Abstract
In this paper, the magnetocaloric properties of Gd1−xTbx alloys were studied and the optimum composition was determined to be Gd0.73Tb0.27. On the basis of Gd0.73Tb0.27, the influence of different Fe-doping content was discussed and the effect of heat treatment was also investigated. The adiabatic temperature change (ΔTad) obtained by the direct measurement method (under a low magnetic field of 1.2 T) and specific heat capacity calculation method (indirect measurement) was used to characterize the magnetocaloric properties of Gd1−xTbx(x = 0~0.4) and (Gd0.73Tb0.27)1−yFey (y = 0~0.15), and the isothermal magnetic entropy (ΔSM) was also used as a reference parameter for evaluating the magnetocaloric properties of samples together with ΔTad. In Gd1−xTbx alloys, the Curie temperature (Tc) decreased from 293 K (x = 0) to 257 K (x = 0.4) with increasing Tb content, and the Gd0.73Tb0.27 alloy obtained the best adiabatic temperature change, which was ~3.5 K in a magnetic field up to 1.2 T (Tc = 276 K). When the doping content of Fe increased from y = 0 to y = 0.15, the Tc of (Gd0.73Tb0.27)1−yFey (y = 0~0.15) alloys increased significantly from 276 K (y = 0) to 281 K (y = 0.15), and a good magnetocaloric effect was maintained. The annealing of alloys (Gd0.73Tb0.27)1−yFey (y = 0~0.15) at 1073 K for 10 h resulted in an average increase of 0.3 K in the maximum adiabatic temperature change and a slight increase in Tc. This study is of great significance for the study of magnetic refrigeration materials with adjustable Curie temperature in a low magnetic field.
Highlights
Magnetic refrigeration technology based on magnetocaloric effect (MCE) has gained wide attention because of its high efficiency and low carbon dioxide emissions
The ideal operating temperature of the magnetic refrigeration material is near the Curie temperature, because the adiabatic temperature change and the isothermal magnetic entropy reach peaks in this temperature range
By the comparing the adiabatic value oftemperature the adiabatic temperature change achieved by indirect measurement method and direct measurement method under 1.2 T magnetic field, we found that the peak value was the same, about 3.5 K, which shows that the direct measurement method and the indirect measurement method were in good agreement
Summary
Magnetic refrigeration technology based on magnetocaloric effect (MCE) has gained wide attention because of its high efficiency and low carbon dioxide emissions. The MCE is the endothermic and exothermic behaviors of materials with a change in the applied magnetic field, and it is evaluated by adiabatic temperature change (∆Tad ) and isothermal magnetic entropy (∆SM ). The adiabatic temperature change (∆Tad ) measured by direct measurement method (i.e., ∆Tad is the difference among the temperature of the sample measured directly at Hi and Hf , where Hf and Hi are the final and initial magnetic fields, respectively) and specific heat capacity calculation method (indirect measurement) is suitable for practical applications [18]. Most of the magnetic refrigeration processes are dynamic, so the ∆Tad obtained by the indirect measurement method was used as supplementary data and reference for the direct measurement method in this paper [2] These two methods can be applied in both first-order and second-order phase transition magnetic materials. After the Gd1−x Tbx alloy system was determined, the effects of doping a small amount of Fe and adding heat treatment on the MCE were revealed
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