Paramagnetic Susceptibility Measurements Research Articles

Electron paramagnetic resonance and magnetic susceptibility studies of dimanganese concanavalin A. Evidence for antiferromagnetic exchange coupling.

The double Mn2+ complex of concanavalin A with bound saccharide (SMMPL) was examined by electron paramagnetic resonance (EPR) spectroscopy and magnetic susceptibility measurements. A room temperature X-band (9 GHz) EPR spectrum of SMMPL revealed a relatively weak, broad resonance in contrast to the spectrum with a six-line hyperfine-split pattern observed for the mononuclear, high-spin Mn2+ complex found in Ca2+-Mn2+-concanavalin A with saccharide present (SCMPL). The EPR spectrum of SMMPL at 77 K, however, consisted of a series of overlapping patterns of 11 hyperfine-split lines near g = 2.0 with members of each pattern separated by 47 G, half the value of the hyperfine splitting of SCMPL. These 11-line patterns are preserved at Q-band (35 GHz), indicating that the manganese ions in SMMPL form a spin-coupled, binuclear center. As expected for an exchange-coupled system, the EPR signal of SMMPL at 77 K saturates at a higher microwave power than those for SCMPL or Mn2+ aquoion. There is also a marked loss of EPR signal intensity for SMMPL between 4.2 and 1.4 K, which supports the view that the pair of manganese ions is exchanged-coupled. The temperature dependence of both the magnetic susceptibility and the low-temperature EPR spectral intensity can be explained by a model in which the two high-spin Mn2+ ions of SMMPL are antierromagnetically exchanged-coupled with an isotropic coupling constant J = 1.8 cm-1 (for the spin Hamiltonian Hex = JS1.S2). Zero-field splitting D' was estimated to be 375 G from the EPR spectrum.(ABSTRACT TRUNCATED AT 250 WORDS)

Magnetic properties of Ba 2SmCu 3O 9−x high T c superconductor

The magnetic properties of the new high T c superconductor Ba 2SmCu 3O 9−x have been investigated from DC magnetization measurements performed in a SQUID magnetometer. The amount of Meissner effect at low temperature is 35% of the full diamagnetic flux expulsion thus indicating bulk superconductivity. The lower critical field at 4.8 K is H c1 = 170 ± 20 Oe and the upper critical field is much higher than 55 KOe. Paramagnetic susceptibility measurements give an effective magnetic moment for Sm 3+ slightly lower than the free ion value.

Synthesis, characterization, and magnetic properties of mixed-valence europium-ammonia intercalation compounds of titanium disulfide

Europium-ammonia intercalation compounds of titanium disulfide have been synthesized by reaction of EuNH 3 solutions with TiS 2, characterized by thermogravimetric analysis and powder X-ray diffraction, and investigated by electron paramagnetic resonance, magnetization, and magnetic susceptibility measurements. These materials crystallize in a 3 R-type structure in which every layer is occupied by intercalated species. The intercalation of NH 3 is accompanied by the formation of NH + 4 until a critical electron concentration of 0.22 mole el/mole TiS 2 have been transferred to the TiS 2 conduction band. Although Eu 3+ is the predominant Eu species for x > 0.001, Eu 2+ is also formed, possibly from the reduction of Eu 3+ in the van der Waals gap. These mixed-valence compounds are best described by the formulas (Eu 3+) x′ (Eu 2+) x″ (NH + 4) y′ (NH 3) y″ TiS (3 x′+2 y″+ y′)− 2 for 3 x′ + 2 x″ + y′ < 0.22 and (Eu 3+) x′ (Eu 2+) x″ (NH 3) y″ TiS (3 x′+2 x″)− n2 for 3 x′ + 2 x″ ≥ 0.22.

Crystal field effects in TmCu2 compound

The splitting of the3H6 multiplet has been estimated for the Tm3+ ion in the crystal electric field of the orthorhombic TmCu2 compound. Using the energy levels and appropriate eigenfunctions the crystal field only susceptibility has been calculated along the principal orthorhombic axes at temperatures 10 to 300 K. The obtained results are compared with our measurements of specific heat and paramagnetic susceptibility on polycrystalline sample.

Study of intradimer and interdimer exchange interactions in dichlorobis(diethylenetriamine)dicopper perchlorate ([Cu2(dien)2Cl2](ClO4)2) by electron paramagnetic resonance and magnetic susceptibility measurements

Study of intradimer and interdimer exchange interactions in dichlorobis(diethylenetriamine)dicopper perchlorate ([Cu2(dien)2Cl2](ClO4)2) by electron paramagnetic resonance and magnetic susceptibility measurements

Approximate D4d symmetry of the cation site in hexahydrated trichlorides of rare earths and actinides

Abstract Many spectroscopic and magnetic properties of the monoclinic hexahydrated chlorides of rare earths have been shown to approximate those of a uniaxial crystal. We explain this approximate symmetry by the shape of the coordination polyhedron of the rare-earth ions which is approximately that of a square antiprism of D4d symmetry, with an inverse eightfold axis. The directions of this axis and of the spectroscopically or magnetically determined axes agree well. The absence of MJ mixing for some levels, as observed in the Zeeman effect, can be explained by an eightfold axis. As a first approximation, we propose a study of the magnetic ions using a D4d crystal field hamiltonian with the limited set of even parameters B02, B04 and B06; polarization and intensity spectral data, Zeeman effect, electron paramagnetic resonance and susceptibility measurements can be interpreted in this symmetry. Such remarks also apply to actinide hexahydrated chlorides.

Molybdenum(V) Chloride Complexes with Aliphatic Diamines

Abstract For the first time it has been possible to prepare complexes of Mo(V) with the following aliphatic diamines: 1,2 ethylenediamine (en), 1,3 trimethylenediamine (tn), 1,4 tetramethylenediamine (bn), 1,5 pen-tamethylenediamine (pn), 1,6 hexamethylenediamine (hn) and 1,8 octame-thylenediamine (on). Analytical results show that all the complexes prepared correspond to the empirical formula [Mo2Cl2(AA)8] Cl8 where AA is the diamine. The measurement of paramagnetic susceptibilities underlines the diamag-netic nature of all the compounds. Thermogravimetric studies reveal very similar behaviour in all cases with the final formation of MoO3. According to i.r. spectra, diamines act as monodentate ligands, and the Moatoms are bridged through chlorine ligands. Electronic spectra show no bands in the visible region.

Mo(V) Dimer Complexes with α, ω-Aliphatic Diamines. II. Long Chain Ligands

Abstract The Mo(V) complexes with the following aliphatic compounds, 1,9 nonanediamine (nn) and 1,10 decanediamine (dn), have been prepared according to a modified procedure described in a previous paper. Analytical results revealed the two complexes obtained had a stoichiometry of [Mo2Cl2(AA)4] Cl8, with AA as the diamine. The paramagnetic susceptibility measurements suggest the diamagnetic nature of the two compounds. Both complexes behaved similarly in thermogravimetric studies, and in both cases the processes resulted in the formation of MoO3. The i.r. spectra showed that the diamines act as bidentate ligands and it is suggested that the molybdenum atoms are bridged through chlorine ligands. No bands were seen in the visible zone of the electronic spectra.

Synthesis and Characterization of Fe(III) and Cr(III) 4-Hydroxy-3-Nitro-Phenylarsonates

Abstract Fe(III) and Cr(III) salts of 4-hydroxy-3-nitro-phenylarsonic acid (H2A), having the formulae Fe(HA)3, Fe2A3, Cr(HA)3 and Cr(A)(OH) were synthesized. Based on IR and reflectance spectral data, paramagnetic susceptibility measurements ans solubility data, the cations are postulated to be in an octahedral environment.

Metal thiolate clusters in cobalt(II)-metallothionein.

Rabbit liver metallothionein-1 in which all seven metal-binding sites are occupied by cobalt(II) exhibits spectral features typical of tetrathiolate coordination with approximate Td microsymmetry [Vasák, M. (1980) J. Am. Chem. Soc. 102, 3953-3955]. With a total of 20 cysteine residues per molecule, this mode of metal binding implies that some of the thiolate ligands are shared by neighboring Co(II) ions, resulting in clustered structures. In this study, evidence for the existence of thiolate-linked Co(II) clusters is presented and their mode of formation is explored by comparing the optical and magnetic properties of forms of Co(II)-metallothionein containing 1-7 equivalents of Co(II). Preparations with up to 4 Co(II) equivalents display electronic spectra in the d-d and charge-transfer regions that resemble those of isolated tetrahedral Co(II)-tetrathiolate complexes. Upon binding of more than four Co(II) ions, however, the spectrum changes progressively and approaches in the fully saturated Co(II)-metallothionein an absorption profile similar to that of crystallographically defined model (Co)II-tetrathiolate clusters [Dance, I. G. (1979) J. Am. Chem. Soc. 101, 6264-6273]. These effects are closely paralleled by changes in the ESR spectrum. Above 4 Co(II) equivalents per thionein, the ESR signal at gx approximately 5.9 measured at 4 K decreases progressively in intensity, until in the fully occupied protein the complex is nearly diamagnetic. These changes, which were confirmed by measurements of paramagnetic susceptibility, establish the existence of Co(II) thiolate clusters in Co(II)-metallothionein. The loss of paramagnetism reflects most likely antiferromagnetic coupling of neighboring Co(II) ions brought about by a superexchange mechanism via the thiolate bridging ligands.

Magnetic Properties of Tb–Er Single Crystal Alloys

Measurements of ac initial susceptibility, magnetization and paramagnetic susceptibility have been made along the principal axes of Tb–Er single crystal alloys. It is found that the magnetic structures of cone, tilted helix, flat helix and basal plane ferromagnet appear at 4.2 K in the sequence of increasing Tb concentration in this system. The tetracritical point showing a coexsistence of CAM, mixed CAM, helix and paramagnet is observed at 87 K for Tb 0.05 Er 0.95 alloy. From the analyses of the Neel temperatures and the anisotropic paramagnetic Curie temperatures, the exchange interactions J (Q), J (O) and the magnetocrystalline anisotropy K 2 para 0 in the paramagnetic state were estimated on the basis of the molecular field theory.

Paramagnetic state NMR and susceptibility measurements in cobalt based Heusler alloys

Susceptibility of Co2TAl (T Ti, Zr and Hf) and 59Co and 27Al Knight shifts have been measured down to the magnetic ordering temperature of these itinerant ferromagnets. The effective hyperfine fields per Bohr magneton at Co and Al nuclear sites have been derived and for Co these are in very good agreement with the spin echo results in ferromagnetic state of these alloys. The effective fields at Al site are small which is the reason that no spin echo signal due to Al could be observed. The sign of the field at Al site is accounted for in terms of an RKKY model of conduction electron polarization with appropriate preasymptotic correction.

Magnetic, transport, and thermal properties of ferromagnetic EuB6

Magnetic measurements on Al-flux grown EuB6 crystals show that this material orders ferromagnetically with a transition temperature Tc=13.7 K. The effective moment derived from paramagnetic susceptibility measurements gives μeff=7.76 μB, and the saturation magnetization extrapolated to 0 K is within 10% of the theoretical value of 7 μB expected for Eu+2. The magnetic order, however, cannot be that of a simple colinear ferromagnet because the magnetic specific heat in zero applied magnetic field shows a broad maximum centered about 9 K rather than the expected λ-like anomaly at 13.7 K. Finally, transport measurements suggest that EuB6 is an intrinsic semimental.

Ligating properties of model bioheterocyclics—I: Complexes of copper(II) and cobalt(II) halides with 3,6-disubstituted-2,7-dihydro-1,4,5-thiadiazepine derivatives

Copper(II) and cobalt(II) halides react with 3,6-disubstituted-2,7-dihydro-1,4,5-thiadiazepine derivatives(L) to form highly hygroscopic complexes of the general formulae, [(CuCl 2) 2L] 2nH 2O; [(CuBr 2) 3L 2]nH 2O and [CoX 2L] 2nH 2O respectively. On the basis of analytical, reflectance, paramagnetic susceptibility and molar conductance measurements, Cu(II) chloride and bromide complexes have been assigned dimeric and monomeric structures in which bridging through halogens and thiadiazepine ring takes place. These complexes are mixtures of stereoisomeric forms of square planar and distorted tetrahedral geometries. Co(II) complexes have been shown to possess tetrahedral geometry with dimeric structure in which bridging through only thiadiazepine ring occurs. Thermal stabilities, IR and PMR data is also reported. Here L acts as a bridging bidentate ligand by coordinating through two adjacently placed nitrogen atoms.

Crystal fields at light rare-earth ions in Y and Lu

Crystal-field parameters have been deduced for the light rare-earth solutes Ce, Pr, and Nd in Y or Lu hosts from measurements of the paramagnetic susceptibilities. In the analysis all multiplets in the lowest $\mathrm{LS}$ term were included. For a given host, crystal-field parameters divided by Stevens factors $\frac{{B}_{\mathrm{lm}}}{{\ensuremath{\alpha}}_{l}}$, are of approximately the same magnitude for all the solutes Pr, Nd, Tb, Dy, Ho, Er, and Tm and do not scale with $〈{r}^{l}〉$. The values deduced for Ce do not fit in with this simple picture. The higher-order parameters ${B}_{40}$, ${B}_{60}$, and ${B}_{66}$ are, within the errors in their determination, identical in Y and Lu hosts, indicating that these values for a specific rare-earth solute in Y and Lu may give a reliable estimate for the corresponding sites in rare-earth metal. This is confirmed for Pr, for which these values and the value of ${B}_{20}$ deduced from paramagnetic-susceptibility measurements on the pure metal, correctly explain the transition observed by neutron spectroscopy and the level crossing observed in a high-field experiment. A weighted average of ${B}_{20}$ for cubic and hexagonal sites in Nd and Sm was obtained from the paramagnetic susceptibilities of these metals at high temperatures.

Molecular-field coefficients of rare-earth iron garnets

Molecular-field coefficients of several rare-earth iron garnets (Tb, Dy, Ho, Er, and Yb) have been determined by fitting calculated-and-experimental magnetic-moment–vs–temperature curves. For these compositions, spin canting appears to cause a significant reduction in the net moment of the c sublattice. The results are compared with values of coefficients derived from paramagnetic susceptibility measurements and with other values determined without taking into account c-sublattice canting.

Proprietes magnetiques de l'oxyde Eu 2O 3 monocristallin

Single crystals of europium oxide Eu 2O 3 with monoclinic B structure were prepared by the Verneuil process. The magnetic properties of these crystals have been studied. Paramagnetic susceptibility measurements have been performed for various orientations of the crystal with respect to the magnetic field at constant temperatures (5,77 and 300 K) as well as at increasing temperatures (5 – 1000 K). They show an anisotropy. An interpretation of this phenomenon is proposed.

Exciton Dynamics Study by Magnetic Resonance in TCNQ− · NH

AbstractThe tetracyanoquinodimethan salt TCNQ− NH belongs to the low conductivity class. It is a simple salt, the two partly deuterated salts TCNQ− · ND and TCNQD · NH can be easily prepared. A substantial amount of information has been gathered concerning the magnetic resonance of these salts: electron spin resonance, dynamic nuclear polarization, and spin‐lattice relaxation. Thus it was possible to study the relaxation mechanisms in this particular case. The experimental results can be interpreted, above the transition temperature, in terms of the model of Frenkel spin excitons; this model introduced by Soos is in good agreement with paramagnetic susceptibility measurements. It is shown that the excitons are localized in the TCNQ chains and have the dynamics of a one dimensional triplet exciton system.

Elaboration et proprietes magnetiques de monocristaux d'oxyde de praseodyme Pr 2O 3

Single crystals of praseodymium oxide with hexagonal A structure were prepared by the Verneuil process. Paramagnetic susceptibility measurements have been performed for various orientations of the crystal with respect to the magnetic field at constant temperatures (5, 77, 300°K) as well as at increasing temperatures (5–1000°K). They show an exceptional magnetic anisotropy ( χ ⊥ χ ∥ ⋍ 12 at 5°K). An interpretation of this phenomenon is proposed.

Electron spin resonance study of metallic lithium–ammonia systems

Electron spin resonance (ESR) in metallic lithium−ammonia systems has been investigated in the temperature range 12−296°K. In the liquid solutions and in the cubic phase of Li(NH3)4 the conduction−electron−spin resonance (CESR) line shapes are in excellent agreement with Dyson’s theory. The g shift, which is independent of concentration and temperature, is equal to 7.9±0.3×10−4. The spin−orbit coupling constant derived from the g shift is about 10 cm−1. The diffusion time TD is nearly independent of temperature in the liquid state, but it is strongly dependent on concentration and undergoes a fourfold decrease at the freezing point of Li(NH3)4. The spin−lattice relaxation time T1 is weakly dependent on concentration and temperature in the liquid state and undergoes a twofold increase at the freezing point of Li(NH3)4. The data are consistent with the spin−orbit relaxation mechanism and indicate that to a good approximation the solvated ions are the only spin scatterers in the liquid state. The paramagnetic susceptibility of liquid Li(NH3)4 is independent of temperature and equal to 77×10−6 emu/mole. For metallic concentrations below 18 MPM the cubic phase is found below the solid−solid transition temperature, and the relative amount of the cubic phase present increases with decreasing lithium concentration. An ESR signal is also observed in the hexagonal phase of Li(NH3)4. Paramagnetic susceptibility measurements indicate that the hexagonal−phase ESR signal is due to localized moments which appear near the solid−solid transition temperature. The reciprocal paramagnetic susceptibility varies linearly with temperature down to 30°K, shows a broad minimum between 20 and 30°K, and increases below 20°K. No resonance signal could be detected below 12°K. The paramagnetic susceptibility of hexagonal−phase Li(NH3)4 at 54°K is about 1.5×10−6 emu/mole. The results indicate that the concentration of localized moments is small and they order antiferromagnetically below 20°K. The Fermi surface in the hexagonal phase is re−examined on the basis of the spin−orbit coupling constant determined from g shift measurements.