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 (ΔSm) and the adiabatic temperature change (ΔTad)) for different field changes up to 5 T and at temperatures ranging from 0 to 600 K. The maximum ΔSm, using the trapezoidal method, for the R6Fe23 system is in the range 4.9–9.8 J/K mol, and the maximum ΔTad is in the range 9.56–15.17 K for a field change ΔH = 5 T. The largest ΔSm and largest ΔTad are found for Tm6Fe23 to be 9.8 J/K mol and 15.17 K at Curie temperature Tc = 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 (ΔSm, ΔTad), which confirm that the type of phase transition at Tc 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.

We present a study on the magnetic properties and magnetocaloric effect (MCE) in R3Co11B4, where R = Pr, Nd, Tb, Dy, and Ho. The two-sublattice model is used for calculating magnetization, magnetic heat capacity, isothermal entropy change ∆Sm, and adiabatic temperature change ∆Tad, for different magnetic field changes ∆H = 1.5, 3, and 5 T and at temperatures up to 600 K. Direct and inverse MCE are shown to take place in the ferrimagnetic compounds with R = Tb, Dy, and Ho. The maximum isothermal magnetic entropy change and maximum adiabatic temperature change have been calculated for ferromagnetic Nd3Co11B4 compound to be 1.85 J/K mol and 6.5 K at Tc = 432 K, for a field change ∆H = 5 T. The relative cooling power (RCP) is in the 44–161 J/mol range for the same field change. Also, the type of phase transition is investigated in the light of Arrott plots, universal curves, and the features of the temperature and field dependences of the magnetization, heat capacity, entropy, and the magnetocaloric properties. Those features confirm that the transition at the Curie temperature of these compounds is of the second order.

We present a mean-field study on the magnetocaloric effect (MCE) in RFe10X2, where X=Mo, V, and R=Gd, Tb, Ho, Tm, Dy, Er, Nd for X=V. For X=Mo, R=Dy, Gd, and Nd. The two-sublattice model, involving the 4f (rare earth) and 3d(Fe) sublattices, is used. For both systems, magnetization, magnetic heat capacity, magnetic entropy and isothermal entropy change ∆Sm are calculated for different magnetic fields in the 0-5T range and the temperature range from 0 to 700K. Direct and inverse MCEs are shown to take place in these ferromagnetic/ferrimagnetic compounds. For a field change ∆H=5T, the maximum isothermal magnetic entropy change has been calculated for ferromagnetic NdFe10Mo2 compound to be 6.6 J/K mol at Tc=441 K. Both direct, and inverse MCEs have been found in ferrimagnetic compounds, e.g., for TmFe10V2, with maximum -∆Sm= J/K mol at Tc=521K and ∆Sm=  J/K mol at TN=127 K. Mean-field analysis is suitable for handling the systems we report on. Further study on the lattice and electronic contribution to entropy is planned.