Nature of magnetic phase transitions in TbCu2X2 (X = Si, Ge) and HoCu2Si2 compounds

Physical properties of TbCu2X2 (X =Si, Ge) and HoCu2Si2, crystallizing with the tetragonal ThCr2Si2-type crystal structure, were investigated by means of neutron diffraction as well as by magnetic and calorimetric measurements. All compounds exhibit antiferromagnetic ordering below T-N equal to 12 K for TbCu2Si2, 13K for TbCu2Ge2 and 6.4K for HoCu2Si2. Neutron diffraction data indicate collinear antiferromagnetic structure described by the propagation vector (k) over right arrow = [(1/2), 0, (1/2)] at low temperatures. While increasing temperature the direction of the Tb magnetic moment changes from [1 1 0] to 101 0] at T-t = 8.5K for TbCu2Si2 and 9.7 K for TbCu2Ge2. In HoCu2Si2 a change of the magnetic structure from the collinear to a modulated one described by the propagation vector k = [k(x), 0, k(z)] was found at T-t = 4.7K. (C) 2010 Elsevier B.V. All rights reserved.