Abstract
Rare-earth (RE) rich intermetallics crystallizing in orthorhombic Ho6Co2Ga-type crystal structure exhibit peculiar magnetic properties that are not widely reported for their magnetic ordering, order of magnetic phase transition, and related magnetocaloric behavior. By tuning the type of RE element in RE6Co2Ga (RE = Ho, Dy or Gd) compounds, metamagnetic anti-to-paramagnetic (AF to PM) phase transitions could be tuned to ferro-to-paramagnetic (FM to PM) phase transitions. Furthermore, the FM ground state for Gd6Co2Ga is confirmed by density functional theory calculations in addition to experimental observations. The field dependence magnetocaloric and Banerjee’s criteria demonstrate that Ho6Co2Ga and Dy6Co2Ga undergo a first-order phase transition in addition to a second-order phase transition, whereas only the latter is observed for Gd6Co2Ga. The two extreme alloys of the series, Ho6Co2Ga and Gd6Co2Ga, show maximum isothermal entropy change (∣ΔSisomax(5 T)∣) of 10.1 and 9.1 J kg−1K−1 at 26 and 75 K, close to H2 and N2 liquefaction, respectively. This outstanding magnetocaloric effect performance makes the RE6Co2Ga series of potential for cryogenic magnetic refrigeration applications.
Highlights
The pursuit of energy conservation and environmental protection has become the mainstream of modern society
The performance of magnetocaloric effect (MCE) materials can be evaluated by the magnetic entropy change in an isothermal process (ΔSiso) and/or temperature change in an adiabatic process (ΔTad), which are correlated to thermomagnetic phase transitions of the materials
MCE materials are classified into the order of thermomagnetic phase transitions they undergo
Summary
The pursuit of energy conservation and environmental protection has become the mainstream of modern society. The vapor-compression refrigeration, a widely used technology in transportation, and residential, commercial, and industrial refrigeration, can no longer meet the current development needs due to its low efficiency, adverse environmental impact, and noise of the compressor. The use of natural gas as well as H2, He, N2, and O2, is widely extended with several scientific, industrial, and commercial purposes. Their consumption is expected to increase in future years. MCE materials are classified into the order of thermomagnetic phase transitions they undergo. For those undergoing first-order phase transition (FOPT), they usually exhibit large ΔSiso values, but their accompanying thermal and magnetic hystereses can affect their cyclicality. For those exhibiting second-order phase transition (SOPT), while they exhibit no hysteresis, their ΔSiso values may be lower than those of FOPT materials [11,12,13]
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