Nature of magnetic phase transitions in TbCu 2X 2 (X = Si, Ge) and HoCu 2Si 2 compounds

Abstract

Physical properties of TbCu 2X 2 (X = Si, Ge) and HoCu 2Si 2, crystallizing with the tetragonal ThCr 2Si 2-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 TbCu 2Si 2, 13 K for TbCu 2Ge 2 and 6.4 K for HoCu 2Si 2. 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 T t = 8.5 K for TbCu 2Si 2 and 9.7 K for TbCu 2Ge 2. In HoCu 2Si 2 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 = 4.7 K.