Low-symmetry Field Research Articles

On the spin equilibrium in bis(2,2′,2″-terpyridine) cobalt(II) salts

The magnetic behavior of salts of the bis(2,2′,2″-terpyridine)Co(II) cation with seven different anions has been studied over the range 15-400°K. The temperature dependence of the moment is found to be dependent on both the anion and the degree of hydration. It is suggested that low symmetry field components are very important in determining the behavior. The electronic spectra have been studied at 77 and 300°K and data are reported.

Ionic energy levels in trigonal and tetragonal fields

The aim of this paper is that of finding the ionic energy levels in an electric field, if in addition to this field the ion is acted upon by a field of lower symmetry, in our case crystalline fields of trigonal or tetragonal type. Following the work of Bethe, and the work of Schönfeld on the cubic field, we shall reduce the representations of the cubic group, by restricting to its trigonal and tetragonal subgroups, and then utilizing the technique developed by Racah, we shall be able to write down the field matrices for every irreducible representation of the trigonal and the tetragonal groups. In this paper we shall consider only the electronic configurations d 2 and d 3, but it must be mentioned that the same technique can be applied to other electronic configurations, assuming that the cubic splitting in these configurations is already known.

Electron Spin Resonance and Optical Spectra ofV2+in NaCl

The ESR and optical spectra of ${\mathrm{V}}^{2+}$ in NaCl show that there are two species of ${\mathrm{V}}^{2+}$, one of which is situated in a tetragonal and another in an orthorhombic site. Optically, three weak bands corresponding to transitions between Stark levels and one strong electron-transfer band were detected which yield the crystal field strength $\ensuremath{\Delta}=8190$ ${\mathrm{cm}}^{\ensuremath{-}1}$ and the Racah parameter $B=559$ ${\mathrm{cm}}^{\ensuremath{-}1}$. Two long-wavelength bands show some structure which is probably due to splitting by low-symmetry fields. The $g$ shift and zero-field splitting of the center in the tetragonal site suggest that the $d$ orbitals are considerably distorted by covalency.

Crystal Spectrum and Magnetism of Tetrakis-Thiourea-Nickel Chloride

The polarized crystal spectrum of tetrakis-thoiurea-nickel chloride has been determined. The molecular symmetry is C4v; however, the results indicate that the absorptions arise from a field of lower symmetry, since in C4v symmetry the observed ``parallel'' absorptions would be orbitally forbidden. The intensity of the parallel absorptions are explained by a vibronic mechanism in which vibrations of the proper symmetry give allowed character to forbidden transitions under the site symmetry C4 Factor group interaction may also, at least in part, be responsible for the parallel intensity. The agreement between the assigned transitions and theory for nickel complexes is good assuming a reduction of the Slater—Condon parameters. The magnetic susceptibility of the complex follows a Curie—Weiss law χ=1.14/(T+6°) between 77° and 370°K.

Studies of the Optical Absorption Spectrum of an Interstitial Co++Ion in KCl Crystals

The optical absorption spectrum of the interstitial Co ++ ion in KCl observed by Nasu and Kuwabara is studied theoretically in the framework of the crystalline field theory. The crystalline field parameters D q and B are determined ( D q =325 cm -1 , B =734 cm -1 ). The absolute value of the oscillator strength of the visible absorption peak is calculated, by using Van Vleck molecular orbital model. The calculated f value by using the 3 d and 4 p orbitals of the Co ++ ion and the σ orbitals of the ligands is in good agreement with the experiment. In this case, the Co ++ 4 p orbitals which are admixed with the 3 d orbitals play an important role in the intensity. The mixing ratio of the 4 p orbitals determined from the observed f value is about 0.35. If K + vacancies are present near the Co ++ ion, this value can be obtained by the perturbation due to the crystalline field of lower symmetry, but if the symmetry of the crystalline field is tetrahedral, such a large value cannot be obtained.

Origin of the Magnetic Anisotropy Energy of Cobalt Ferrite

The magnetic anisotropy of cobalt ferrite is considered to arise from the cobaltous ions in the crystalline field of a low symmetry. The crystalline field due to the averaged-out charge distribution of C02+ and Fe3+ ions in the octahedral sites gives the lowest-lying twofold degenerate orbital level of the C02+ ion and to this level are associated four spin levels, corresponding to 8=3/2, as each spin is subject to exchange field. Each of these orbitally doubly degenerate levels is further split into two by the low symmetry field arising from the difference of charges of C02+ and Fe3+ ions and spin-orbit coupling. The magnitude of this energy splitting depends on the direction of the exchange field, thus on the direction of the magnetization, and from this origin the anisotropy energy arises. The relation between the magnitude of the anisotropy energy and the strength of the low symmetry field is discussed. Two kinds of configuration, A and B, of the C02+ and Fe3+ ions neighbouring each C02+ ion are considered as having low energy values. By properly choosing the relative numbers of C02+ ions in these A and B configurations and the strengths of the respective low symmetry fields, the calculated temperature dependence of the cubic anisotropy constant Kl can be fitted with that measured by Shenker. The values of the parameters thus determined seem to be reasonable, as they can be compared with those calculated on the assumption of the point charge model. The magnetic moment consisting of the spin and orbital moments is calculated to be 3.4~3.5 J1.g per C02+ ion. Finally, the dependence of the anisotropy constant of the mixed Fe-Co ferrite on the concentration of the cobaltous ions is discussed.

Erratum: “On the Absorption Spectra of Complex Ions IV. The Effect of the Spin-orbit Interaction and the Field of Lower Symmetry on d electrons in Cubic Field”

Erratum: “On the Absorption Spectra of Complex Ions IV. The Effect of the Spin-orbit Interaction and the Field of Lower Symmetry on d electrons in Cubic Field”