Electric Field Gradient and Magnetic Hyperfine Interaction at Eu Nuclei in Ferromagnetic EuS

Abstract

The NMR spectra of 151 Eu and 153 Eu 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 153 Eu 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 Δν q between the quadrupole multiplets is isotropic, which is determined to be 0.358±0.005 MHz at 4.2 K. The temperature dependence of Δν q is rapid compared with that of the Eu magnetic moment. A linear extrapolation to absolute zero gives a value of Δν q =0.422±0.005 MHz which yields a quadrupole coupling of e 2 q Q /h=2.81±0.03 MHz. The 151 Eu spectrum is a single line even in magnetic fields.