Magnetic properties of Fe2P-type R6CoTe2 compounds (R=Gd–Er)

The magnetic structure of the Fe 2 P-type R 6 CoTe 2 phases ( R =Gd–Er, space group P 6¯2 m ) has been investigated through magnetization measurement and neutron powder diffraction. All phases demonstrate high-temperature ferromagnetic and low-temperature transitions: T C =220 K and T CN =180 K for Gd 6 CoTe 2 , T C =174 K and T CN =52 K for Tb 6 CoTe 2 , T C =125 K and T CN =26 K for Dy 6 CoTe 2 , T CN =60 K and T N =22 K for Ho 6 CoTe 2 and T CN ∼30 K and T N ∼14 K for Er 6 CoTe 2 . Between 174 and 52 K Tb 6 CoTe 2 has a collinear magnetic structure with K 0 =[0, 0, 0] and with magnetic moments along the c -axis, whereas below 52 K it adopts a non-collinear ferromagnetic one. Below 60 K the magnetic structure of Ho 6 CoTe 2 is that of a non-collinear ferromagnet. The holmium magnetic components with a K 0 =[0, 0, 0] wave vector are aligned ferromagneticaly along the c -axis, whereas the magnetic component with a K 1 =[1/2, 1/2, 0] wave vector are arranged in the ab plane. The low-temperature magnetic transition at ∼22 K coincides with the reorientation of the Ho magnetic component with the K 0 vector from the collinear to the non-collinear state. Below 30 K Er 6 CoTe 2 shows an amplitude-modulate magnetic structure with a collinear arrangement of magnetic components with K 0 =[0, 0, 0] and K 1 =[1/2, 1/2, 0]. The low-temperature magnetic transition at ∼14 K corresponds to the variation in the magnitudes of the M Er K0 and M Er K1 magnetic components. In these phases, no local moment was detected on the cobalt site. The magnetic entropy of Gd 6 CoTe 2 increases from Δ S mag =−4.5 J/kg K at 220 K up to Δ S mag =−6.5 J/kg K at 180 K for the field change Δ μ 0 H =0–5 T.