The Experts below are selected from a list of 3012 Experts worldwide ranked by ideXlab platform
Gary J. Long - One of the best experts on this subject based on the ideXlab platform.
-
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...
-
Redox reactions in Prussian blue containing paint layers as a result of light exposure
Journal of Analytical Atomic Spectrometry, 2013Co-Authors: Louise Samain, Fernande Grandjean, Gary J. Long, Bernard Gilbert, David StrivayAbstract:Prussian blue, a mixed valence pigment, typically KFeIII[FeII(CN)6]·xH2O, was the most widely used blue artistic pigment from ca. 1720 to the 1970's but, unfortunately, its paint layers, especially when used in conjunction with a white pigment, tend to fade or turn green upon extended exposure to light. In order to identify the mechanism underlying these changes, paint layers have been prepared with differing amounts of these white pigments and subjected to accelerated light exposure fading. The resulting unfaded and faded paint layers as well as both the Berlin white pigment, Fe2II[FeII(CN)6], and the partially oxidized Berlin green pigment, {KFeIII[FeII(CN)6]}x{FeIII[FeIII(CN)6]}1−x, have been characterized by Raman and Iron-57 Mossbauer Spectroscopy. The results indicate that, upon fading, the Prussian blue pigment painted with a linseed oil binder and (PbCO3)2Pb(OH)2 or ZnO, and to a lesser extent with TiO2, undergoes a reduction at the exposed paint surface and an oxidation in the bulk of the paint layer. This combined reduction and oxidation disrupts, at least in part, the FeIII–N–C–FeII intervalent electron transfer pathways in Prussian blue thus leading to pigment fading through a reduction in the intervalent electron transfer absorbance at about 700 nm.
-
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.
-
Spin-Frustrated Complex, [FeIIFeIII(trans-1,4-cyclohexanedicarboxylate)1.5]∞ : Interplay between Single-Chain Magnetic Behavior and Magnetic Ordering
Inorganic chemistry, 2009Co-Authors: Yan-zhen Zheng, Fernande Grandjean, Gary J. Long, Wei Xue, Wei-xiong Zhang, Ming-liang Tong, Xiao-ming Chen, Pierre Panissod, Marc DrillonAbstract:A three-dimensional mixed-valent iron(II,III) trans-1,4-cyclohexanedicarboxylate, 1,4-chdc, coordination polymer, [FeIIFeIII(μ4-O)(1,4-chdc)1.5]∞, 1, has been synthesized hydrothermally by mixing iron powder and 1,4-chdcH2 and investigated by X-ray diffraction, dc and ac magnetic susceptibility, and Iron-57 Mossbauer Spectroscopy over a wide range of temperatures. Single-crystal X-ray diffraction studies of 1 at 90(2), 293(2), and 473(2) K reveal a tetrahedral [FeII2(μ4-O)FeIII2(μ4-O)]6+ mixed-spin-chain structure with no change in the P1 space group but with subtle changes in the Fe−O and Fe···Fe distances with increasing temperature. These changes are associated with the electron delocalization observed by Mossbauer Spectroscopy above 225 K. Magnetic studies reveal three different magnetic regimes in 1 between 2 and 320 K. Above 36 K 1 is a one-dimensional ferrimagnetic-like complex with frustration arising from competing exchange interactions between the iron(II) and iron(III) ions in the chains. Betw...
-
A structural, magnetic, and Mössbauer spectral study of the TbCo4―xFexB compounds with x=0, 1, and 2
Journal of Applied Physics, 2009Co-Authors: Hervé Mayot, Fernande Grandjean, Olivier Isnard, Gary J. LongAbstract:The TbCo4−xFexB compounds with x=0, 1, and 2 have been investigated by x-ray and neutron diffraction, magnetic measurements, and Iron-57 Mossbauer Spectroscopy. The substitution of cobalt by iron induces both an anisotropic increase in the unit-cell volume and a large increase of approximately 250 K in the Curie temperature; the 4.2 K magnetization decreases continuously with increasing iron content. The powder neutron diffraction patterns and the Mossbauer spectra of the TbCo4−xFexB compounds reveal a strong preferential substitution of iron for cobalt on the 2c site, small transition metal magnetic moments of approximately 1.7μB, and small iron hyperfine fields of approximately 16 T. The compensation temperature of the TbCo4−xFexB compounds decreases continuously from 400 to 350 K between x=0 and 2 as the result of an iron induced increase in the transition metal magnetization. The magnetic moment and hyperfine field are found to be larger on the 2c site than on the 6i site, a difference that reflects t...
Fernande Grandjean - One of the best experts on this subject based on the ideXlab platform.
-
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...
-
Redox reactions in Prussian blue containing paint layers as a result of light exposure
Journal of Analytical Atomic Spectrometry, 2013Co-Authors: Louise Samain, Fernande Grandjean, Gary J. Long, Bernard Gilbert, David StrivayAbstract:Prussian blue, a mixed valence pigment, typically KFeIII[FeII(CN)6]·xH2O, was the most widely used blue artistic pigment from ca. 1720 to the 1970's but, unfortunately, its paint layers, especially when used in conjunction with a white pigment, tend to fade or turn green upon extended exposure to light. In order to identify the mechanism underlying these changes, paint layers have been prepared with differing amounts of these white pigments and subjected to accelerated light exposure fading. The resulting unfaded and faded paint layers as well as both the Berlin white pigment, Fe2II[FeII(CN)6], and the partially oxidized Berlin green pigment, {KFeIII[FeII(CN)6]}x{FeIII[FeIII(CN)6]}1−x, have been characterized by Raman and Iron-57 Mossbauer Spectroscopy. The results indicate that, upon fading, the Prussian blue pigment painted with a linseed oil binder and (PbCO3)2Pb(OH)2 or ZnO, and to a lesser extent with TiO2, undergoes a reduction at the exposed paint surface and an oxidation in the bulk of the paint layer. This combined reduction and oxidation disrupts, at least in part, the FeIII–N–C–FeII intervalent electron transfer pathways in Prussian blue thus leading to pigment fading through a reduction in the intervalent electron transfer absorbance at about 700 nm.
-
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.
-
Spin-Frustrated Complex, [FeIIFeIII(trans-1,4-cyclohexanedicarboxylate)1.5]∞ : Interplay between Single-Chain Magnetic Behavior and Magnetic Ordering
Inorganic chemistry, 2009Co-Authors: Yan-zhen Zheng, Fernande Grandjean, Gary J. Long, Wei Xue, Wei-xiong Zhang, Ming-liang Tong, Xiao-ming Chen, Pierre Panissod, Marc DrillonAbstract:A three-dimensional mixed-valent iron(II,III) trans-1,4-cyclohexanedicarboxylate, 1,4-chdc, coordination polymer, [FeIIFeIII(μ4-O)(1,4-chdc)1.5]∞, 1, has been synthesized hydrothermally by mixing iron powder and 1,4-chdcH2 and investigated by X-ray diffraction, dc and ac magnetic susceptibility, and Iron-57 Mossbauer Spectroscopy over a wide range of temperatures. Single-crystal X-ray diffraction studies of 1 at 90(2), 293(2), and 473(2) K reveal a tetrahedral [FeII2(μ4-O)FeIII2(μ4-O)]6+ mixed-spin-chain structure with no change in the P1 space group but with subtle changes in the Fe−O and Fe···Fe distances with increasing temperature. These changes are associated with the electron delocalization observed by Mossbauer Spectroscopy above 225 K. Magnetic studies reveal three different magnetic regimes in 1 between 2 and 320 K. Above 36 K 1 is a one-dimensional ferrimagnetic-like complex with frustration arising from competing exchange interactions between the iron(II) and iron(III) ions in the chains. Betw...
-
A structural, magnetic, and Mössbauer spectral study of the TbCo4―xFexB compounds with x=0, 1, and 2
Journal of Applied Physics, 2009Co-Authors: Hervé Mayot, Fernande Grandjean, Olivier Isnard, Gary J. LongAbstract:The TbCo4−xFexB compounds with x=0, 1, and 2 have been investigated by x-ray and neutron diffraction, magnetic measurements, and Iron-57 Mossbauer Spectroscopy. The substitution of cobalt by iron induces both an anisotropic increase in the unit-cell volume and a large increase of approximately 250 K in the Curie temperature; the 4.2 K magnetization decreases continuously with increasing iron content. The powder neutron diffraction patterns and the Mossbauer spectra of the TbCo4−xFexB compounds reveal a strong preferential substitution of iron for cobalt on the 2c site, small transition metal magnetic moments of approximately 1.7μB, and small iron hyperfine fields of approximately 16 T. The compensation temperature of the TbCo4−xFexB compounds decreases continuously from 400 to 350 K between x=0 and 2 as the result of an iron induced increase in the transition metal magnetization. The magnetic moment and hyperfine field are found to be larger on the 2c site than on the 6i site, a difference that reflects t...
Olivier Isnard - One of the best experts on this subject based on the ideXlab platform.
-
A structural, magnetic, and Mössbauer spectral study of the TbCo4―xFexB compounds with x=0, 1, and 2
Journal of Applied Physics, 2009Co-Authors: Hervé Mayot, Fernande Grandjean, Olivier Isnard, Gary J. LongAbstract:The TbCo4−xFexB compounds with x=0, 1, and 2 have been investigated by x-ray and neutron diffraction, magnetic measurements, and Iron-57 Mossbauer Spectroscopy. The substitution of cobalt by iron induces both an anisotropic increase in the unit-cell volume and a large increase of approximately 250 K in the Curie temperature; the 4.2 K magnetization decreases continuously with increasing iron content. The powder neutron diffraction patterns and the Mossbauer spectra of the TbCo4−xFexB compounds reveal a strong preferential substitution of iron for cobalt on the 2c site, small transition metal magnetic moments of approximately 1.7μB, and small iron hyperfine fields of approximately 16 T. The compensation temperature of the TbCo4−xFexB compounds decreases continuously from 400 to 350 K between x=0 and 2 as the result of an iron induced increase in the transition metal magnetization. The magnetic moment and hyperfine field are found to be larger on the 2c site than on the 6i site, a difference that reflects t...
-
A structural, magnetic, and Mössbauer spectral study of the DyCo4−xFexB compounds, with x=0–3
Journal of Applied Physics, 2008Co-Authors: Hervé Mayot, Fernande Grandjean, Olivier Isnard, Gary J. LongAbstract:The DyCo4−xFexB compounds, with x=0, 1, 1.5, 2, 2.5, and 3, have been investigated by x-ray diffraction, magnetic measurements, and Iron-57 Mossbauer Spectroscopy. The substitution of cobalt by iron induces both an anisotropic increase in the unit-cell volume and a large increase in the Curie temperature. The 4.2K magnetization decreases with increasing iron content. The Mossbauer spectra of the DyCo4−xFexB compounds with x=1, 1.5, and 2 reveal rather small iron hyperfine fields of approximately 16T and large quadrupole interactions of +1.0 and −1.0mm∕s, for the 6i and 2c sites, respectively. The relative areas of the 6i and 2c spectral components indicate a strong preferential substitution of iron on the 2c site. In DyCo3FeB approximately 70% of the iron occupies the 2c site; a strong increase in the a lattice parameter and in the Curie temperature is observed between DyCo4B and DyCo3FeB and smaller increases are observed for x>1. The compensation temperature of the DyCo4−xFexB compounds decreases from 3...
-
Magnetic and Mössbauer Spectral Evidence for the Suppression of the Magnetic Spin Reorientation in Tm 2 Fe 17 by Deuterium
Physical Review B, 2002Co-Authors: Fernande Grandjean, Olivier Isnard, Gary J. LongAbstract:The structural and magnetic properties of Tm 2 Fe 1 7 and Tm 2 Fe 1 7 D 3 . 2 are investigated by means of x-ray-diffraction, thermal, and ac magnetic susceptibility measurements, and Iron-57 Mossbauer Spectroscopy. Both compounds crystallize in a hexagonal P6 3 /mmc space group with a Th 2 Ni 1 7 -like structure. Deuterium insertion into Tm 2 Fe 1 7 induces large increases in the unit-cell volume, the saturation magnetization, and the ordering temperature. The unit-cell expansion is anisotropic, with a larger increase in the a lattice parameter than the c lattice parameter. A spin reorientation is observed at 90 K in Tm 2 Fe 1 7 in the temperature dependence of both the ac susceptibility and the Mossbauer spectra. Above and below 90 K, the iron magnetic moments are aligned within the basal plane and along the c-axis, respectively. An analysis of the Mossbauer spectra from 4.2 to 320 K yields the orientation of the iron magnetic moments and hyperfine fields, relative to the axes of the electric-field gradient tensor at the iron sites. As revealed by both the ac susceptibility measurements and the Mossbauer spectra, deuterium insertion into Tm 2 Fe 1 7 suppresses this spin reorientation, and in Tm 2 Fe 1 7 D 3 . 2 the iron magnetic moments are oriented within the basal plane of the unit cell from 4.2 to 295 K. The spin reorientation in Tm 2 Fe 1 7 results from a competition between the thulium and iron magnetic anisotropies. Below 90 K the thulium anisotropy dominates and favors an axial alignment of the spins. In contrast to carbon and nitrogen, deuterium insertion into Tm 2 Fe 1 7 decreases the influence of the thulium anisotropy, and in Tm 2 Fe 1 7 D 3 . 2 the iron anisotropy dominates and favors a basal alignment of the magnetic moments.
-
A structural, magnetic, and Mössbauer spectral study of Dy2Fe17 and its hydrides
Journal of Applied Physics, 2000Co-Authors: Olivier Isnard, Gary J. Long, Dimitri Hautot, F. GrandjeanAbstract:The structural and magnetic properties of the Dy2Fe17Hx compounds, where x is 0, 1, 2, 3, and 3.8, have been investigated by means of powder x-ray diffraction, thermomagnetic and ac magnetic susceptibility measurements, and Iron-57 Mossbauer Spectroscopy. The Dy2Fe17Hx compounds crystallize in a hexagonal Th2Ni17 -like structure which has both an iron-rich stoichiometry and disorder of the Dy and Fe–Fe dumbbell sites. The increase in the lattice parameters, the magnetic ordering temperature, the saturation magnetization, and the dependence of the Mossbauer hyperfine parameters upon hydrogen content support a two-step filling by hydrogen of the interstitial sites with hydrogen first filling the octahedral 6h sites for x
F. Grandjean - One of the best experts on this subject based on the ideXlab platform.
-
A structural, magnetic, and Mössbauer spectral study of Dy2Fe17 and its hydrides
Journal of Applied Physics, 2000Co-Authors: Olivier Isnard, Gary J. Long, Dimitri Hautot, F. GrandjeanAbstract:The structural and magnetic properties of the Dy2Fe17Hx compounds, where x is 0, 1, 2, 3, and 3.8, have been investigated by means of powder x-ray diffraction, thermomagnetic and ac magnetic susceptibility measurements, and Iron-57 Mossbauer Spectroscopy. The Dy2Fe17Hx compounds crystallize in a hexagonal Th2Ni17 -like structure which has both an iron-rich stoichiometry and disorder of the Dy and Fe–Fe dumbbell sites. The increase in the lattice parameters, the magnetic ordering temperature, the saturation magnetization, and the dependence of the Mossbauer hyperfine parameters upon hydrogen content support a two-step filling by hydrogen of the interstitial sites with hydrogen first filling the octahedral 6h sites for x
-
Magnetic and Mössbauer spectral properties of the compound Nd6Fe13Au
Journal of Alloys and Compounds, 1996Co-Authors: C.h. De Groot, Gary J. Long, Dimitri Hautot, F.r. De Boer, K.h.j. Buschow, F. GrandjeanAbstract:Abstract The magnetic properties of Nd 6 Fe 13 Au were studied by means of magnetic measurements and Iron-57 Mossbauer Spectroscopy. It is shown that magnetic ordering of the Fe moments occurs at temperatures much above room temperature ( T N = 408 K). At low temperatures, the net moment of Nd 6 Fe 13 Au is very small owing to mutual compensation of the contributions of the various magnetic sublattices involved. High-field measurements made at 4.2 K show that ferromagnetic alignment of the sublattice moments is reached in two steps via first-order magnetic phase transitions. The Mossbauer spectra reveal that the Zeeman splitting gradually decreases with increasing temperature and that the average hyperfine field is zero at 435 K and above. Between 325 K and 411 K the area in the Mossbauer spectra due to the ordered magnetic component decreases gradually as it is replaced by a quadrupole doublet.
Hervé Mayot - One of the best experts on this subject based on the ideXlab platform.
-
A structural, magnetic, and Mössbauer spectral study of the TbCo4―xFexB compounds with x=0, 1, and 2
Journal of Applied Physics, 2009Co-Authors: Hervé Mayot, Fernande Grandjean, Olivier Isnard, Gary J. LongAbstract:The TbCo4−xFexB compounds with x=0, 1, and 2 have been investigated by x-ray and neutron diffraction, magnetic measurements, and Iron-57 Mossbauer Spectroscopy. The substitution of cobalt by iron induces both an anisotropic increase in the unit-cell volume and a large increase of approximately 250 K in the Curie temperature; the 4.2 K magnetization decreases continuously with increasing iron content. The powder neutron diffraction patterns and the Mossbauer spectra of the TbCo4−xFexB compounds reveal a strong preferential substitution of iron for cobalt on the 2c site, small transition metal magnetic moments of approximately 1.7μB, and small iron hyperfine fields of approximately 16 T. The compensation temperature of the TbCo4−xFexB compounds decreases continuously from 400 to 350 K between x=0 and 2 as the result of an iron induced increase in the transition metal magnetization. The magnetic moment and hyperfine field are found to be larger on the 2c site than on the 6i site, a difference that reflects t...
-
A structural, magnetic, and Mössbauer spectral study of the DyCo4−xFexB compounds, with x=0–3
Journal of Applied Physics, 2008Co-Authors: Hervé Mayot, Fernande Grandjean, Olivier Isnard, Gary J. LongAbstract:The DyCo4−xFexB compounds, with x=0, 1, 1.5, 2, 2.5, and 3, have been investigated by x-ray diffraction, magnetic measurements, and Iron-57 Mossbauer Spectroscopy. The substitution of cobalt by iron induces both an anisotropic increase in the unit-cell volume and a large increase in the Curie temperature. The 4.2K magnetization decreases with increasing iron content. The Mossbauer spectra of the DyCo4−xFexB compounds with x=1, 1.5, and 2 reveal rather small iron hyperfine fields of approximately 16T and large quadrupole interactions of +1.0 and −1.0mm∕s, for the 6i and 2c sites, respectively. The relative areas of the 6i and 2c spectral components indicate a strong preferential substitution of iron on the 2c site. In DyCo3FeB approximately 70% of the iron occupies the 2c site; a strong increase in the a lattice parameter and in the Curie temperature is observed between DyCo4B and DyCo3FeB and smaller increases are observed for x>1. The compensation temperature of the DyCo4−xFexB compounds decreases from 3...
