Density-functional-theory (DFT) computations on a Prussian blue analogue (PBA), nickel hexacyanof... more Density-functional-theory (DFT) computations on a Prussian blue analogue (PBA), nickel hexacyanoferrate, Ni2+ 3[Fe3+(CN)6]2·nH2O, predict the existence of a tetragonal (P 4 m2) crystal structure that is energetically degenerate with the previously reported cubic (F 43m) structure for this PBA. The proposed tetragonal structure satisfies observations, such as X-ray diffraction and magnetic measurements, that have been reported previously. A van der Waals corrected exchange-correlation functional is used in the DFT+U computations for an improved description of hydrogen bonding. The results provide strong support for a revised and simplified crystallographic description of Ni2+ 3[Fe3+(CN)6]2·nH2O, and show how H2O molecules stabilize the crystal structure and affect its magnetic and electronic properties. The symmetry lowering in nickel hexacyanoferrate is attributed to the hydration shell of the interstitial nickel cation. Calculations strongly suggest a maximum of n = 7 interstitial ...
Some recent papers [2],[3] report that the nonlinear susceptibility does not depend on quantum si... more Some recent papers [2],[3] report that the nonlinear susceptibility does not depend on quantum size effects. We show that this is not valid when considering the enchancement factor of one particle. Quantum size effects in nanoparticles not only exist but they have dominant contriubution. Our results in good agreement with the model proposed by Rautian [1].
We report the single crystal neutron diffraction studies done to resolve the room-temperature str... more We report the single crystal neutron diffraction studies done to resolve the room-temperature structure of Uranium antimonide, UNi0.5Sb2. The time-of-flight single-crystal neutron diffraction experiments at room temperature were done on the Single Crystal Diffractometer, SCD, at Los Alamos Neutron Science Center. Previous X-ray single crystal and neutron powder diffraction studies could not unambiguously resolve the structure because of the presence
We report on the dependence of the interatomic distances in the intermetallic compound UPdSn as d... more We report on the dependence of the interatomic distances in the intermetallic compound UPdSn as determined from the neutron diffraction data done on HIPD at Los Alamos spallation neutron source. The U-U distance gives a measure of the direct 5f-5f overlap. The U-Pd and U-Sn distances give a measure of 5f-ligand hybridization. Using the Rietveld refinement method, we were able
The UCu4+xAl8-x family crystallizes in the tetragonal ThMn12 - type structure in the range from 0... more The UCu4+xAl8-x family crystallizes in the tetragonal ThMn12 - type structure in the range from 0.1<= x<= 1.95. It has been reported that the Cu-poor compounds show antiferromagnetic long-range order, followed by a transition at x=1.15 to a heavy fermion behavior. We report on the results of thermal conductivity and the Seebeck coefficient as a function of temperature (1.8-300K). Thermal
UPdSn orders antiferromagnetically below 40K and undergoes a second antiferromagnetic transition ... more UPdSn orders antiferromagnetically below 40K and undergoes a second antiferromagnetic transition at about 27 K which has been attributed to spin reorientation. The magnetic properties of UPdSn are highly anisotropic with the c-axis as the hard magnetization direction. For magnetic fields applied in the basal plane, previous studies have observed significant domain repopulation effects as well as a spin-flop transition
We have performed RF skin depth measurements of selected uranium compounds in applied magnetic fi... more We have performed RF skin depth measurements of selected uranium compounds in applied magnetic fields up to 50 T. This technique is relatively new, as applied to metallic samples but is a useful probe of magnetotransport since the skin depth can be simply related to the magnetoresistance.
Examples of UNiAlD2.1 and UCoGe illustrate that the soft crystallographic direction coincides qui... more Examples of UNiAlD2.1 and UCoGe illustrate that the soft crystallographic direction coincides quite generally with the shortest U-U links in U intermetallics. It leads to a simple rule, that the easy magnetization direction and the soft crystallographic direction (in the sense of highest compressibility under hydrostatic pressure) must be mutually orthogonal.
The magnetic structure of two natural samples of goethite (α-FeOOH) with varying crystallinity wa... more The magnetic structure of two natural samples of goethite (α-FeOOH) with varying crystallinity was analyzed at 15 and 300 K by neutron diffraction. The well crystallized sample has thePb′nmcolor space group and remained antiferromagnetic up to 300 K, with spins aligned parallel to thecaxis. The purely magnetic 100 peak, identifying this color space group, was clearly resolved. The nanocrystalline sample shows a phase transition to the paramagnetic state at a temperature below 300 K. This lowering of the Néel temperature may be explained by the interaction of magnetic clusters within particles. The nuclear structure, refined with the Rietveld and pair distribution function methods, is consistent with reports in the literature.
... 10:30 AM–11:54 AM, Saturday, October 18, 2008. Union East, 3rd Floor Room: Wiggins Chair: Mig... more ... 10:30 AM–11:54 AM, Saturday, October 18, 2008. Union East, 3rd Floor Room: Wiggins Chair: Miguel Castro-Colin, The University of Texas at El Paso Abstract ID: BAPS.2008.TS4CF.H6.2. Abstract: H6.00002 : Evolution of Magnetism in Sr$_{2-x}$La$_{x}$FeO$_{4 }$ system of ...
The UTX intermetallic compounds, where T is the transition metal and X is p-electron element, wer... more The UTX intermetallic compounds, where T is the transition metal and X is p-electron element, were found to crystallize mainly in two large groups, the orthorhombic CeCu2 type of structure and the hexagonal ZrAlNi type of structure. In both groups of compounds, bulk and neutron-diffraction measurements have revealed a large variety of magnetic ordering phenomena depending on the degree of the 5f-ligand hybridization. The 5f-ligand hybridization is very sensitive to the overlap of the respective wavefunctions, which can be effectively controlled by external pressure. Applied pressure can be expected to increase the 5f-ligand hybridization. We have summarized existing and new pressure studies of the ordering temperatures and the critical fields of various antiferromagnetic UTX compounds (T = Ni, Co, Ir; X = Al, Ga, Ge) by means of magnetoresistance studies in magnetic fields up to 18 T. The studies were performed on single crystals under hydrostatic pressure up to 10 kbar. The observe...
ABSTRACT Yb3Ga7Ge3 and YbGa4Ge2 were obtained from reactions of Yb and Ge in excess liquid galliu... more ABSTRACT Yb3Ga7Ge3 and YbGa4Ge2 were obtained from reactions of Yb and Ge in excess liquid gallium. The crystal structure of Yb3Ga7Ge3 was refined using X-ray and neutron diffraction data on selected single crystals. Yb3Ga7Ge3 crystallizes in the monoclinic space group C2/c with lattice constants a=12.2261(20) Å, b=10.7447(20) Å, c=8.4754(17) Å and β=110.288(30)° (neutron diffraction data). The crystal structure of Yb3Ga7Ge3 is an intergrowth of planar layers of YbGaxGey and puckered layers of (Ge)n. YbGa4Ge2 crystallizes in a modified PuGa6 structure type in the tetragonal polar space group I4cm with lattice constants a=b=5.9874(6) Å and c=15.1178(19) Å. The structure of YbGa4Ge2 is an intergrowth of puckered Ga layers and puckered GaxGey layers with Yb atoms residing within the channels formed by the connection of the two layers. Physical properties, resistivity (ρ), magnetic susceptibility (χ) and specific heat (C) were measured for Yb3Ga7Ge3. No magnetic ordering was observed. It was found that at low temperatures, ρ varied as T2 and C∝T, indicating Fermi-liquid regime in Yb3Ga7Ge3 at low temperatures.
Density-functional-theory (DFT) computations on a Prussian blue analogue (PBA), nickel hexacyanof... more Density-functional-theory (DFT) computations on a Prussian blue analogue (PBA), nickel hexacyanoferrate, Ni2+ 3[Fe3+(CN)6]2·nH2O, predict the existence of a tetragonal (P 4 m2) crystal structure that is energetically degenerate with the previously reported cubic (F 43m) structure for this PBA. The proposed tetragonal structure satisfies observations, such as X-ray diffraction and magnetic measurements, that have been reported previously. A van der Waals corrected exchange-correlation functional is used in the DFT+U computations for an improved description of hydrogen bonding. The results provide strong support for a revised and simplified crystallographic description of Ni2+ 3[Fe3+(CN)6]2·nH2O, and show how H2O molecules stabilize the crystal structure and affect its magnetic and electronic properties. The symmetry lowering in nickel hexacyanoferrate is attributed to the hydration shell of the interstitial nickel cation. Calculations strongly suggest a maximum of n = 7 interstitial ...
Some recent papers [2],[3] report that the nonlinear susceptibility does not depend on quantum si... more Some recent papers [2],[3] report that the nonlinear susceptibility does not depend on quantum size effects. We show that this is not valid when considering the enchancement factor of one particle. Quantum size effects in nanoparticles not only exist but they have dominant contriubution. Our results in good agreement with the model proposed by Rautian [1].
We report the single crystal neutron diffraction studies done to resolve the room-temperature str... more We report the single crystal neutron diffraction studies done to resolve the room-temperature structure of Uranium antimonide, UNi0.5Sb2. The time-of-flight single-crystal neutron diffraction experiments at room temperature were done on the Single Crystal Diffractometer, SCD, at Los Alamos Neutron Science Center. Previous X-ray single crystal and neutron powder diffraction studies could not unambiguously resolve the structure because of the presence
We report on the dependence of the interatomic distances in the intermetallic compound UPdSn as d... more We report on the dependence of the interatomic distances in the intermetallic compound UPdSn as determined from the neutron diffraction data done on HIPD at Los Alamos spallation neutron source. The U-U distance gives a measure of the direct 5f-5f overlap. The U-Pd and U-Sn distances give a measure of 5f-ligand hybridization. Using the Rietveld refinement method, we were able
The UCu4+xAl8-x family crystallizes in the tetragonal ThMn12 - type structure in the range from 0... more The UCu4+xAl8-x family crystallizes in the tetragonal ThMn12 - type structure in the range from 0.1<= x<= 1.95. It has been reported that the Cu-poor compounds show antiferromagnetic long-range order, followed by a transition at x=1.15 to a heavy fermion behavior. We report on the results of thermal conductivity and the Seebeck coefficient as a function of temperature (1.8-300K). Thermal
UPdSn orders antiferromagnetically below 40K and undergoes a second antiferromagnetic transition ... more UPdSn orders antiferromagnetically below 40K and undergoes a second antiferromagnetic transition at about 27 K which has been attributed to spin reorientation. The magnetic properties of UPdSn are highly anisotropic with the c-axis as the hard magnetization direction. For magnetic fields applied in the basal plane, previous studies have observed significant domain repopulation effects as well as a spin-flop transition
We have performed RF skin depth measurements of selected uranium compounds in applied magnetic fi... more We have performed RF skin depth measurements of selected uranium compounds in applied magnetic fields up to 50 T. This technique is relatively new, as applied to metallic samples but is a useful probe of magnetotransport since the skin depth can be simply related to the magnetoresistance.
Examples of UNiAlD2.1 and UCoGe illustrate that the soft crystallographic direction coincides qui... more Examples of UNiAlD2.1 and UCoGe illustrate that the soft crystallographic direction coincides quite generally with the shortest U-U links in U intermetallics. It leads to a simple rule, that the easy magnetization direction and the soft crystallographic direction (in the sense of highest compressibility under hydrostatic pressure) must be mutually orthogonal.
The magnetic structure of two natural samples of goethite (α-FeOOH) with varying crystallinity wa... more The magnetic structure of two natural samples of goethite (α-FeOOH) with varying crystallinity was analyzed at 15 and 300 K by neutron diffraction. The well crystallized sample has thePb′nmcolor space group and remained antiferromagnetic up to 300 K, with spins aligned parallel to thecaxis. The purely magnetic 100 peak, identifying this color space group, was clearly resolved. The nanocrystalline sample shows a phase transition to the paramagnetic state at a temperature below 300 K. This lowering of the Néel temperature may be explained by the interaction of magnetic clusters within particles. The nuclear structure, refined with the Rietveld and pair distribution function methods, is consistent with reports in the literature.
... 10:30 AM–11:54 AM, Saturday, October 18, 2008. Union East, 3rd Floor Room: Wiggins Chair: Mig... more ... 10:30 AM–11:54 AM, Saturday, October 18, 2008. Union East, 3rd Floor Room: Wiggins Chair: Miguel Castro-Colin, The University of Texas at El Paso Abstract ID: BAPS.2008.TS4CF.H6.2. Abstract: H6.00002 : Evolution of Magnetism in Sr$_{2-x}$La$_{x}$FeO$_{4 }$ system of ...
The UTX intermetallic compounds, where T is the transition metal and X is p-electron element, wer... more The UTX intermetallic compounds, where T is the transition metal and X is p-electron element, were found to crystallize mainly in two large groups, the orthorhombic CeCu2 type of structure and the hexagonal ZrAlNi type of structure. In both groups of compounds, bulk and neutron-diffraction measurements have revealed a large variety of magnetic ordering phenomena depending on the degree of the 5f-ligand hybridization. The 5f-ligand hybridization is very sensitive to the overlap of the respective wavefunctions, which can be effectively controlled by external pressure. Applied pressure can be expected to increase the 5f-ligand hybridization. We have summarized existing and new pressure studies of the ordering temperatures and the critical fields of various antiferromagnetic UTX compounds (T = Ni, Co, Ir; X = Al, Ga, Ge) by means of magnetoresistance studies in magnetic fields up to 18 T. The studies were performed on single crystals under hydrostatic pressure up to 10 kbar. The observe...
ABSTRACT Yb3Ga7Ge3 and YbGa4Ge2 were obtained from reactions of Yb and Ge in excess liquid galliu... more ABSTRACT Yb3Ga7Ge3 and YbGa4Ge2 were obtained from reactions of Yb and Ge in excess liquid gallium. The crystal structure of Yb3Ga7Ge3 was refined using X-ray and neutron diffraction data on selected single crystals. Yb3Ga7Ge3 crystallizes in the monoclinic space group C2/c with lattice constants a=12.2261(20) Å, b=10.7447(20) Å, c=8.4754(17) Å and β=110.288(30)° (neutron diffraction data). The crystal structure of Yb3Ga7Ge3 is an intergrowth of planar layers of YbGaxGey and puckered layers of (Ge)n. YbGa4Ge2 crystallizes in a modified PuGa6 structure type in the tetragonal polar space group I4cm with lattice constants a=b=5.9874(6) Å and c=15.1178(19) Å. The structure of YbGa4Ge2 is an intergrowth of puckered Ga layers and puckered GaxGey layers with Yb atoms residing within the channels formed by the connection of the two layers. Physical properties, resistivity (ρ), magnetic susceptibility (χ) and specific heat (C) were measured for Yb3Ga7Ge3. No magnetic ordering was observed. It was found that at low temperatures, ρ varied as T2 and C∝T, indicating Fermi-liquid regime in Yb3Ga7Ge3 at low temperatures.
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