In this work, we used the mean-field theory (MFT) to estimate the spontaneous magnetization Mspont(T) from the dependence of magnetic entropy change on magnetization, - Δ S M vs. M2 in Gd3Ni2 and Gd3CoNi systems. The obtained Mspont(T) values are in good agreement with those found from the classical extrapolation from the Arrott plots (H/M vs. M2), confirming that the MFT is a valid approach to estimate the spontaneous magnetization. An excellent agreement has been found between the - Δ S M values estimated by Landau theory and those obtained using the classical Maxwell relation. [ABSTRACT FROM AUTHOR]