B-11 pulsed nuclear magnetic resonance study of DyNi2B2C single crystals

摘要

DyNi2B2C is the only compound in the RNi2B2C (R = rare-earth element) series where superconductivity at T-c -6.2 K coexists with the antiferromagnetic ordering below the Neel temperature T-N -10.3 K. This system is of great interest because superconductivity rarely coexists with magnetic ordering. B-11 pulsed nuclear magnetic resonance (NMR) measurements were performed at 8.0056 T to investigate the local electronic structures and 4f spin dynamics of DyNi2B2C powders and single crystals. The spectrum for the single crystal showed three narrow resonance peaks at 295 K due to the nuclear Zeeman splitting of a nuclear spin I = 3/2 with quadrupolar perturbation. The B-11 NMR Knight shift of the single crystal was very large and highly anisotropic at K = -0.60% and +0.27% for the fields parallel and perpendicular, respectively, to the c-axis at 295 K. Considering the anisotropy of the Knight shift, we were able to simulate the B-11 NMR power pattern that agreed well with the measured spectrum. The linewidth for DyNi2B2C was also large and anisotropic, and the linewidth value increased rapidly at low temperatures. The B-11 NMR shift and linewidth were found to be proportional to the magnetic susceptibility, indicating that the hyperfine field at the B site originates from the 4f spins of Dy. Above T-N, the values for 1/T-1 (the spin-lattice relaxation rate) and 1/T-2 (the spin-spin relaxation rate) were very large, showing slight increases at low temperatures. Below T-N, the values of 1/T-1 and 1/T-2 were suppressed significantly because of the slowing of the 4f spin fluctuation. This confirmed the huge change in Dy 4f spin dynamics across the antiferromagnetic transition. (C) 2016 Elsevier B.V. All rights reserved.