Quadrupole Coupling and Knight Shift Anisotropy in "hcp" Lanthanum

The nuclear magnetic resonance of La¹³⁹ has been observed in hcp polycrystalline lanthanum metal at 25.6 kOe and 300^∘{}K. The recorded pattern at 15.5 Mc/sec displays a central line and one pair of satellite lines. The position and shape of the central line yields an isotropic Knight shift of (0.685±{}0.020)% and an axial shift of (0.046±{}0.020)%. The satellite spacing yields a lowest pure quadrupole frequency νQ=101±4 kc/sec or e²qQh=(1.41±0.06) Mc/sec. A calculation of the lattice electric field gradient is made for the ABAC stacking sequences, yielding 0.540×{}10²² and 0.487×{}10²² cm^-3 for the so-called A and B (or C) layer sites, respectively, by the method of plane-wise summation of de Wette. Improved values of the nuclear electric quadrupole moment, Q(La¹³⁹)=0.21 b, and the Sternheimer antishielding factor, γ_∞(La³⁺)=-73.5, are adopted and discussed. The sign of the conduction-electron electric field gradient is shown to be negative.