Nature of the spin state in TmNi2B2C

We had observed earlier that in the quaternary borocarbide magnetic superco nductor TmNi2B2C (T-c = 11K, T-N = 1.5 K) quasistatic magnetic correlations persist well above TN (up to similar to 20 K), which is rather unusual. To further probe the nature of its spin state, we used magnetically oriented powder samples of TmNi2B2C and the mu-SR technique. We observe that the qua sistatic internal held has a well defined direction. The spontaneous muon p recession signal has three times the amplitude when the c-axis alignment is perpendicular to the initial muon beam polarization than when parallel. Th e transverse configuration enhances the oscillatory signal. This has enable d 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 cro ssing resonance arising from quadrupole levels of the boron nuclei. (C) 199 9 Published by Elsevier Science B.V. All rights reserved.