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• RFe 2 Si 2 (R = Ho, Tm) intermetallic compounds were successfully synthesized. • Ultra-low working temperature and large low-field magnetocaloric effect were obtained. • Good thermal and magnetic reversibility were confirmed based on the analysis of transition. • RFe 2 Si 2 (R = Ho, Tm) compounds show potential applications on low-temperature magnetic cooling. Nowadays, magnetic refrigerant technology has drawn much attention for its environmental friendliness. Those magnetic materials possessing giant low-field magnetocaloric effect (MCE) performance are of great importance for practical applications, especially at low temperatures. Herein, we present a detailed study on polycrystalline magnetocaloric compounds HoFe 2 Si 2 and TmFe 2 Si 2. HoFe 2 Si 2 exhibits a transition from antiferromagnetic to paramagnetic phase at 2.2 K, while no long-range magnetic ordering is observed in TmFe 2 Si 2 even temperature down to 2 K. For both compounds, they showed large low-field magnetic entropy change (−ΔS M) with the peak values of 10.6 and 7.9 J kg−1 K−1 under field change of 0–2 T for HoFe 2 Si 2 and TmFe 2 Si 2 , respectively, which is comparable or even larger than some low-temperature magnetocaloric materials. In addition, the characteristic of second-order magnetic transitions of both compounds were confirmed on basis of Arrott plots and mean-field theory criterion. The low magnetic ordering temperatures, large low-field MCE performance along with the feature of second order phase transition for HoFe 2 Si 2 and TmFe 2 Si 2 indicate that both compounds are promising candidate for magnetic refrigerant materials at liquid helium temperature. [ABSTRACT FROM AUTHOR]

• Large low-temperature MCE was obtained in R 3 Ni 6 Al 2 compounds. • Large refrigeration capacity in Dy 3 Ni 6 Al 2 compound was observed. • The magnetic transitions were confirmed to be second order. Large magnetocaloric effect (MCE) and magnetic properties in R 3 Ni 6 Al 2 (R = Dy, Ho and Er) compounds were systematically investigated. Large magnetic moment and low magnetic transition temperature play a decisive role in the magnetocaloric performance for R 3 Ni 6 Al 2 (R = Dy, Ho and Er) compounds. Ho 3 Ni 6 Al 2 compound shows the largest magnetic entropy change with the value of 19.7 J/kg K at ~20 K under field change of 0–5 T because of the large magnetic moment and moderate transition temperature. For Dy 3 Ni 6 Al 2 compound, it exhibits the largest refrigeration capacity with the value of 394.5 J/kg due to the successive magnetic transitions. The Er 3 Ni 6 Al 2 compound has a large MCE at ultra-low temperatures around 4 K. Furthermore, the second-order phase transition in R 3 Ni 6 Al 2 (R = Dy, Ho, Er) compounds were confirmed according to Arrott plots, rescaled universal magnetic entropy change curves and mean field theory with negligible thermal and magnetic hysteresis. The large reversible MCE with low working temperatures indicates that R 3 Ni 6 Al 2 compounds are potential excellent MCE materials for low-temperature magnetic refrigeration. [ABSTRACT FROM AUTHOR]

High-efficiency and environment-friendly magnetic refrigeration, as a replacement to conventional gas compression, has drawn increasing attention. In this article, polycrystalline TmCoSi and TmCuSi compounds were successfully synthesized and giant low field magnetocaloric effect (MCE) was investigated. Under field change of 0–1 T, (-ΔS M) max of 12.0 J/kg K and 8.7 J/kg K and (ΔT ad) max of 6.2 K and 3.7 K were obtained at low temperatures for TmCoSi and TmCuSi compounds, respectively. It could be considered as one of the best low-temperature MCE materials compared with reported ErMn 2 Si 2 compound showing (-ΔS M) max and (ΔT ad) max of 14.7 J/kg K and 2.5 K respectively. Furthermore, a low-field and reversible giant MCE around the boiling point of liquid helium with the negligible thermal and magnetic hysteresis indicates that TmCuSi and TmCoSi compounds could be potential candidates of magnetic refrigeration for liquid helium temperature region. • Giant MCE was obtained in TmCoSi and TmCuSi compounds in low temperature zone. • Giant MCE can be induced by field change as low as 0–1 T. • The nature of second order was confirmed by several methods in TmCoSi and TmCuSi compounds. [ABSTRACT FROM AUTHOR]