The magnetic ordering in the Ho5Si3 and Ho5Ge3 compounds

A neutron diffraction investigation has been performed on the Ho5Si3 and Ho5Ge3 compounds (hexagonal Mn5Si3-type, hP16, P6(3)/mcm) to study their magnetic structure. The results prove that these intermetallic phases show a complex sine-modulated type magnetic ordering, both presenting on cooling two subsequent antiferromagnetic (T-N1 and T-N2). Between T-N1 = 24(2) and T-N2 = 16(4) K Ho5Si3 shows a first antiferromagnetic ordering of the sine-modulated type with a propagation vector K-1 = [0,0+/-0.284(1)]: then, below T-N2 the sine-modulated type ordering is conserved. but by the two propagation vectors K-1 = [0,0+/-0.2773(7)] and K-2=[+/-1/5,+/-1/5,0]. For Ho5Ge3, between T-N1 = 27(2) and T-N2 = 18(4) K, the sine-modulated ordering is realized through the propagation vectors K-1 = [0,0+/-3/10] and K-2=[0, 1/2, 0], whilst below T-N2 the ordering takes place with propagation vectors K-1 = [0,0+/-3/10], K-2=[0, 0 +/- 2/5] and K-4 = [+/-1/5, +/-1/5, 0]. For both Ho5Si3 and Ho5Ge3 compounds, the dimensions of the magnetic unit cell are 5a x 5a x 10c times the crystal unit cell of Mn5Si3-type. (C) 2007 Elsevier B.V. All rights reserved.