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(nv)=a(v)e(ik.R(n))+a(v)* e(-ik.R(n)) with incommensurate modulation vectors k=0.466b* and 0.418b* in the low (T < T(M)) and intermediate (T(N) < T< T(M)) temperature phases, respectively. The polarization vectors a(v) 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 mu(B) (m(rms)a=0.72, m(rms)b=0.31, m(rms)c=0.29 mu(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 mu(B) (m(rms)a=0.56, m(rms)c=0.22 mu(B)) at T=4.8 K.