SINGLE-CRYSTAL NEUTRON-DIFFRACTION STUDY OF THE MAGNETIC-STRUCTURE OFTMNI2B2C

Neutron diffraction techniques have been used to study the magnetic st ructure of single crystals of the magnetic superconductor (T-c congrue nt to 11 K) TmNi2B2C. We find that below approximately 1.5 K the magne tic moments order in an incommensurate spin wave with propagation vect or 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 s quared. This incommensurate magnetic structure, which coexists with su perconductivity 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 br iefly discussed. (C) 1997 American Institute of Physics.