Neutron Diffraction Study of Antiferromagnetic Order in the Kondo Compound CePtSn

Successive phase transitions in the Kondo compound CePtSn are studied by neutron scattering experiments on a single-crystalline sample. Antiferromagnetic phase transitions are observed at T N =6.2 K and T M =3.8 K, which are second and first order transitions, respectively, in accord with the previous specific heat measurement. The magnetic structure is a single- Q type S n ν = a ν e i k · R n + a ν * e - i k · R n with incommensurate modulation vectors k =0.466 b * and 0.418 b * in the low ( T < T M ) and intermediate ( T N < T < T M ) temperature phases, respectively. The polarization vectors a ν cannot uniquely be determined from scattering intensities, and thus those which reproduce the intensities are selected using a maximum entropy method. In the low-temperature phase, the polarization vectors have a , b and c components, and the root mean square of the moment is m rms =0.84± 0.08 µ B ( m a rms =0.72, m b rms =0.31, m c rms =0.29 µ B ) at T =2 K. In the intermediate-temperature phase, the polarization vectors have a and c components, and m rms =0.60±0.06 µ B ( m a rms =0.56, m c rms =0.22 µ B ) at T =4.8 K.