Specific heat and NMR studies on the pyrite-type superconductors CuS2 and CuSe2

We have investigated the superconducting and magnetic properties of the pyrite-type CuS2 and CuSe2 synthesized under high pressures by measurements of specific heat, magnetization and NMR. The first measurements of the specific heat gave T-S = 1.50(2.47)K and Delta C/gamma T-S = 1.34(1.47) for CuS2 (CuSe2). The broad NMR spectra for Cu-63,Cu-65 in CuS2 measured at 1.3 K in various fields can be explained well by assuming the incommensurate CDW transition occurs at 150 K. The magnetization mesurements in CuS2 (type B) showed the weak ferromagnetism with T-C = 23 K. (C) 2000 Published by Elsevier Science B.V. All rights reserved.