MAGNETIC ORDER IN HONIBC AND ERNIBC

Neutron diffraction measurements have been performed to study the natu re of magnetic ordering in the compounds HoNiBC and ErNiBC. HoNiBC exh ibits antiferromagnetic ordering of the Ho moments with a simple comme nsurate magnetic structure below T-N = 10 K. The magnetic unit cell, d oubled along the c-direction with respect to the chemical unit cell, c onsists of ferromagnetic planes antiferromagnetically coupled along th e c-axis. On the other hand, the Er moments in ErNiBC show ferromagnet ic ordering with a Curie temperature of 4.5 K. In contrast to the case for the structurally related superconducting counterparts (HoNi2B2C a nd ErNi2B2C) no modulated magnetic structures were observed for any te mperatures above 1.4 K.