Electron-Nuclear Double Resonance, Nuclear Moments, and <r-3> of Neodymium-143 (III) and Neodymium-145 (III) in Lanthanum Trichloride
The electron-nuclear double resonance (ENDOR) spectra of dilute solutions of trivalent Nd143 and Nd145 ions occurring at the La+3 ion sites in the axially symmetric LaCl3 structure have been measured at the temperature of boiling He. For laboratory fields of ~ 103 G the frequencies νn of the ENDOR transitions are in the range 10<=νn<=1000 Mc sec-1. The experimental results for each nuclide have been summarized by giving values of the parameters in the spin Hamiltonian, Hs=|β|H.g.S+S.T'.I+P'[Iz2-13I(I+1)]- βnH.gn'.I, which produce a rigorous least-squares fit to the data for the two experimental conditions H ⊥ c and H∥c, where c is a vector parallel to the hexagonal axis of symmetry of the LaCl3 crystal. The frequencies were fitted with rms deviations of 0.08δ for H∥c and 0.3δ for H ⊥ c, where δ is the average ENDOR line width, 3×105 cps. The gn' factor in the spin Hamiltonian was found to be anisotropic, with |gnII'gn⊥'|=0.62. A comprehensive theoretical interpretation of the spin Hamiltonian parameters using eigenvectors precisely calculated from the best available crystal field interaction parameters yielded μ(Nd143)μ(Nd145)=+1.60883+/-0.00004, μ(Nd143)=-1.079+/-0.06 nuclear magneton, μ(Nd145)=-0.671+/-0.04 nuclear magneton, Q(Nd143)Q(Nd145)=+1.96+/-0.2, Q(Nd143)=(+0.0206+/-0.003)×10-24 cm2, Q(Nd145)=(+0.0105+/-0.002)×10-24 cm2, <r- 3(Nd+3, 4f3)>=(36.9+/-4.5)×1024 cm-3. An upper limit of one part in two thousand was established for the contribution, if any, of a contact term to the hyperfine interaction. The errors quoted are estimated standard deviations of the mean based upon internal consistency. A discussion of the errors and their sources is given. In particular, the precision of the determination of the nuclear moments μ and Q, of <r-3>, and of the contact term was limited mainly by the inaccuracies of the best available values of the crystal field parameters Anm<rn>. Numerical values of the spin Hamiltonian parameters, crystal field eigenvectors, and relevant interaction multiplicative factors are tabulated.