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

Abstract

This paper presents a review and results of comparative study of the influence of Gd on some physical properties of (R0.9R′0.1)1−xGdxCo2 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 TC of the compounds. The maximum percentage increase in TC, namely, ~43% was observed for (Ho0.9Er0.1)1−xGdxCo2. However, the highest temperature was noted for the (Dy0.9Ho0.1)0.85Gd0.15Co2 solid solution; it is TC=183.4K. 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 TC 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 ΔTad=3K and highest isothermal entropy change ΔSmag=12.1J/kgK were observed for (Ho0.9Er0.1)0.95Gd0.05Co2 at ~90K in magnetic fields of 2T and 3T, respectively. A decrease in the entropy change has been observed with increasing Gd content in all studied samples. The smallest values of ΔSmag were observed for the (Dy0.9Ho0.1)1−xGdxCo2 solid solutions. Under an external field change of from 0 to 3T, the maximum entropy change for (Dy0.9Ho0.1)1−xGdxCo2 compounds decreases from 6.9at x=0.05–4.3J/kgK 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.