New Er-based materials for active magnetic refrigeration below 20K

High magnetic field (0 to 9.85 T) low temperature (1.2 to 30 K) heat capacity of five as-cast alloys: Er3AlC, Er3AlC0.5, Er3AlC0.25, Er3AlC0.1 and ErAgGa revealed that four of them can be used as efficient active magnetic regenerators for magnetic refrigerators at low temperature. Only one of the carbide phases (Er3AlC) is a single phase material, while the remaining three alloys are found to be two-phase equilibrium mixtures of Er3AlC and Er2Al. Er3AlC probably orders antiferromagnetically, and ErAgGa forms a low temperature (∼3 to ∼5 K) non-magnetic atom disorder (NMAD) spin glass system. All alloys (except Er3AlC0.1) show a sufficiently high magnetocaloric effect in a range 4 to 20 K with a maximum adiabatic temperature rise of ∼12.5 K at ∼5 K for Er3AlC for magnetic field change from 0 to 7.5 T. In the carbides series, the maximum adiabatic temperature change gradually decreases from ∼12.5 K to ∼6 K and the magnetocaloric peak temperature increases from ∼5 K to ∼9 K with decreasing carbon content. The adiabatic temperature rise for the ErAgGa is ∼10% higher and covers a wider range of useful temperatures than that of the ∼50:50 mixture of Er3AlC and Er2Al (Er3AlC0.5)