Abstract
To investigate the effect of crystallization treatment on the structure and magnetocaloric effect of Gd60Co40 amorphous alloy, the melt-spun ribbons were annealed at 513 K isothermally for 20, 40 and 60 min. The results indicate that, with increasing annealing time, the Gd4Co3 (space group P63/m) and Gd12Co7 (space group P21/c) phases precipitated from the amorphous precursor in sequence. In particular, in the samples annealed for 40 and 60 min, three successive magnetic transitions corresponding to the phases of Gd4Co3, Gd12Co7 and remaining amorphous matrix were detected, which induced an overlapped broadened profile of magnetic entropy change (|ΔSM|) versus temperature. Under magnetic field changing from 0 to 5 T, |ΔSM| values of 6.65 ± 0.1 kg−1·K−1 and 6.44 ± 0.1 J kg−1·K−1 in the temperature spans of 180–196 K and 177–196 K were obtained in ribbons annealed for 40 and 60 min, respectively. Compared with the fully amorphous alloy, the enhanced relative cooling power and flattened magnetocaloric effect of partially crystallized composites making them more suitable for the Ericsson thermodynamic cycle.
Highlights
IntroductionThe total entropy S of a magnetic material is composed of magnetic entropy SM , lattice entropy SL and electronic entropy SE , among which the SM depends on both temperature and applied magnetic field strongly, while the SL and SE usually can be considered temperature dependent only [3]
Gd60 Co40 amorphous alloy (713.8 J·kg ) [17], the results reveal that the RCP increases increases with elongation of the annealing time
177–196 K observed in samples annealed at 513 K for 40 min and 60 min, enable them to be more suitable for the Ericsson thermodynamic cycle [1]
Summary
The total entropy S of a magnetic material is composed of magnetic entropy SM , lattice entropy SL and electronic entropy SE , among which the SM depends on both temperature and applied magnetic field strongly, while the SL and SE usually can be considered temperature dependent only [3]. When a ferromagnetic substance is magnetized isothermally, the alignment of magnetic moment causes enhanced magnetic order and lower SM , and the system releases heat to the surrounding environment since both SL and SE remain constant. If the magnetizing process is adiabatic, to maintain the total entropy unchanged, the SL and SE increase and the temperature becomes higher [4]. The isothermal magnetic entropy change ∆SM and adiabatic temperature change ∆Tad are important parameters to characterize the MCE of magnetic refrigerants [4]
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