Magnetic properties of Fe 2P-type R6CoTe 2 compounds ( R=Gd–Er)

Abstract

The magnetic structure of the Fe 2P-type R 6CoTe 2 phases ( R=Gd–Er, space group P6¯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 6CoTe 2, T C=174 K and T CN=52 K for Tb 6CoTe 2, T C=125 K and T CN=26 K for Dy 6CoTe 2, T CN=60 K and T N=22 K for Ho 6CoTe 2 and T CN∼30 K and T N∼14 K for Er 6CoTe 2. Between 174 and 52 K Tb 6CoTe 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 6CoTe 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 6CoTe 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 6CoTe 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.