Single crystal neutron diffraction study of the magnetic structure of TmNi2B2C

Neutron diffraction techniques have been used to study the magnetic structure of single crystals of the magnetic superconductor (T-c congruent to 11 K) TmNi2B2C. We find that below approximately 1.5 K the magnetic moments order in an incommensurate spin wave with propagation vector q(m) = q(m)(a*+b*) [or q(m) = q(m)(a*-b*)] with q(m) = 0.094 +/- 0.001. The spin wave is transverse with the moments aligned along the c axis, and the observation of relatively intense higher-order harmonics shows that the modulation is not purely sinusoidal but considerably squared. This incommensurate magnetic structure, which coexists with superconductivity below T-N congruent to 1.5 K, is quite different from those observed in the magnetic superconductors HoNi2B2C and ErNi2B2C. The origin of diffraction peaks observed in scans parallel to a* is briefly discussed. (C) 1997 American Institute of Physics.