Cu63NMR studies of copper sulfide

Abstract

We have measured the $^{63}\mathrm{Cu}$ NMR of powdered copper sulfide CuS, in the region between 1.5 K and a room temperature, under magnetic field up to 6.5 T. An intense resonance peak and its satellites have been observed at all of the measured temperatures. The intense peak consists of two resonance lines above 60 K, and four lines below about 50 K. The splitting corresponds to the reported crystalline distortion and anomaly in specific heat below 55 K. There are complex satellites around the central intense peak, which are attributable to the first- and second-order quadrupole splittings. The Knight shifts of the central intense peak are nearly temperature independent and range from 0.04 to 0.16 % in the region between 1.6 K and a room temperature. The central peak and the observed satellites can be assigned to the metallic Cu(1) and less metallic Cu(2) in the crystalline structure of CuS. An anomalous negative Knight shift is estimated for the metallic Cu(1). The spin-lattice relaxations times, ${\mathrm{T}}_{1}$ have also been measured for both the Cu(1) and Cu(2) nuclei. ${\mathrm{T}}_{1}$ for Cu(2) nuclei is about 55 ms at 15 K, while that for Cu(1) nuclei is anisotropic and anomalously short 4 ms at 15 K, which suggests the metallic character in the plane formed by Cu(1)-S bonds.