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. Anti ferromagnetic 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 ac cord with the previous specific heat measurement. The magnetic structu re is a single-Q type S(nv)=a(v)e(ik.R(n))+a(v) e(-ik.R(n)) with inco mmensurate 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 sca ttering intensities, and thus those which reproduce the intensities ar e selected using a maximum entropy method. In the low-temperature phas e, the polarization vectors have a, b and c components, and the root m ean 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-temperat ure 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.