Magnetism and magnetocaloric effect in multicomponent Laves-phase compounds: Study and comparative analysis

This paper presents a review and results of comparative study of the influence of Gd on some physical properties of (R0.9R0.1')(1-x)GdxCo2 solid solutions with R=Dy, Ho and R'=Er, Ho and x varied from 0.05 to 0.15. Powder X-ray diffraction analysis performed at room temperature revealed that all studied solid solutions solidify with the formation of a Laves-phase MgCu2-type structure (space group Fd - 3m). The magnetization behavior and the magnetic transition are analyzed in terms of the Landau theory. The studies of magnetic properties and heat capacity showed that a relatively small Gd addition significantly increases T-C of the compounds. The maximum percentage increase in T-C, namely, similar to 43% was observed for (Ho0.9Er0.1)(1-x)GdxCo2. However, the highest temperature was noted for the (Dy0.9Ho0.1)(0.85) Gd0.15Co2 solid solution; it is T-C=183.4 K. Below the ordering temperature, all samples are ferrimagnetically ordered; at high temperatures, they are Curie-Weiss paramagnets. Moreover, a small Gd addition eliminates the field-induced magnetic transition near T-C and, as consequence, transforms the nature of magnetic transition from the first- to second-order. The magnetocaloric effect has been estimated in terms of both isothermal magnetic entropy and adiabatic temperature changes. The highest adiabatic temperature change Delta T-ad=3 K and highest isothermal entropy change Delta S-mag=12.1 J/kg K were observed for (Ho0.9Er0.1)(0.95)Gd0.05Co2 at similar to 90 K in magnetic fields of 2 T and 3 T, respectively. A decrease in the entropy change has been observed with increasing Gd content in all studied samples. The smallest values of Delta S-mag were observed for the (Dy0.9Ho0.1)(1-x)GdCo2 solid solutions. Under an external field change of from 0 to 3 T, the maximum entropy change for (Dy0.9Ho0.1)(1-x)GdxCo2 compounds decreases from 6.9 at x=0.05-4.3 J/kg K at x=0.15. The refrigerant capacity for all solid solutions (with 0.05 <= x <= 0.15) is reported. The effect of increasing Gd content in the solid solutions on their magnetic and magnetocaloric properties is discussed. (C) 2013 Elsevier Inc. All rights reserved.