MUON-SPIN-ROTATION STUDIES OF HONI2B2C

Muon-spin-rotation and relaxation studies on single-crystalline HoNi2B 2C show two magnetic phase transitions at T-N1=6.0 K and at T-N2=5.0 K . While the low-temperature phase displays a commensurate antiferromag netic structure, the higher-temperature phase exhibits an incommensura tely sinusoidal modulation of the spin amplitude. The nature of the in commensurate state, along with the causes of the reentrant superconduc tivity near 5 K, are discussed.