Zero-field paramagnetic resonance of trivalent gadolinium in several lanthanide tris(ethylsulfate) nonahydrates and nonadeuterates: Determination of crystal-field and hyperfine-structure parameters

Employing isotopically pure trivalent ¹⁵⁵Gd, ¹⁵⁷Gd, and ¹⁶⁰Gd as impurities in dilute mixed crystals of lanthanum tris(ethylsulfate) nonahydrate [La(C₂H₅SO₄)₃ ·{} 9H₂O], it has been possible to determine both accurate zero-field splitting parameters of crystal-field origin and hyperfine-structure constants due to magnetic dipole and electric quadrupole interaction terms. The zero-field paramagnetic-resonance spectroscopic method employed herein, has allowed the absolute signs of the hyperfine parameters to be determined. Thus the magnitude and sign of all diagonal parameters of the zero-field effective spin Hamiltonian are accurately known. It is reasoned that the quadrupole hyperfine constant is due, almost entirely, to lattice contributions; moreover, it is shown to be of the expected order of magnitude and sign. The hyperfine anomaly is discussed and is shown to be slightly less than the experimental error limits (three standard deviations). A set of crystal-field parameters are reported for the first time for ¹⁶⁰Gd in crystals of La(C₂H₅SO₄)₃ ·{} 9D₂O, which differ significantly from those of the hydrate. Variations of crystal-field parameters with various lanthanide host ions are also observed. Finally, a few comments concerning zero-field linewidths and their measurement are made.