Magnetocaloric Effect in R6Fe23: R = Dy, Ho, Er, and Tm

Abstract

We present a mean field study on the R₆Fe₂₃ system, where R = Dy, Ho, Er, and Tm, to calculate the magnetization, magnetic heat capacity, and the magnetocaloric effect (MCE) (isothermal entropy change (ΔS_m) and the adiabatic temperature change (ΔT_ad)) for different field changes up to 5 T and at temperatures ranging from 0 to 600 K. The maximum ΔS_m, using the trapezoidal method, for the R₆Fe₂₃ system is in the range 4.9–9.8 J/K mol, and the maximum ΔT_ad is in the range 9.56–15.17 K for a field change ΔH = 5 T. The largest ΔS_m and largest ΔT_ad are found for Tm₆Fe₂₃ to be 9.8 J/K mol and 15.17 K at Curie temperature T_c = 489 K, for ΔH = 5 T. The relative cooling power RCP(S) is in the range 148–560 J/mol for ΔH = 5 T, which is comparable to that of bench-mark materials, e.g., Gd. Also, the RCP based on the adiabatic temperature change, RCP(T) is in the range 449–1092 K² for ΔH = 5 T, which is comparable also to that of bench-mark materials, e.g., Gd. We investigated the type of phase transition in the light of universal curves, Arrott plots, and the behavior of the magnetic moment, magnetic heat capacity, and MCE (ΔS_m, ΔT_ad), which confirm that the type of phase transition at T_c of this system is second-order phase transition (SOPT). A calculation of some critical exponents adds more evidence that the MFT is fairly suitable to handle the aforementioned properties in the studied systems.