Electric field gradient and magnetic hyperfine interaction at Eu nuclei in ferromagnetic EuS

The NMR spectra of 151Eu and 153Eu nuclei with the nuclear spin I = 5/2 were observed in ferromagnetic EuS using a single-crystal sphere by the cw method in fields up to 21 kOe below 4.2 K. In fields above magnetic saturation the 153Eu spectrum consists of quadrupole-split five lines whose relative intensities depend on field direction. The central-line frequency which gives a hyperfine field at nuclei exhibits a small anisotropy in good agreement with the previous results, but the frequency separation Δνq between the quadrupole multiplets is isotropic, which is determined to be 0.358 ± 0.005 MHz at 4.2 K. The temperature dependence of Δνq is rapid compared with that of the Eu magnetic moment. A linear extrapolation to absolute zero gives a value of Δνq = 0.422 ± 0.005 MHz which yields a quadrupole coupling of e2qQ/h = 2.81 ± 0.03 MHz. The 151Eu spectrum is a single line even in magnetic fields. (author)