Improvement of magnetocaloric properties of Gd-Ge-Si alloys by alloying with iron

Abstract

Abstract. The influence of annealing of Gd 5 Ge 2 Si 2 Fe x alloys at 1200°C and of alloying with various amount of iron on structure as well as thermal and magnetocaloric properties is investigated. It was found that annealing for 1 to 10 hours improves the entropy change, but reduces the temperature of maximum magnetocaloric effect by up to 50 K. Prolonged annealing of the Gd 5 Ge 2 Si 2 alloy results in the decrease of entropy change due to the reduction of Gd 5 Ge 2 Si 2 phase content. Addition of iron to the ternary alloy enhances the magnetocaloric effect, if x = 0.4 -0.6, especially if alloying is combined with annealing at 1200°C: the peak value of the isothermal entropy change from 0 to 2 T increases from 3.5 to 11 J/kgK. Simultaneously, the temperature of maximum magnetocaloric effect drops to 250 K. The changes in magnetocaloric properties are related to the change in phase transformation from the second order for arc molten ternary alloy to first order in the case of annealed and/or alloyed with iron. The results of this study indicate that the minor addition of iron and heat treatment to Gd-Ge-Si alloys may be useful in improving the materials' magnetocaloric properties..

Investigation of Critical Behavior in Gd75Ge15Si5Ce5 Alloy

“…For several years, the chemical composition of the Gd 5 Si 2 Ge 2 has been intensively modified in order to improve magnetocaloric properties. As it was shown in [2,3], the additions such as Al, Cu, Ga, Mn, Co cause an increase in the Curie temperature and imply second order phase transition, which decreases the magnetic entropy change. Hasiak in [4] has shown that small amount of Ni addition leads to decrease of the Curie temperature and slight increase of magnetic entropy change is observed.…”

Effect of Co, Ti and Cr Additions on Microstructure, Magnetic Properties and Corrosion Resistance of Magnetocaloric Gd-Ge-Si Alloys

“…These alloys are intensively investigated because they exhibit high magnetocaloric effect (MCE), represented by magnetic entropy changed (|ΔS M |), in the vicinity of the Curie point, which is close to the room temperature [ 18 , 19 , 20 ]. It was also shown that the Curie temperature could be changed by the introduction to master alloys additives such as Co, Fe, Zr, Pr, Ni or Ce [ 9 , 16 , 18 , 21 , 22 ]. High MCE in these alloys allows them to be used in cooling technology, for example, in the production of ecofriendly magnetic refrigerators [ 23 , 24 , 25 , 26 , 27 ].…”