Paramagnetic Transition Metal Research Articles

Magnetic Resonance of Paramagnetic Complexes

AbstractThe line width of the ESR and NMR signals of paramagnetic transition metal complexes is determined mainly by the electron spin‐lattice relaxation time τe. Values of τe greater than 10−9 lead to ESR spectra that are readily resolved, while values smaller than 10−11 give NMR spectra having small line widths. Since fast relaxation processes are effective in nearly all transition metal complexes with several unpaired electrons and in all complexes having an orbitally degenerate ground state, the NMR method has a wider scope. The sign and magnitude of the electron‐nucleus coupling can be determined with great sensitivity from the NMR spectra, whereas only the magnitude of this interaction can be determined from the ESR spectra. Free spin densities can be found very accurately from the NMR shifts, and the method can therefore be advantageously applied to kinetic measurements, e.g. on short‐lived contact complexes.

Synthesis and magnetic resonance studies of some paramagnetic transition metal aminotroponiminates

Synthesis and magnetic resonance studies of some paramagnetic transition metal aminotroponiminates

Magnetic moments in dilute transition metal alloys

Calculations are made of the total moment associated with transition impurities in ferromagnetic or paramagnetic transition metal hosts allowing for exchange enhancement on the host sites neighbouring an impurity. The model correctly predicts positive dμ/dc values when transition impurities to the right of iron in the periodic table are dissolved in Fe and the `giant moments' of PdFe, PdCo; it also explains the behaviour of PdCr as that of a `dwarf moment' with analogies to a Kondo bound state.

Exchange Enhancement of Spin Susceptibility in Strongly Paramagnetic Transition Metal Alloys : Breakdown of the Rigid-Band Model

The behavior of the magnetic susceptibility and the electronic specific heat of alloys of Ir with the other nearly filled d-band elements indicates that a rigid band model cannot be used to describe the behavior of the susceptibility. It appears that the large-susceptibility enhancement in these metals in mainly due to large intra-atomic interactions which, e.g., are large on Pt ions in pure Pt and remain large when a Pt ion is placed in Ir.

Magnetostriction of Paramagnetic Transition Metals and Alloys

Measurements of the longitudinal magnetostriction of transition metals and alloys in groups IV, V, VI, and VIII are reported. With the assumption that the magnetostriction is isotropic the volume-dependence of the magnetic susceptibility is evaluated. A theoretical estimate of the volume-dependence of the orbital susceptibility, ∂ lnχorb/∂ lnV≃1.5 (≃ electronic Gruneisen parameter), agrees well with the measured values for the group V metals. The group IV and VI metals appear to have a linear magnetostriction, though the field-independent susceptibility of a paramagnetic metal would indicate a quadratic magnetostriction as observed in the group V and VIII metals. The negative magnetostriction of Pd, Pt, and their alloys indicates that the exchange interaction decreases with increasing volume. But it is not possible to estimate theoretically the magnetostriction of these and other group VIII metals and alloys since too many unknown factors are involved. The emiprical relation between susceptibility and electron density also fails to predict correctly the magnetostriction.

Interpolation Scheme for Band Structure of Noble and Transition Metals: Ferromagnetism and Neutron Diffraction in Ni

A simple interpolation scheme for paramagnetic fcc transition and noble metals has been developed and extended to the ferromagnetic state of Ni. It is based on the representation of $d$ and conduction bands by linear combinations of atomic orbitals and orthogonalized plane waves, respectively, and includes hybridization effects through the use of k-dependent matrix elements. The energy bands of augmented-plane-wave calculations from first principles for Cu and paramagnetic Ni are fitted with an rms deviation of about 0.12 eV. The density of states of paramagnetic Ni is calculated and shown to be significantly influenced by hybridization. A self-consistent calculation of the ferromagnetic band structure of Ni is carried out by the incorporation of correlation effects through the use of an intra-atomic Coulomb interaction patterned along the lines suggested by Gutzwiller, Hubbard, and Kanamori. Experimental information relating to the magnetization, ferromagnetic Kerr effect, Fermi surfaces, neutron magnetic form factor, electronic specific heat, and high-field susceptibility is used to determine the parameters characteristic of the ferromagnetic state and to check the predictions of the resulting band structure. The k-dependent splitting of the bands averages 0.37 eV in the vicinity of the Fermi level. The wave functions resulting from these calculations are shown to be sufficiently realistic to permit the calculation of the total charge density in Cu and the magnetic form factor of Ni. The use of approximate spin-polarized wave functions appropriate to the solid demonstrates the importance of both unpaired and paired electrons to the magnetic form factor. The net conduction-electron polarization is found to be small and positive. The effective $s\ensuremath{-}d$ exchange energy changes sign between the central and outer parts of the Brillouin zone. The inclusion of spin-orbit effects is discussed, and the reduction of the density of states at the Fermi level due to this interaction is calculated. The effect is too small to explain the presence of ferromagnetism in Ni and its absence in Pd and Pt.

Ferromagnetic resonance in DNA samples

The aim of this work was to investigate the relationships between the chemical composition of oat grains and the tolerance to oxidative stress of oat genotypes. The studies were based on the results of biochemical analyses and both EPR and Raman spectroscopies on whole grains and their parts (embryo, endosperm, seed coat) originating from oat genotypes with different sensitivities to stress. We found that the amounts of fats and especially unsaturated fatty acids, proteins rich in glutamic acid and glycine, as well as phenolics and tocopherols were higher in grains of the tolerant genotype. Moreover, fats and proteins were distributed not only in embryos, but also in endosperms. The grains of tolerant genotypes exhibited high antioxidant activity and contained greater amounts of β-glucan. EPR data pointed to higher concentrations of various kinds of stable organic radicals (semiquinone, tyrosyl and carbon-centered radicals) in whole grains (and their parts) of sensitive genotypes. EPR spectra revealed the character of interactions of paramagnetic transition metal ions Fe(III) and Mn(II) with organic and inorganic structures of grains. The quantitative EPR measurements showed the dependence between the amount of radical species and the content of transition metal ions, mainly Fe(III) bonded to inorganic structures.

Investigation of the paramagnetism of μ-mesic atoms

The nature of the paramagnetism of various mesic atoms is investigated by measuring the asymmetry of (μ-e)-decay electrons. The results of the experiments indicate that paramagnetism of mesic atoms in dielectrics and diamagnetic and weakly paramagnetic normal metals is due to the magnetic moment of the μ-meson. In paramagnetic transition metals, lanthanides and actinides it is due to the magnetic moments of the electron shell and the meson. It is demonstrated that polarized mesons can be used as a means for investigating the magnetic properties of atoms and hydrides of the transition metals, actinides and lanthanides with zero nuclear spins.