Crystallographic and magnetic structure of TbSi1.67 and TbSi1.67- δ

Abstract

Results of a structure determination based on X-ray diffraction and neutron diffraction are reported for two Si defect structures of the composition TbSi 2- x with x = 0.33 - δ and 0.33, respectively. The crystal structure of TbSi 1.67 is orthorhombic (space group Imma) and derives from the δ-GdSi 2-type when 1 3 of the Si(2) site 4e at z = 0.9638 remains unoccupied. The lattice constants are a = 4.058 Å, b = 3.971 Å and c = 13.396 Å. The compound TbSi 1.67-δ has a hexagonal crystal structure (space group P6/mmm) that derives from a defect AIB 2-type structure. The lattice constants for TbSi 1.67-δ are a = 3.842 Å and c = 4.140 Å. Results of magnetic measurements and neutron diffraction are reported which show that TbSi 1.67 and TbSi 1.67-δ order antiferromagnetically below T N = 16 K and T N = 39 K, respectively. The magnetic structure of TbSi 1.67-δ is a collinear antiferromagnetic arrangement of the Tb moments with a doubling of the chemical unit cell ( k = [ 001 2 ]). The Tb moments are oriented perpendicular to the c direction. The compound TbSi 1.67 has a complex magnetic structure.