Incommensurate modulated magnetic structure in the heavy electron compoundYbPtAl

Yb-170 Mossbauer spectroscopy measurements down to 0.025 K and neutron diff raction measurements down to 1.7 K have been performed in the heavy electro n compound YbPtAl(T-N similar or equal to 5.8 K). Below T-N the neutron dat a show that the magnetic structure is incommensurate, with a wave-vector k = (0.30. 0. 0). At 0.035 K, the Mossbauer data reveal that the magnetic str ucture is modulated and that it is not an antiphase structure. YbPtAl is a clear example of a Kramers local moment system where the Kondo singlet grou nd state allows a modulated magnetic structure to persist down to 0 K. (C) 2000 Elsevier Science B.V. All rights reserved.