Axis Of Electric Field Gradient Research Articles

Mössbauer Effect in Iron-Nitrogen Alloys and Compounds

Mossbauer effects of 57 Fe in iron-nitrogen martensite and its tempering stages were measured. The spectra were resolved into the components corresponding to the 1st, 2nd, 3rd, 4th and farther n n Fe for each interstitial nitrogen atom. The analysis showed the localized perturbations by the nitrogen atoms on a host iron lattice similar to the case of iron-carbon martensite. 2) The principal axis of electric field gradient at the 2nd n n Fe in the α''-Fe 16 N 2 were determined to be directed to the nitrogen atom, not being parallel to the c -axis. The number of s and d electrons for the 1st n n Fe in some iron-nitrogen compounds were determined. The reduction of internal field, larger for interstitial alloys and compounds relative to substitutional ones, was proportional to the coordination number, n , to the neighboring nonmetal atoms. While, the variation of isomer shift depended upon both n and nonmetal concentration c .

A Mössbauer Study of a Sn-119 Bearing Solute in an Ordered Smectic Liquid Crystal, at 77°K

Abstract An ordered solute “monocrystal” was obtained by dissolving 3.5-7.0% (by weight) of triethyltin palmitate (3EtSnPalm) into 4-n-hexoxybenzylidene-4′-n-propylaniline and cooling from 90°C to room temperature through the nematic and semectic A phases to the smectic H phase (T < 60°C) in a magnetic field of 9000 Gauss. The disc-shaped sample was then removed from the magnetic field and cooled to 77°K at which temperature the Mossbauer measurements were made. From the variation of the area ratio of the two quadrupole split Mossbauer absorption peaks as a function of the angle between the orienting magnetic fields and the γ-ray beam we have determined the sign of the axial electric field gradient (Vzz) at the tin site in 3EtSnPalm to be positive. Further, the theoretical fit to the data yielded the solute order parameter, S = 0.17 and the molecular contribution to the nuclear vibrational anisotropy for the tin atom in the 3EtSnPalm molecule, ϵM = - 0.8. An independent value of ϵM = -1.50 was obtained fr...

Electron Relaxation of Fe Ion in Antiferromagnetic Cobaltous Carbonate

A M\"ossbauer study of CoC${\mathrm{O}}_{3}$ doped with ${\mathrm{Fe}}^{57}$ was made above and below the N\'eel temperature. The magnetic hyperfine field at ${\mathrm{Fe}}^{57}$ nuclei below ${T}_{N}$ is observed to be perpendicular to the principal axis of the maximum electric field gradient. Asymmetric line broadening at low temperatures was observed and interpreted in terms of spatial distribution of the average magnetic hyperfine field over the nuclear observation time. $H=72\ifmmode\pm\else\textpm\fi{}2$ kG and $\frac{1}{2}{e}^{2}\mathrm{qQ}{(1+\frac{1}{3}{\ensuremath{\eta}}^{\ensuremath{'}2})}^{\frac{1}{2}}=1.95\ifmmode\pm\else\textpm\fi{}0.04$ mm/sec at 4.9\ifmmode^\circ\else\textdegree\fi{}K were observed.

14N nuclear magnetic resonance of some solid nitrates

The equations of the “moment method” of Brown and Parker have been modified so that single crystals can be studied without prior knowledge of the orientation of the principal electric field gradient axes at the nuclei in question in the magnetic field. In addition, the equations have been applied to powdered substances. Single crystals of uranyl nitrate hexahydrate and rubidium uranyl nitrate were investigated by obtaining nuclear magnetic resonance spectra of the 14N nuclei in these species. Nuclear electric quadrupole coupling constants and asymmetry parameters of the nitrogen nuclei as well as the orientation of the nitrate groups with respect to the crystallographic axes were determined. Interpretation of these results indicate that the structure of uranyl nitrate hexahydrate is that reported by Flemming and Lynton with slight modification of the nitrate positions. Also, these results show that the two crystal “habits” of rubidium uranyl nitrate are not different habits but are actually different crystal structures. Powdered samples of anhydrous zinc, cadmium and mercuric nitrates were also investigated by 14N NMR. The results indicate that the nitrates in zinc and mercuric nitrate are bidentate while in cadmium nitrate they are ionic or very nearly so.

Determination of Spin Directions and Electric Field Gradient Axes in Vivianite by Polarized Recoil‐Free γ‐Rays

AbstractNon‐polarized and linearly polarized recoil‐free γ‐rays (Mössbauer effect) have been used to determine spin directions and the orientation of the electric field gradient (EFG) principal axes for the two iron sites in vivianite. The values obtained for the internal fields, quadrupole splittings, isomer shifts, and the relative orientations of the internal fields and EFG principal axes with respect to the crystal axes are tabulated.

Zeeman Quadrupole Spectrum of Cyanuric Chloride

Zeeman splitting studies of the Cl35 pure quadrupole resonances in cyanuric chloride have been carried out. Location of the principal electric field gradient axes demonstrated that cyanuric chloride is a planar molecule, with a threefold rotation axis perpendicular to the molecular plane. The planar molecules all lie in the (1, 0, 1) planes of the monoclinic crystal. It seems likely that the molecules are oriented within these planes so that each molecule has a carbon-chlorine bond lying along the b crystallographic axis. The field gradient asymmetry parameter is 0.24 for all the Cl atoms. This result is interpreted in terms of the effect of the ring nitrogens on the double-bond character of the carbon-chlorine bond.

Free Magnetic Induction in Nuclear Quadrupole Resonance

The free precession of an ensemble of nuclear quadrupole moments in an axial electric field gradient is studied by the pulsed nuclear induction method. A quantum-mechanical analysis describes the free precession and spin echo signals which result from the application of single and double pulses of radio-frequency field at the condition of zero-field quadrupole resonance. Beat modulation effects exhibited by free precession signals in a small constant external magnetic field are predicted by analysis. An alternative semiclassical description of quadrupole precession is given, which is analogous to the macroscopic nuclear induction equations of Bloch. Theory is verified by observation of free precession signals of chlorine in NaCl${\mathrm{O}}_{3}$.

Nuclear Resonance ofNb93in KNbO3

The nuclear resonance of ${\mathrm{Nb}}^{93}$ in a single crystal of KNb${\mathrm{O}}_{3}$ has been studied in magnetic fields of approximately 5000, 100, and zero oersteds, and at temperatures between -196\ifmmode^\circ\else\textdegree\fi{}C and +460\ifmmode^\circ\else\textdegree\fi{}C. The quadrupole splitting of the magnetic resonance line in strong fields is found to be a sensitive function of crystal structure and, hence, of temperature. Temperatures of the phase transitions found in this way at about -50, +220, and +430\ifmmode^\circ\else\textdegree\fi{}C are in agreement with other known data for this substance. The splitting $\ensuremath{\Delta}\ensuremath{\nu}$ of one satellite line is a continuous function of temperature between 220 and 430\ifmmode^\circ\else\textdegree\fi{}C; near 430\ifmmode^\circ\else\textdegree\fi{}C $\ensuremath{\Delta}\ensuremath{\nu}$ changes abruptly, indicating a first-order phase change. Below the Curie temperature (430\ifmmode^\circ\else\textdegree\fi{}C) KNb${\mathrm{O}}_{3}$ is ferroelectric, with noncubic crystal structure. Above 430\ifmmode^\circ\else\textdegree\fi{} it is cubic and a single resonance line is observed.Four lines have been identified in the pure quadrupole spectrum in zero magnetic field, and at 20\ifmmode^\circ\else\textdegree\fi{}C. From the four frequencies the quadrupole coupling constant and asymmetry parameter are evaluated to be 23.1 Mc/sec and 0.80, respectively. At -196\ifmmode^\circ\else\textdegree\fi{}C, the frequencies are different from the room temperature values, and the quadrupole coupling is evaluated to be 16.0 Mc/sec and the asymmetry parameter 0.0, the latter appropriate to the rhombohedral crystal structure at this temperature. The Zeeman effect in magnetic fields up to about 100 oersteds is shown to be an aid in identifying the absorption lines and in locating the principal axes of the crystalline electric field gradient. The value of the quadrupole coupling constant is consistent with the existence of a strong covalent character in the chemical bonding to the Nb.