COMPETITION BETWEEN MAGNETISM AND SUPERCONDUCTIVITY IN TMNI2B2C OBSERVED BY MUON-SPIN ROTATION

We report muon-spin-rotation measurements of the internal field in the rare-earth nickel boride carbide superconductor TmNi2B2C from 100 mK up to well above the superconducting transition temperature (T-c=9.5 K). An oscillatory muon response indicates that the muon is affected by a quasistatic local field that follows a T-1 dependence over a wide temperature range and without interruption at the superconducting transition. The corresponding relaxation rate remains constant in the normal state, but begins to rise very sharply with decreasing temperature below T-c scaling approximately with the local field down to its maximum at 2.5 K. The quasistatic internal field may be attributed to a spiral structure or dow three-dimensional correlations of the Tm moments. Decoupling experiments reveal a dynamic depolarization mechanism which may tentatively be ascribed to fast two-dimensional correlations of the Ni moments, slowed by the onset of superconductivity.