MAGNETIC-ORDERING OF TBCOSN AND HOCOSN STUDIED BY NEUTRON-DIFFRACTIONAND MAGNETIC MEASUREMENTS

The results of the neutron and X-ray diffraction and magnetometric mea surements of TbCoSn and HoCoSn compounds are reported. Both compounds crystallize in an orthorhombic TiNiSi-type structure with the space gr oup Pnma. The magnetometric measurements indicate the Neel temperature s at T-N=20.5 K for TbCoSn and T-N=8 K for HoCoSn. For TbCoSn below T- N two additional phase transitions at T-t=5.4 K and 11.6 K whereas for HoCoSn one at T-t=4 K are detected. Neutron diffraction data for both compounds indicate a modulated noncolinear structure. For TbCoSn in t he temperature range 1.4-5 K the magnetic structure is described by th e wavevector k(1)=(0,1/4,1/12). With the increase of the temperature t he change of the wavevector is observed at T-t approximate to 5 K it i s equal k(2)=(0,approximate to 1/4,0). For HoCoSn in low temperatures the wavevector is k(1)=(0,1/3,0), whereas below T-t=4 K it is k(2)=(0, 0.335,0).