| Magnetic refrigeration has attracted increasing attention due to its excellent properties, such as environmental friendliness and high energy efficiency. It is expected to replace traditional vapor-compression refrigeration in the near future. Among all of the magnetocaloric effect materilas,the rare earth-based magnetic crystalline materials have superior magnetocaloric effect(MCE), such as high magnetic entropy change(ΔSm). Because of the first order mangetic transition in crystalline materials, thermal hysteresis and magnetic hysteresis are inavoidable. Amorphous materials experience a second-order magnetic transition which will broaden magnetic entropy change peaks and result in large values of refrigeration capacity. With the background, Gd-TM-Al(TM=Ni, Fe) amorphous(Am.) and nanocrystalline(NC) materials are desighed based on the idea of combination fuction of amorphous and nanocrystalline composites. In this way, the amorphous part which will contribute to the wide temperature range of δFWHM and the nanocrystalline part which will give high magnetic entropy change. In this paper, magnetocaloric effect of Gd-TM-Al(TM=Ni, Fe) materials was systematically investigated.The magnetocaloric effect of Gdx(Ni0.58Al0.42)100-x(x=70,80,90)alloys were investigated. As the result, with the increase of Gd content, the curie temperature of amorphous and nanocrystalline part slightly increaded. It was also found that the magnetic entropy change of amorphous part decreased with increasing of Gd content, however, the maximum values of-ΔSm of nanocrystalline part increased. Double refrigeration regions were discovered in x=80 and 90 alloys. In the low temperature refrigeration region, a platform of magnetic entropy change was obtained for x=80 and 90 slloys. The temperature span of magnetic entropy change is between ~90 K and 120 K, and the plateau values are 4.7 and 3.6 J kg-1K-1, corresponding to x=80 and x=90, respectively.In order to obtain Gd-based magnetic refrigeration materials with high curie temperature(Tc) and magnetic entropy change(ΔSm), we have investigated MCE of Gdx(Fe0.566Al0.434)100-x(x=65-90)alloys in Gd-TM-Al(TM= Fe) alloy systems. It was found that monolithic amorphous structure can be observed for with compositions of x=65, 70 and 73.5. However, obvious crystalline peaks can be seen in samples with composition of x=80 and x=90, which reveals the presence of nanocrystallines. Full width at half maximum(δFWHM) of ΔSM up to 140-240 K, large ΔSM ~5-7.2 J kg-1 K-1 and high refrigeration capacity ~690-867 J kg-1 were obtained under a magnetic field change of 5 T for Gdx(Fe56.6Al43.4)100-x(x=65-90) ribbons.In order to research the impact of heat treatment on Gd-TM-Al(TM= Ni, Fe) alloy systems, two kinds of annealing were applied to Gd90Ni5.8Al4.2 amorphous/ nanocrystalline alloy and Gd70Fe17Al13 amorphous alloy. One is relaxation annealing(below glass transition temperature), and the other is crystalline annealing(beyond crystalline temperature of amorphous alloy). The structure relaxation was just hanppend in Gd70Fe17Al13 amorphous alloy by heat treatment below glass transition temperature. The curie temperature of amorphous alloy first decreased, and then increased with the increasing of crystallization annealing temperature. With the increase of crystallization annealing temperature, the Tc and ΔSM of amorphous part in Gd90Ni5.8Al4.2 amorphous/ nanocrystalline alloy decreased, and the Tc of nanocrystalline part slightly increased. The ΔSM of nanocrystalline part first decreased and then gave a stable tendency. |
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