A study of magnetism and magnetocaloric effect in Ho1-x Tb x Co2 compounds

Structural, magnetic phase transition and magnetocaloric properties of Ho1-x Tb x Co2 (x=0, 0.1, 0.2, 0.4, 0.6, 0.8 and 1) compounds were investigated by X-ray diffraction, Landau theory and magnetic measurements. The Ho1-x Tb x Co2 compounds present a cubic MgCu2-type structure. Lattice parameter and Curie temperature (TC) are increased, respectively, from 7.1632 to 7.2037 A and from 81 to 233 K with increasing Tb concentration (x=0-1). Isothermal entropy change ΔS was calculated according to magnetic measurements using thermodynamic Maxwell's relation. A large entropy change has been observed for low-Tb concentrations. Under an external field change from 0 to 5 T, the entropy change is about 15 J/kg K (T C=97 K), 9.4 J/kg K (T C=149 K), 6.8 J/kg K (T C=211 K) for x=0.1, 0.4 and 0.8, respectively. The associated reduction in the magnetocaloric effect of Ho1-x Tb x Co2 compounds could be explained by the fact that the increase in the Tb concentration transforms the transition from first order to second order. However, no dramatic change was observed in relative cooling power (RCP)