Small Effective Magnetic Moment Research Articles

Itinerant antiferromagnetism in Co3S4−δ

We present experimental and theoretical investigations for the cobalt thiospinel ${\mathrm{Co}}_{3}{\mathrm{S}}_{4\ensuremath{-}\ensuremath{\delta}}$. High-quality samples of ${\mathrm{Co}}_{3}{\mathrm{S}}_{4\ensuremath{-}\ensuremath{\delta}}$ $(\ensuremath{\delta}\ensuremath{\sim}0.1)$ were prepared so as to measure their intrinsic properties. The measurements of magnetic susceptibility, specific heat, and electrical transport consistently indicate an antiferromagnetic transition at $\ensuremath{\sim}60$ K, which is attributed to long-range magnetic ordering in the $\mathrm{Co}(A)$ ($A$-site Co ions) diamond sublattice. In addition, there exists a short-range magnetic ordering at around 120 K associated with the magnetic frustrations. The high-temperature magnetic susceptibility obeys Curie-Weiss law, from which a small effective magnetic moment of $1.0\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ per formula unit is yielded. The main experimental results can be interpreted by the density-functional-theory calculations with a Hubbard $U$ correction of $\ensuremath{\sim}0.5$ eV. Combining the experimental measurements with the theoretical calculations, we conclude that ${\mathrm{Co}}_{3}{\mathrm{S}}_{4}$ represents a rare example of itinerant-electron diamond-lattice antiferromagnet with moderate electron correlations.

Layered quaternary chalcogenides KMgCuSe2 and KMgCuTe2 with paramagnetic semiconducting behavior

Here we report the synthesis of two new quaternary chalcogenides KMgCuSe2 and KMgCuTe2. Both single-crystal and polycrystalline samples have been obtained using self-flux method and high temperature reaction. These two compounds adopt ThCr2Si2-type structure which is composed of edge-sharing [Mg0.5Cu0.5Se4] and [Mg0.5Cu0.5Te4] tetrahedral layers separated by K+ ions. Single-crystal refinement reveals the random distribution of Mg and Cu with ratio of 1:1 in the centre of tetrahedron motifs. The Mg-Se and Mg-Te bond lengths in KMgCuSe2 and KMgCuTe2 are markedly shorter than those in binary MgSe and MgTe, but are comparable with the Cu-Se and Cu-Te bond lengths in binary Cu chalcogenides. In addition, the tetrahedral configurations in KMgCuSe2 and KMgCuTe2 are highly distorted with strong compression along c axis. These two new Mg chalcogenides are semiconductors with the indirect band gaps estimated from optical absorption spectra as 1.26 and 1.36 eV for KMgCuSe2 and KMgCuTe2. Magnetic susceptibility measurements indicates the paramagnetic behavior of KMgCuSe2 and KMgCuTe2 with small effective magnetic moment ueff (0.35 and 0.31 μB per Mg/Cu).

Widely spaced planes of magnetic dimers in theBa6Y2Rh2Ti2O17−δhexagonal perovskite

We report the synthesis and initial characterization of Ba6Y2Rh2Ti2O17-{\delta}, a previously unreported material with a hexagonal symmetry structure. Face-sharing RhO6 octahedra form triangular planes of Rh2O9 dimers that are widely separated in the perpendicular direction. The material displays a small effective magnetic moment, due to the Rh ions present, and a negative Curie-Weiss temperature. The charge transport and optical band gaps are very similar, near 0.16 eV. A large upturn in the heat capacity at temperatures below 1 K, suppressed by applied magnetic fields larger than {{\mu}0H = 2 Tesla, is observed. A large T-linear term in the specific heat ({\gamma}=166 mJ/mol f.u-K2) is seen, although the material is insulating at low temperatures. These results suggest the possibility of a spin liquid ground state in this material.

Vacancy ordering in Pd11Bi2Se2 - Crystal structure and properties

The crystal structure of Pd11Bi2Se2 was determined and refined from X-ray single crystal data (space group Fd3¯m, a = 12.4879(14) Å, Z = 8). In contrast to the earlier reported Pd3(Bi0.6Se0.4), the title compound crystallizes in a 2 × 2 × 2 superstructure of the BiF3 type with ordered bismuth and selenium distribution and an ordered vacancy according to Pd11□Bi2Se2. The vacancy is located at the center of a palladium tetrahedron capped with a bismuth tetrahedron (stella quadrangula). Pd11Bi2Se2 is isopointal to Li13In3 but shows different ordering of the minority components. Pd11Bi2Se2 is inert to water, organic solvents and concentrated hydrochloric acid and its melting point is 905(1) K. It exhibits a very small effective magnetic moment of μeff = 0.0114(2) μB per palladium atom. Pd11Bi2Se2 does not take up hydrogen up to 7.2(2) MPa hydrogen pressure and temperatures up to 703 K. In the electronic structure, the region near the Fermi level is dominated by almost filled Pd 4d-states. Low yet non-zero density of states and a pseudo-gap at the Fermi level might indicate Pd11Bi2Se2 to be a poor metal.

Stoner-enhanced paramagnetism in tungsten tetraboride

We demonstrate that tungsten tetraboride (WB4), a heavy transition metallic compound without magnetic atoms, is an exchange-enhanced paramagnet revealed by the magnetization and specific heat measurements. WB4 has a small effective magnetic moment of 0.53 μB/fu. The high magnetic susceptibility in the magnitude of 1 memu (mol·Oe)−1 below 10 K obeys quadratic temperature dependence. The upturn behavior of CP/T versus T2 at low temperatures is attributed to the electron-paramagnon interactions. A high Stoner enhancement parameter, Z = 0.93, was derived to explain the enhanced paramagnetism based on the Stoner model.

Oxidation State of Uranium in A6Cu12U2S15(A = K, Rb, Cs) Compounds

Black single crystals of A(6)Cu(12)U(2)S(15) (A = K, Rb, Cs) have been synthesized by the reactive flux method. These isostructural compounds crystallize in the cubic space group Ia ̅3d at room temperature. The structure comprises a three-dimensional framework built from US(6) octahedra and CuS(3) trigonal planar units with A cations residing in the cavities. There are no S-S bonds in the structure. To elucidate the oxidation state of U in these compounds, various physical property measurements and characterization methods were carried out. Temperature-dependent electrical resistivity measurement on a single crystal of K(6)Cu(12)U(2)S(15) showed it to be a semiconductor. These three A(6)Cu(12)U(2)S(15) (A = K, Rb, Cs) compounds all exhibit small effective magnetic moments, < 0.58 μ(B)/U and band gaps of about 0.55(2) eV in their optical absorption spectra. From X-ray absorption near edge spectroscopy (XANES), the absorption edge of A(6)Cu(12)U(2)S(15) is very close to that of UO(3). Electronic band structure calculations at the density functional theory (DFT) level indicate a strong degree of covalency between U and S atoms, but theory was not conclusive about the formal oxidation state of U. All experimental data suggest that the A(6)Cu(12)U(2)S(15) family is best described as an intermediate U(5+)/U(6+) sulfide system of (A(+))(6)(Cu(+))(12)(U(5+))(2)(S(2-))(13)(S(-))(2) and (A(+))(6)(Cu(+))(12)(U(6+))(2)(S(2-))(15).

Synthesis, micro-structural and magnetic properties of Mn-doped ZnO nanowires

Single-crystalline Mn-doped ZnO nanowires of different compositions were synthesized by chemical vapor deposition. Their micro-structures were characterized by high-resolution transmission electron microscopy and X-ray diffraction. The results reveal that Mn doping leads to production of planar and point defects, lattice expansion and disorder. These micro-structural features are also reflected by characteristic changes in the Raman spectra of the nanowires, such as the red-shift and asymmetric broadening of the E2H mode, the appearance of an additional mode, and the anomalous enhancement of the E1(LO) mode. All the doped nanowires show ferromagnetism with a Curie temperature above 350 K. The small effective magnetic moment of ∼0.02 μB/Mn suggests the presence of isolated Mn ions and/or antiferromagnetic superexchange interactions. The long-range ferromagnetic interaction is understood in terms of two possible mechanisms, including the percolation of bound magnetic polarons and surface-hole-mediated ferromagnetic coupling.

Low-moment antiferromagnetic ordering in triply charged cubic fullerides close to the metal-insulator transition

We report on the ambient pressure $^{13}\text{C}$ and $^{133}\text{C}\text{s}$ NMR study of disorder-free A15-structured ${\text{Cs}}_{3}{\text{C}}_{60}$, which shows non-BCS superconductivity at 38 K under pressure. Temperature-independent $^{13}\text{C}$ and $^{133}\text{C}\text{s}$ spin-lattice relaxation rates prove an insulating ground state with a small effective magnetic moment $1.3--1.6{\ensuremath{\mu}}_{B}$ for $Tg100\text{ }\text{K}$. Below 46 K, A15 ${\text{Cs}}_{3}{\text{C}}_{60}$ orders into an antiferromagnetic structure best described by a magnetic wave vector, $\mathbf{q}=(\frac{1}{2},\frac{1}{2},\frac{1}{2})$ with a staggered magnetic moment $\ensuremath{\sim}0.9{\ensuremath{\mu}}_{B}$ per ${\text{C}}_{60}$. The large $(U/W)$ ratio $(\ensuremath{\sim}2.2)$, the opening of a gap in the electronic excitation spectrum and the small ${\text{C}}_{60}^{3\ensuremath{-}}$ magnetic moment all underline the importance of electronic correlations in A15 ${\text{Cs}}_{3}{\text{C}}_{60}$.

Preparation and Properties of Novel Intergrowth System of BiS(VS2)n (1.LEQ.n.LEQ.15)

Ternary sulfides of BiS(VS2)n (1 ≤ n ≤ 15) were prepared by heating the elemental mixtures in evacuated silica tubes at 1073 K. X-ray diffraction and electron diffraction measurements showed that BiS(VS2)1.50 has a misfit layer structure, where the BiS layers are randomly lacked from the known misfit layer sulfide of (BiS)1.16VS2. BiS(VS2)1.50 has a good conduction, showing a phase transition around 150 K possibly due to the CDW instability. The conduction of BiS(VS2)1.50 was interpreted by the electron donation from BiS into the semiconductive VS2. BiS(VS2)1.50 showed an antiferromagnetic ordering at ca. 30 K, and has a fairly small effective magnetic moments suggesting the strong itinerancy. It was found that the compounds of BiS(VS2)n with 3 ≤ n ≤ 15 have the intergrowth structures composed of BiS(VS2)3 and VS2 phases. Such a great variety of composite materials have never been investigated so far.

The Magnetic Susceptibilities and Electron Paramagnetic Resonance Spectra of 6H-Perovskites Ba3PrM2O9 (M = Ir, Ru)

Abstract The magnetic properties of quaternary oxides Ba3PrM2O9 and Ba3CeM2O9 (M = Ir, Ru) have been investigated. They crystallize in the 6H-perovskite structure with the space group P63/mmc, in which the cation sites with the face-sharing octahedra are occupied by Ir (or Ru) ions, and those within the corner-sharing octahedra are occupied by Pr (or Ce) ions. Magnetic susceptibility measurements for Ba3PrIr2O9 show that an antiferromagnetic interaction between two Ir ions in the Ir2O9 dimer results in a large temperature-independent paramagnetic susceptibility over a wide temperature range. Another interesting result is in the small effective magnetic moments for Ba3PrIr2O9 (0.31(1) μB) and for Ba3PrRu2O9 (0.75(1) μB). The electron paramagnetic resonance (EPR) spectrum of Pr4+ in these compounds was measured by diluting them in the corresponding isomorphous compounds Ba3CeIr2O9 and Ba3CeRu2O9 and lowering the temperature to 4.2 K. A very large hyperfine interaction with the 141Pr nucleus was observed. The results were analyzed based on the weak field approximation. The measured g values are much smaller than |−10/7|, showing that the crystal field effect on the behavior of a 4f electron is large. The low g values correspond to the small effective magnetic moments of the Pr compounds.

Magnetic properties of RRhO 3 (R=rare earth)

RRhO 3 (R=rare earth except Ce and Pm) was prepared by a solid-state reaction, and its crystallographic, magnetic, and electric properties were investigated. RRhO 3 has an orthorhombic perovskite-type structure of the space group Pbnm. RRhO 3 shows Curie–Weiss paramagnetism above 5 K. On the other hand, EuRhO 3 shows antiferromagnetic behavior. The Rh 3+ ion, which seems to be in the low-spin state, has a very small effective magnetic moment ( P eff=0.295 μ B/ion). The P eff value of the RRhO 3 compounds shows the same dependence on the number of 4 f electrons as the gJ value of the rare-earth ions. The rare-earth ions make a major contribution to the magnetic moment of RRhO 3. The resistivity of all RRhO 3 shows an activation-type (or semiconductor-like) temperature dependence.

Characterization of Ternary Compounds in the BaO:Fe2O3:TiO2System: Ba6Fe45Ti17O106and BaFe11Ti3O23

Single crystals of Ba6Fe45Ti17O106and BaFe11Ti3O23were obtained as major and minor coproducts, respectively, by slow-cooling an off-stoichiometric BaO:Fe2O3:TiO2melt. The former compound exhibits variable stoichiometry, Ba6Fe48−xTi14−xO106, with the Fe:Ti ratio dependent upon the partial pressure of oxygen. The value ofxcorresponds to the equivalents of reduction that occur to maintain electroneutrality as the Ti-content increases. When prepared in air, this phase occurs atx=3 with the stoichiometry Ba6Fe45Ti17O106, while in 100% oxygen thex-value approaches zero with the resulting stoichiometry Ba6Fe48Ti14O106(all Fe3+and Ti4+). The structures of Ba6Fe45Ti17O106and BaFe11Ti3O23were solved using single-crystal X-ray diffraction methods. Ba6Fe45Ti17O106was prepared in polycrystalline form, and further structural details, including accurate Fe/Ti occupancy factors, were determined by a combined refinement using neutron and synchrotron powder diffraction data. (Ba6Fe45Ti17O106: Space groupC2/m(No. 12);a=19.390(1) Å,b=20.260(1) Å,c=10.076(1) Å,β=105.27(1)°;V=3818.5(3)Å3;Z=2;ρcalc=5.08 g/cm3. Ba6Fe11Ti3O23= Space groupC2/c (No. 15);a=19.561(1) Å,b=8.6614(7) Å,c=10.120(1) Å,β=105.62(1)°;V=1651.1(3) Å3;Z=4;ρcalc=5.08 g/cm3.) Both compounds adopt eight-layer close-packed structures built from alternatingccpandhcp[O, (Ba, O)] layers stacked along thea-direction with a (ch)4repeat sequence. Both structures feature octahedral sites occupied by a mixture of Fe and Ti as well as tetrahedral sites occupied by Fe3+the structural formulas areXIIBa6IVFe6VI(Fe39Ti17)O106andXIIBaIVFe2VI(Fe9Ti3)O23. Both compounds are partially reduced; the former contains 3 moles of Fe2+(or Ti3+) per formula unit, and the latter contains 1mole. The formation of Fe2+is considered more likely than Ti3+, but could not be experimentally confirmed. BaFe11Ti3O23is apparently metastable in air when cooled from above the solidus and could not be prepared as a polycrystalline sample. Indexed experimental X-ray powder diffraction data for Ba6Fe45Ti17O106are given. Polycrystalline samples of this compound were used to measure its magnetic and electrical properties. The magnetic behavior of Ba6Fe45Ti17O106above room temperature up to 1073 K was found to obey the Curie–Weiss law, which indicated a small effective magnetic moment (34μBper mole Ba6Fe45Ti17O106) and a large negative temperature intercept (−806 K). Electrical resistivity measurements between room temperature and 120 K revealed nonmetallic behavior with an activation energy on the order of 0.17eV. At 347 MHz under ambient conditions, Ba6Fe45Ti17O106exhibited a relative permittivity of 24 and a dielectric loss tangent of 0.10.

Magnetic properties of tetravalent praseodymium perovskites BaPrO 3, BaCe yPr 1− yO 3, and Sr yBa 1− yPrO 3

Tetravalent praseodymium perovskites BaPrO 3, BaCe y Pr 1− y O 3, and Sr y Ba 1− y PrO 3 were prepared, and their magnetic susceptibilities were measured in the temperature range between 4.2 and 300 K. Magnetic ordering found in the BaPrO 3 (the transition temperature is 11.6 K) is weakened with substitution of Sr for Ba and much more weakened with substitution of Ce for Pr. Above this transition temperature, the susceptibility decreases anomalously with increasing temperature. A magnetic hysteresis was found at 4.5 K for all the compounds studied here. The magnetic susceptibility above the transition temperature is composed of a Curie—Weiss term associated with a small effective magnetic moment of Pr 4+ and a large temperature-independent paramagnetism. The effective magnetic moment of the Pr 4+ ion in Sr y Ba 1− y PrO 3 increases with strontium concentration ( y). This result is in accordance with the result obtained from the electron paramagnetic resonance spectrum of Pr 4+ doped in Sr y Ba 1− y CeO 3.

Magnetic, thermal, transport, and structural properties of Sr2RuO4+ delta : Enhanced charge-carrier mass in a nearly metallic oxide.

Measurements of electrical resistivity, magnetic susceptibility, heat capacity, and powder neutron diffraction are presented on ${\mathrm{Sr}}_{2}$${\mathrm{RuO}}_{4+\mathrm{\ensuremath{\delta}}}$. Specimens with low-impurity levels allow magnetic susceptibility in the range 5T350 K to be measured; these measurements indicate a small effective magnetic moment of ${\mathrm{\ensuremath{\mu}}}_{\mathrm{eff}}$\ensuremath{\approxeq}1${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ per Ru ion. Electrical resistivity displays nonmetallic behavior in the range 1.2T300 K with \ensuremath{\rho}(295 K)=51 m\ensuremath{\Omega} cm. A rather large linear heat-capacity coefficient of \ensuremath{\gamma}=45.6 mJ/mol ${\mathrm{K}}^{2}$ is reported; speculation is made regarding its origin. Rietveld refinement of powder-neutron-diffraction data provide insight into the physical properties and reveal interesting differences to isostructural ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$. Comparisons are drawn to other transition-metal oxides.

Magnetic behaviour and hyperfine interactions in AlFeCe metallic glasses

57Fe Mössbauer effect and magnetic susceptibility measurements have been performed on the new glassy alloys Al 90Fe 5Ce 5, Al 87Fe 6.7C 6.3, Al 87Fe 8.7Ce 4.3, and Al 87Fe 9.3Ce 3.7. It is found that Fe atoms are not magnetically ordered in the Fe-rich glasses down to 4.2 K. The disorder inherent to glasses is manifested in the distribution of the electric quadrupole splittings, which is shown to be well described by a Gaussian shape. The magnetic susceptibility of the alloys follows the Curie-Weiss law between 4.2 K and room temperature. The small effective magnetic moment values suggest mixed-valence behaviour.

Light-induced oxidation of iron atoms in a photosensitive nitrile hydratase

The photoactivation process of a photosensitive nitrile hydratase (NHase) from Rhodococcus sp. N-771 has been investigated by 57Fe Mössbauer spectroscopy and magnetic susceptibility measurements in order to clarify the behavior of iron atoms in the enzyme. Mössbauer spectra of inactive NHase gave two symmetric-doublet components indicating the presence of two iron species, while that of the active NHase gave a single symmetric doublet indicating the presence of a single iron species. Magnetic susceptibility measurements of the inactive and active HNase both showed small effective magnetic moments. These results led us to conclude that one of the two iron atoms incorporated in the NHase is oxidized during photoactivation, namely from a low spin ferrous to a low spin ferric state. This is the first observation of an intramolecular photooxidation phenomena involving iron in a single protein molecule.

The magnetic moment of Se2

Atoms of the oxygen group form diatomic molecules with a multiplet ground state. Of these, O2 and S2 conform to Hund’s (b) coupling and have an appreciable magnetic moment, whereas Te2 is better described as having case (c) coupling with a very small effective magnetic moment. Although the Se2 molecule is intermediate between these two cases, it is closer to case (c) than to case (b). A method of calculating the magnetic moment and Zeeman effect of a molecule of this series with Hund’s case (c) coupling is described and applied to Se2. The calculations result in a value of 5.97×10−2 μB for the mean effective moment of the Se2 molecule at 1000 K in a field of 14 kG. This value was found to be consistent with the results obtained experimentally by the use of a molecular beam deflection technique similar to that of Stern and Gerlach.