SiMe3)3)2, 2, were measured between 5 and 295 K under zero applied direct current (dc) field. These spectra were analyzed with a relaxation profile that models the relaxation of the hyperfine field associated with the inversion of the Iron cation spin. Because of the lifetime of the measurement (10–8 to 10–9 s), Iron-57 Mossbauer spectroscopy yielded the magnetization dynamics of 1 and 2 on a significantly faster time scale than was previously possible with alternating current (ac) magnetometry. From the modeling of the Mossbauer spectral profiles, Arrhenius plots between 5 and 295 K were obtained for both 1 and 2. The high-temperature regimes revealed Orbach relaxation processes with Ueff = 246(3) and 178(9) cm–1 for 1 and 2, respectively, effective relaxation barriers which are in agreement with magnetic measurements and supporting ab initio calculations. In 1, two distinct high-temperature...
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The Mössbauer Effect and its Application to Hard Permanent Magnetic Materials
ChemInform, 2010Co-Authors: Gary J. Long, Fernande GrandjeanAbstract:The complex room temperature Mossbauer spectra of Y2Fe14B and Nd2Fe14B, [1] shown in Figure 1, may seem rather ominous to the reader who is not familiar with the technique of Mossbauer spectroscopy. However, this complexity contains much useful information about the structural and magnetic properties of these materials. This chapter, which will show how this useful information may be extracted from such complex spectra, will introduce the basic principles of Iron-57 Mossbauer spectroscopy and will stress the resolution achieved with this isotope. Then it will discuss the fundamental hyperfine parameters as measured by Mossbauer spectroscopy in rather more simple materials than Y2Fe14B and Nd2Fe14B. A latter section will cover the computer analysis techniques which may be used to extract the maximum amount of information from complex spectra such as those shown in Figure 1. Finally, the last section will review the application of Iron-57 Mossbauer spectroscopy to the R2Fe14B hard permanent magnetic materials. Pertinent studies with other Mossbauer isotopes will also be discussed.
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A Mossbauer spectral study of the GdCo4-xFexB compounds
Journal of Applied Physics, 2007Co-Authors: Fernande Grandjean, Raphaël P. Hermann, Eustachy S. Popiel, Gary J. LongAbstract:The Iron-57 Mossbauer spectra of the GdCo4−xFexB compounds, where x is 0.10, 0.15, 0.20, 0.25, 1, 2, 2.5, and 2.6, have been measured at room temperature and reveal relatively small Iron hyperfine fields of approximately 12–18T, relatively large quadrupole interactions of approximately +0.9 and −1mm∕s, and three very different types of spectra for x=0.10 and 0.15, x=0.25, 1, and 2, and x=2.5 and 2.6. The differences result from both the different easy magnetization directions in these compounds and the different cobalt and∕or Iron occupancies of the crystallographic 2c and 6i sites. The spectra have been fitted by calculating the spectral absorption with the complete Iron-57 nuclear excited state Hamiltonian for the Iron 2c and 6i sites. The fits have used an asymmetry parameter η and Euler angles θ and ϕ that relate the hyperfine field to the Iron electric field gradient axes of each crystallographic site in an orientation that is consistent with the structural and magnetic properties of the site. The re...
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An Iron-57 and tin-119 Mössbauer spectral study of NdMn6−xFexSn6
Journal of Physics: Condensed Matter, 2005Co-Authors: Fernande Grandjean, Gary J. Long, Bernard Mahieu, J. Han, William Joseph JamesAbstract:The Iron-57 Mossbauer spectra of the NdMn6-xFexSn6 compounds with x = 0.5, 1.0, 1.5 and 2.0 have been obtained at 4.2, 78 and 295 K, and the tin-119 Mossbauer spectra of the NdMn6-xFexSn6 compounds with x = 0.0, 0.5, 1.0, 1.5 and 2.0 have been obtained between 85 and 370 K. A successful and rational analysis of the spectra is based upon a Wigner-Seitz cell analysis of the HoFe6Sn6-structure with the Immm space group for NdMn6Sn6 and of the TbFe6Sn6-structure with the Cmcm space group for the NdMn6-xFexSn6 compounds with x = 0.5, 1.0, 1.5 and 2.0. Both the Iron-57 and the tin-119 spectra reveal that the spin reorientation exhibited by these compounds at low temperature is extremely sensitive to the cooling rate of the samples. Specifically, samples that are slowly cooled from 295 to 78 K retain their 295 K magnetic structure and do not exhibit a spin reorientation. In contrast, samples that are quenched from 295 to 78 K and then further cooled to 4.2 K exhibit a spin reorientation. The ca 15 T Iron-57 hyperfine fields observed at 4.2 K are unusually small, whereas the ca 25 T tin-119 transferred hyperfine fields observed at 85 K are unusually large. These latter large fields, as well as the improvement in Curie temperature and magnetization with increasing Iron content in the NdMn6-xFexSn6 compounds, are discussed in terms of earlier electronic structure calculations.
Yufang Zheng - One of the best experts on this subject based on the ideXlab platform.
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Investigation of conductivity in the Sr(Fe1−xTix)Oy system by Iron-57 Mössbauer spectroscopy
Hyperfine Interactions, 1990Co-Authors: Yufang Zheng, Yan Zhuang, Shuxian ZhuAbstract:On the basis of our previous work electrical conductivity in the Sr(Fe1−xTix)Oy system (0.0≤x≤0.9,y≤3) has been further studied by means of Mossbauer spectroscopy. When 0.0≤x≤0.6, the concentration of Fe3+ (II) doublet relates to the final firing temperature and electrical conductivity of the materials is sensitive to the concentration of Fe3+ (II). Atx=0.25, the curve of the resistivity versus Ti contentx shows a local minimum which is observed for the first time. The results indicate that the coexistence of Fe4+ and Fe3+ in the same lattice leads to high conductivity; the conductivity increases when the Fe4 concentration approaches to that of the Fe3+ one. When the temperature is at 260 K and 230 K, the presence of the intermediate state showing quadrupole splitting has an effect on the conductivity of the materials.
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investigation of conductivity in the sr fe1 xtix oy system by Iron 57 mossbauer spectroscopy
Hyperfine Interactions, 1990Co-Authors: Yufang Zheng, Yan Zhuang, Shuxian ZhuAbstract:On the basis of our previous work electrical conductivity in the Sr(Fe1−xTix)Oy system (0.0≤x≤0.9,y≤3) has been further studied by means of Mossbauer spectroscopy. When 0.0≤x≤0.6, the concentration of Fe3+ (II) doublet relates to the final firing temperature and electrical conductivity of the materials is sensitive to the concentration of Fe3+ (II). Atx=0.25, the curve of the resistivity versus Ti contentx shows a local minimum which is observed for the first time. The results indicate that the coexistence of Fe4+ and Fe3+ in the same lattice leads to high conductivity; the conductivity increases when the Fe4 concentration approaches to that of the Fe3+ one. When the temperature is at 260 K and 230 K, the presence of the intermediate state showing quadrupole splitting has an effect on the conductivity of the materials.