Electron-Paramagnetic-Resonance Absorption by Trivalent Neodymium Ions in Single Crystals of Lanthanum Trichloride and Lanthanum Ethyl Sulphate in Zero Magnetic Field

Measurements of magnetic-dipole transition frequencies of 143,145Nd³⁺ occurring substitutionally for La³⁺ in LaCl₃ were made for the first time in the absence of an external magnetic field. The sensitive [10¹³ spins/ (Mc/sec linewidth)], versatile, cavity-type, variable-frequency (1000-4600 Mc/sec) spectrometer developed for these experiments is described. Measurements of magnetic-dipole transition frequencies of 143,145Nd⁺³ in La(C₂H₅SO₄)₃·{}9H₂O made at low field by Bleaney were repeated at zero magnetic field. The results are summarized in terms of a least-squares best fit of the spin Hamiltonian H=ASzIz+B(SₓIₓ+SyIy)+P[Iz²-1/3I(I+1)] to the data. The spin-Hamiltonian parameters are independent of temperature between 4^∘{} and 15^∘{}K. Theoretical interpretation of the spin-Hamiltonian parameters yielded ¹⁴³μN¹⁴⁵μN=1.60892±0.00010, ¹⁴³gₙ〈r^-3〉=(11.59±0.10)×10²⁴ cm^-3, and ¹⁴³μN=(1.10±0.10) nm for the LaCl₃ crystal; and ¹⁴³μN¹⁴⁵μN=1.60886±0.00029, ¹⁴³gₙ〈r^-3〉=(11.56±0.10)×10²⁴ cm^-3 and ¹⁴³μN=(1.10±0.10) nm for the La (C₂H₅SO₄)₃·{}9H₂O crystal assuming 〈r^-3〉=(36.9±4.5)×10²⁴ cm^-3. The close agreement of gₙ〈r^-3〉 for the two crystals implies that 〈r^-3〉 is independent of the host for these two crystals.