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 (Tc=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 Tc 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 slow 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. © 1995 The American Physical Society