Static Magnetic Susceptibility Research Articles

Neutron studies of cation disorder in Zn 2FeV 3O 11− δ

Polycrystalline Zn 2FeV 3O 11− δ samples were studied by neutron diffraction and ac magnetic susceptibility in the temperature range of 10–300 K. This material, crystallizing in the triclinic space group P1, has a complicated structure with cation disorder. Down to 10 K, no magnetic long-range order was found, in contrast to suggestions based on the temperature dependence of the static magnetic susceptibility and electron paramagnetic resonance (EPR). Essential differences in the positions of the metal ions were observed relative to those calculated earlier from X-ray diffraction (XRD). It is proposed that disorder of iron and zinc atoms could be responsible for significant differences in the physical properties reported for this compound.

Antiferromagnetic spin wave inCe2PdGe6

The ternary compound ${\mathrm{Ce}}_{2}{\mathrm{PdGe}}_{6}$ exhibits antiferromagnetic ordering below the temperature $11.4\ifmmode\pm\else\textpm\fi{}0.2\mathrm{K},$ as revealed in the electrical-resistivity, static magnetic susceptibility, and low-temperature specific-heat data. The entropy associated with the magnetic structure of ${\mathrm{Ce}}_{2}{\mathrm{PdGe}}_{6}$ was found to be close to the theoretical value of $2R\mathrm{ln}2,$ which would be expected for a doublet ground state of ${\mathrm{Ce}}^{+3}$ ions in the compound ${\mathrm{Ce}}_{2}{\mathrm{PdGe}}_{6}.$ The magnetic contribution to the heat capacity of ${\mathrm{Ce}}_{2}{\mathrm{PdGe}}_{6}$ below N\'eel temperature ${T}_{N}$ was found to depend on the cube of temperature, which furnishes perhaps the most direct experimental testimony of the whole spin-wave theory for an antiferromagnetic material.

A Series of Transition Metal Bis(dicyanobenzenedithiolate) Complexes [M(dcbdt)2] (M = Fe, Co, Ni, Pd, Pt, Cu, Au and Zn)

AbstractA series of new M[(dcbdt)2]−z complexes of the dicyanobenzodithiolate (dcbdt) ligand with a range of transition metals (M = Co, Pd, Pt, Cu, Au and Zn) in different oxidation states (z = 0.4, 1, 2) were prepared as their nBu4N salts and characterised by X‐ray diffraction, cyclic voltammetry, EPR and static magnetic susceptibility. Their properties are discussed in comparison with the Ni and Fe analogues described by us recently. The structures of these complexes belong to four distinct groups: i) the ZnII compound 10 is triclinic P$\bar 1$ with the metal in a tetrahedral coordination geometry; ii) other MII complexes [M = Pt (8), Pd (7), Co (3) and Cu (5)] are monoclinic C2/m, and are isostructural with the NiII analogue, presenting a perfectly planar square geometry; iii) the CoIII compound 4 is triclinic P$\bar 1$ , and isostructural with the Fe and Ni analogues, with a strong dimerisation of the M(dcbdt)2 units and the metal in a square‐pyramidal coordination geometry; iv) the MIII salts with M = Au (2), Cu (6) and Pt (9) are monoclinic P21/c and the complexes are arranged as pseudo‐dimers. The EPR and static magnetic‐susceptibility measurements show that the CoII (3), CuII (5), PtIII (9) and CoIII (4) complexes are paramagnetic corresponding to an S = 1/2 state, except for CoIII, which is in a high‐spin S = 1 configuration. The solid state EPR spectra of the CoII compound presents a hyperfine structure typical of the I = 7/2 59Co. The temperature dependence of the paramagnetic susceptibility of the PtIII compound follows a singlet‐triplet model with a dimer antiferromagnetic coupling, J, of 984 K. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The permittivity of a monatomic gas with spatial dispersion

The longitudinal, el(ω, k), and transverse, etr(ω, k), permittivities of a monatomic gas were calculated. The frequency ranges in which the permittivity e(ω) and permeability μ(ω) of a gas without spatial dispersion have a physical meaning were determined. The limiting magnetic susceptibility χ(ω) at ω=0 and the static magnetic susceptibility were found. The question of whether an electromagnetic wave with antiparallel group and phase velocities can propagate through a monatomic gas is discussed.

The magnetization behavior of lightly doped YBa2Cu3O6+

Abstract The static magnetic susceptibility of two different YBa 2 Cu 3 O 6.30 samples shows a peak near to 45 K; the peak shows a dependence on the field and on the magnetic history. This feature has been explained by the combined effect of regions with a Curie-like behavior and superconducting regions. The origin of these regions in the material has been discussed.

Magnetic Properties of a New One-Dimensional Vanadium Oxide with the Hollandite Structure.

ABSTRACTThe magnetic properties of the first hollandite-type vanadium oxide containing anions in the 2×2 channels, V7.22O8(OH)8(Cl)0.77(H3O)2.34, are studied using static (DC) and dynamic (AC) magnetic susceptibilities. From the high-temperature Curie-Weiss behavior the effective magnetic moment is found consistent with the 3+ vanadium oxidation state; the negative Curie-Weiss temperature Θ ≈ -500 K indicates strong antiferromagnetic exchange. The DC magnetic susceptibility shows a rapid increase and the AC susceptibility shows a maximum at about 20 K, indicating magnetic phase transition. The field-cooled and zero-field-cooled susceptibilities diverge below the transition temperature. The real and imaginary components of the AC susceptibility show frequency dependence and shift of maximum toward lower temperatures with decreasing frequency. Analysis of the frequency dependences reveals at least three different relaxation processes existing around and below the transition temperature. The temperature dependences of their relaxation times were obtained using Cole-Cole analysis. We show that the magnetic behavior observed is well explained by the random-field Ising model, with randomness brought on by vacancies in vanadium sites.

Contribution of Degenerate Molecular Orbitals to Molecular Orbital Angular Momentum in Molecular Magnet Fe(Pc)(CN)2

We measured the static magnetic susceptibility and the electron spin resonance of the Fe(Pc)(CN) 2 complexes, and investigated the molecular magnetism of the unit Fe(Pc)(CN) 2 . The magnetic susceptibility shows a highly anisotropic Curie behavior. Based on the electron spin resonance, we found a highly anisotropic g -value ( g 1 = 3.62, g 2 = 1.11, and g 3 = 0.52) in the molecular unit Fe(Pc)(CN) 2 . This anisotropy is caused by the molecular orbital angular momentum in the degenerate next highest occupied molecular orbitals of the molecular unit Fe(Pc)(CN) 2 . Since the molecular unit Fe(Pc)(CN) 2 has a unique structure with fourfold symmetry, the molecular orbital angular momentum has a finite value of l z ∼+1 and -1. The anisotropic molecular magnetism of the unit Fe(Pc)(CN) 2 contributes the highly anisotropic Curie behavior. The molecular unit Fe(Pc)(CN) 2 is a good candidate for a molecular magnet having high magnetic anisotropy.

Expanded Bethe–Peierls approximation for the Ising model with S = 1/2 and 1

AbstractA expanded Bethe–Peierls approximation has been used to study the Ising model on honeycomb lattice, square lattice, kagomé lattice, triangular lattice and simple cubic lattice with spin S = 1/2 and 1. The spatial dimensionality of system is distinguished for different lattices. It is found that the transition temperatures on different lattices are much closer to the real values than those obtained by the effective field theory and the Bethe lattice approximation, and the transition temperatures of systems on kagomé lattice (z = 4) and trianguilar lattice (z = 6) are lower than those on square lattice (z = 4) and simple cubic lattice (z = 6), respectively. The static magnetic susceptibilities are also calculated. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of a Peaked Feature in the Magnetic Susceptibility of YBa2Cu3O6.30 Samples

The static magnetic susceptibility of two different YBa2Cu3O6.30 samples has been measured at different fields in the range 2 - 300 K, using a superconducting quantum interference device magnetometer; one sample has been prepared by oxygen intercalation, the other one by deintercalation. The susceptibility shows a peak near 45 K in both samples, which depends on the field and the magnetic history. The susceptibility of semiconducting and superconducting compounds, with an oxygen content O6.20 and O6.41, respectively, has also been investigated. The presence of the peak in the YBa2Cu3O6.30 samples has been explained by the combined effect of regions with a Curie-like behaviour and superconducting regions. The origin of these regions is discussed.

The isotropic and anisotropic interactions of the alternating ferromagneticquasi-one-dimensional magnet [Cu4(ndpa)2(H2O)6Cl2]·4H2O

The magnetic properties of [Cu4(ndpa)2(H2O)6Cl2]·2H2Oare studied by static and dynamic magnetic susceptibility measurements.The static susceptibility measurements between 2 and 300 K revealferromagnetically coupled Cu(II) dimers (J/kB = +24.0 ± 0.5 K).Two further exchange constants J′/kB = −0.40 ± 0.02 Kand J′′/kB = 2.2 ± 0.2 Kare determined by zero-field ac-susceptibility measurements in the temperaturerange between 12 and 0.4 K. The exchange couplings are assigned bymeans of electron spin resonance measurements which show that Cu4: Clrealizes a ferromagnetic alternating spin-1/2Heisenberg chain with an antiferromagnetic interchain coupling.

Magnetic Properties and Spin Kinetics of Two-Dimensional Heisenberg Antiferromagnets

In this report we present our study of two-dimensional Heisenberg magnets based on the picture of thermally excited skyrmions. The local order parameter, energy spectrum of elementary spin excitations above the skyrmion background, the skyrmion averaged radius and static magnetic susceptibility were obtained by the Green functions method. There was calculated the rate of nuclear relaxation caused by the interaction of nuclear spins with above mentioned spin excitations. The contribution of Moriya–Dsyloshinskii and anisotropic symmetric interactions into EPR line was considered. A comparison with NMR and neutron scattering experiments in cuprates and with the results obtained by other methods is given. We discuss the consequences of an interaction between skyrmions as the result of the spin fluctuations.

Anomalous properties of a large magnetic moment in a fourfold potential

An experimental study of magnetic moments placed in a fourfold potentialis presented here. The system used is a monocrystal of LiY0.99Dy0.01F4,where the only magnetic ions are the Dy3+ions. From static magnetic susceptibility measurements, it is shown that the Dy3+ion has an easy magnetization plane, with an additional anisotropy in theeasy plane. Low frequency electron paramagnetic resonance experimentsare presented here and up to nine resonance lines have been found.Some of them are in agreement with known properties of the Dy3+ ion in LiY0.99Dy0.01F4,but others cannot be explained within the framework of the commonlyused effective Hamiltonian. The behaviour of these new lines isconsistent with a magnetic tunnelling effect. Finally, spin echoes havebeen observed, allowing the determination of the relaxation timeT2and the coupling coefficient for several orientations of the magnetic field.

A New Packing Pattern of the Conducting BEDO-TTF Complexes

The crystal structure of (BEDO-TTF) 4 Pd(CN) 4 (H 2 O) x (x 1) showed the exceptional donor arrangement as a conductive BEDO-TTF complex. The crystal structure is understood as a modified I 3 -type, which is the most common packing pattern of the metallic complexes based on this donor molecule. Also, the title complex showed the abnormal EPR line width broadening on cooling despite of trivial metallic behaviors in the conductivity and static magnetic susceptibility.

Magnetic phase diagram and superconductivity in κ-type ET salts

We measured the static magnetic susceptibility of κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl. The temperature dependence of the susceptibility can be explained by an activating-type temperature dependence in the overall paramagnetic state below about 100 K. There is no anisotropic behavior in the paramagnetic state within the experimental resolution. Therefore, in contrast to the superconducting salt κ-(BEDT-TTF) 2 X (X=Cu(NCS) 2 , Cu[N(CN) 2 ]Br) the corresponding phase transition at T* (= 46-50 K in X = Cu(NCS) 2 , 37-38 K in X = Cu[N(CN) 2 ]Br) does not exist in the present compound.

Analytical results for the high-temperature expansion of the one-dimensionals=1XXZmodel

Recently Rojas et al. [J. Math. Phys. 43, 1390 (2002)] obtained a closed analytical expression for the coefficients of arbitrary order in the cumulant expansion of a one-dimensional periodic chain model with nearest-neighbor interaction and spatial translation invariance; that approach can be applied equally well to both nonintegrable and exact integrable models. Here, we obtain the exact analytic expressions for the six lowest-order terms of the high-temperature expansion of the Helmholtz free energy per site of the nonintegrable one-dimensional spin-$1$ $\mathrm{XXZ}$ Heisenberg model. Our analytical results for the specific heat and the static magnetic susceptibility are compared, up to order ${\ensuremath{\beta}}^{6}$ for the ferromagnetic and antiferromagnetic phases, with the respective numerical results of a periodic chain with ten sites $(N=10)$ and numerical results in the literature [Bl\"ote, Physica B 79, 427 (1975)]. A very good agreement is obtained for both phases in the high-temperature regime.

Synthesis, X‐ray Powder Structure, and Magnetic Properties of Layered NiII Methylphosphonate, [Ni(CH3PO3)(H2O)], and NiII Octadecylphosphonate, [Ni{CH3‐(CH2)17‐PO3}(H2O)

[Ni(CH(3)PO(3))(H(2)O)] (1) and [Ni(CH(3)-(CH(2))(17)-PO(3))(H(2)O)] (2) were synthesised by reaction of NiCl(2).6 H(2)O and the relevant phosphonic acid in water in presence of urea. The compounds were characterised by elemental and thermogravimetric analyses, UV-visible and IR spectroscopy, and their magnetic properties were studied by using a SQUID magnetometer. The crystal structure of 1 was determined "ab initio" from X-ray powder diffraction data and refined by the Rietveld method. The crystals of 1 are orthorhombic, space group Pmn2(1), with a=5.587(1), b=8.698(1), c=4.731(1) A. The compound has a hybrid, layered structure made up of alternating inorganic and organic layers along the b direction of the unit-cell. The inorganic layers consist of Ni(II) ions octahedrally coordinated by five phosphonate oxygen atoms and one oxygen atom from the water molecule. These layers are separated by bilayers of methyl groups and van der Waals contacts are established between them. A preliminary structure characterisation of compound 2 suggests the crystallisation in the orthorhombic system with the following unit-cell parameters: a=5.478(7), b=42.31(4), c=4.725(3) A. The oxidation state of the Ni ion in both compounds is +2, and the electronic configuration is d(8) (S=1), as determined from static magnetic susceptibility measurements above 50 K. Compound 1 obeys the Curie-Weiss law at temperatures above 50 K; the Curie (C) and Weiss (theta) constants were found to be 1.15 cm(3) K mol(-1) and -32 K, respectively. The negative value of theta indicates an antiferromagnetic exchange coupling between near-neighbouring Ni(II) ions. No sign of 3D antiferromagnetic long-range order is observed down to T=5 K, the lowest measured temperature. Compound 2 is paramagnetic above T=50 K, and the values of C and theta were found to be 1.25 cm(3) K mol(-1) and -24 K, respectively. Below 50 K the magnetic behavior of 2 is different from that of 1. Zero-field cooled (zfc) and field-cooled (fc) magnetisation plots do not overlap below T=21 K. The irreversible magnetisation, DeltaM(fc-zfc), obtained as a difference from fc and zfc plots starts to increase at T=20 K, on lowering the temperature, and it becomes steady at T=5 K. The presence of spontaneous magnetisation below T=20 K indicates a transition to a weak-ferromagnetic state for compound 2.

NMR probe of phase separation in lightly doped manganites

The 55Mn NMR spectra in an ordered state in a local field and the static magnetic susceptibility were measured for the polycrystalline (LaMn) 1–2 x O 3 ( x=0, 0.03) samples with different concentrations of vacancies in the cation sublattice. It is shown that microscopic regions with a different magnetic structure and manganese valence state (4+) are formed near vacancies in the antiferromagnetic matrix corresponding to the stoichiometric LaMnO 3. The relative volume of these regions and their average size (∼40 Å) were estimated from an analysis of the 55Mn NMR spectra.

Ladderlike ferromagnetic spin coupling network on a pi-conjugated pendant polyradical.

A poly(9,10-anthryleneethynylene)-based polyradical with two pendant stable phenoxyls in one anthracene skeleton was newly synthesized via polymerization of the corresponding bromoethynylanthracene monomer using a Pd(0) catalyst. The average molecular weight of the polymer reached M(n) = 5 x 10(3) and was soluble in common organic solvents. The polyradical was prepared from the corresponding hydroxyl precursor polymer and was appropriately stable at room temperature. The ESR spectrum of the corresponding monomeric radical suggested an effectively delocalized spin density distribution on the backbone anthracene. The magnetization and the static magnetic susceptibility of the polyradical were measured using a SQUID magnetometer. The large average spin quantum number (S = (5)/(2)) of the polyradical indicated that the ferromagnetic spin coupling network of the polyradical had spread throughout the pi-conjugated chain and that it was considerably insensitive to spin defects.

Electron-spin diffusion in proton-irradiation microstructured (fluoranthene)2PF6

The properties of the quasi-one-dimensional organic conductor (fluoranthene)${}_{2}{\mathrm{PF}}_{6}$ are modified by proton irradiation ${(E}_{p}=25\mathrm{MeV},$ ${n}_{p}=5.4\ifmmode\times\else\texttimes\fi{}{10}^{16}{\mathrm{cm}}^{\ensuremath{-}2}).$ The crystals are characterized by measurement of static magnetic susceptibility, cw--electron spin resonance, static magnetic-field gradient pulsed electron spin resonance and especially by one- and two-dimensional electron-spin-resonance imaging. Electron-spin diffusion constant parallel to the stacking direction is reduced by one order of magnitude, whereas the perpendicular direction remains essentially unchanged, for homogeneous proton irradiation. A well-defined periodic $100\ensuremath{-}\ensuremath{\mu}\mathrm{m}$ structure is impressed using appropriate metal grids in the proton beam. Thus the diffusion constant, as well as the concentration of localized defects, is spatially modulated. Experimental evidence of the coherence phenomena of the diffusing electron spins moving between the artificially created reflecting walls is presented.

Structural and magnetic properties of the alternating Heisenberg spin-chain compound dichloro(2,5-dithiahexane)copper(II)

Temperature dependence and anisotropy of the electron-spin-resonance (ESR) signal at 9.5 GHz of the one-dimensional alternating Heisenberg antiferromagnet dichloro(2,5-dithiahexane)copper(II) are reported in the temperature range between 5 and 300 K. The ESR measurements reveal a structural phase transition at ${T}_{c}$ $\ensuremath{\approx}150\mathrm{K}.$ By x-ray diffraction the structure of the low-temperature phase is determined at $T=120\mathrm{K}.$ Symmetry reduction from the monoclinic space group ${P2}_{1}/n$ to the triclinic group $P1\ifmmode\bar\else\textasciimacron\fi{}$ results in the formation of twin domains and the creation of two different kinds of spin chains below ${T}_{c}.$ The influence of the structural modifications on the magnetic properties is discussed in detail. Measurements of the static magnetic susceptibility yield the exchange constants and alternation parameters ${J}_{1}{/k}_{B}=\ensuremath{-}29.3(1)\mathrm{K},$ ${\ensuremath{\alpha}}_{1}=0.76(1)$ and ${J}_{2}{/k}_{B}=\ensuremath{-}27.9(1)\mathrm{K},$ ${\ensuremath{\alpha}}_{2}=0.99(1)$ of chain 1 and 2, respectively.