Nature of the spin state in TmNi 2B 2C

Abstract

We had observed earlier that in the quaternary borocarbide magnetic superconductor TmNi 2B 2C ( T c =11 K , T N =1.5 K ) quasistatic magnetic correlations persist well above T N (up to ∼20 K), which is rather unusual. To further probe the nature of its spin state, we used magnetically oriented powder samples of TmNi 2B 2C and the μ-SR technique. We observe that the quasistatic internal field has a well defined direction. The spontaneous muon precession signal has three times the amplitude when the c-axis alignment is perpendicular to the initial muon beam polarization than when parallel. The transverse configuration enhances the oscillatory signal. This has enabled us to show that the quasistatic magnetic correlations persist even up to 50 K. Furthermore, we find a peak around 7 G in the field dependence of the longitudinal relaxation, which we attribute to the presence of a level crossing resonance arising from quadrupole levels of the boron nuclei.