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

The magnetic structure of the Fe2P-type R6CoTe2 phases (R=Gd–Er, space group P6¯2m) has been investigated through magnetization measurement and neutron powder diffraction. All phases demonstrate high-temperature ferromagnetic and low-temperature transitions: TC=220K and TCN=180K for Gd6CoTe2, TC=174K and TCN=52K for Tb6CoTe2, TC=125K and TCN=26K for Dy6CoTe2, TCN=60K and TN=22K for Ho6CoTe2 and TCN∼30K and TN∼14K for Er6CoTe2.Between 174 and 52K Tb6CoTe2 has a collinear magnetic structure with K0=[0, 0, 0] and with magnetic moments along the c-axis, whereas below 52K it adopts a non-collinear ferromagnetic one.Below 60K the magnetic structure of Ho6CoTe2 is that of a non-collinear ferromagnet. The holmium magnetic components with a K0=[0, 0, 0] wave vector are aligned ferromagneticaly along the c-axis, whereas the magnetic component with a K1=[1/2, 1/2, 0] wave vector are arranged in the ab plane. The low-temperature magnetic transition at ∼22K coincides with the reorientation of the Ho magnetic component with the K0 vector from the collinear to the non-collinear state.Below 30K Er6CoTe2 shows an amplitude-modulate magnetic structure with a collinear arrangement of magnetic components with K0=[0, 0, 0] and K1=[1/2, 1/2, 0]. The low-temperature magnetic transition at ∼14K corresponds to the variation in the magnitudes of the MErK0 and MErK1 magnetic components.In these phases, no local moment was detected on the cobalt site.The magnetic entropy of Gd6CoTe2 increases from ΔSmag=−4.5J/kgK at 220K up to ΔSmag=−6.5J/kgK at 180K for the field change Δμ0H=0–5T.