CeNi_3-type rare earth compounds: crystal structure of R_3Co_7Al_2 (R=Y, Gd-Tm) and magnetic properties of {Gd-Er}_3Co_7Al_2, {Tb, Dy}_3Ni_8Si and Dy_3Co_(7.68)Si_(1.32)

摘要

The crystal structure of new CeNi_3-type {Y, Gd-Tm}_3Co_7Al_2 (P63/mmc. N 194, hP24) compounds has been established using powder X-ray diffraction studies. The magnetism of Tb_3Ni_8Si and Dy_3Ni_8Si is dominated by rare earth sublattice and the magnetic properties of R_3Co_7Al_2 (R =Gd-Er) and Dy_3Co_(7.68)Si_(1.32) are determined by both rare earth and cobalt sublattices. Magnetization data indicate ferromagnetic ordering of {Tb, Dy}_3Ni_8Si at 32 K and 21 K, respectively. Gd_3Co_7Al_2 and Tb_3Co_7Al_2 exhibit ferromagnetic ordering at 309 K and 209 K, respectively, whereas Dy_3Co_7Al_2, Ho_3Co_7Al_2, Er_3Co_7Al_2 and Dy_3Co_(7.68)Si_(1.32) show a field dependent ferromagnetic-like ordering at 166 K, 124 K, 84 K and 226 K, respectively followed by a low temperature transition at 34 K for Dy_3Co_7Al_2, 18 K for Ho_3Co_7Al_2, 56 K for Er_3Co_7Al_2, 155 K and 42 K for Dy_3Co_(7.68)Si_(1.32). Among these compounds, Dy_3Ni_8Si shows largest magnetocaloric effect (isothermal magnetic entropy change) of −11.6 J/kg·K at 18 K in field change of 50 kOe, whereas Tb_3Co_7Al_2, Dy_3Co_7Al_2 and Dy_3Co_(7.68)Si_(1.32) exhibit best permanent magnet properties in the temperature range of 2-5 K with remanent magnetization of 11.95 μ_B/fu, 12.86 μ_B/fu and 14.4 μ_B/fu, respectively and coercive field of 3.0 kOe, 1.9 kOe and 4.4 kOe, respectively.