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 TN equal to 12 K for TbCu2Si2, 13 K for TbCu2Ge2 and 6.4 K for HoCu2Si2. Neutron diffraction data indicate collinear antiferromagnetic structure described by the propagation vector k→=[(1/2),0,(1/2)] at low temperatures. While increasing temperature the direction of the Tb magnetic moment changes from [1 1 0] to [0 1 0] at Tt = 8.5 K 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→=[kx,0,kz] was found at Tt = 4.7 K.

Research highlights▶ In TbCu2X2 (X = Si, Ge) and HoCu2Si2 temperature induces a change of their magnetic structures. ▶ In TbCu2X2 (X = Si, Ge) a reorientation of magnetic moments takes place. ▶ The magnetic structure of HoCu2Si2 undergoes a change from a collinear one to a modulated one at the transition temperature.