The influence of substitution of Mn by Fe and Co on magnetocaloric effect and magnetoresistance properties of SmMn2Ge2

► Magnetic entropy changes of these compounds are estimated from the Maxwell equation, Maxwell Clausius Clapeyron equation, Landau theory and mean-field theory. ► Our results exhibit that the Maxwell Clausius Clapeyron equation should be used for compounds that have a first-order phase transition instead of using the Maxwell equation. ► As a result, in the antiferromagnetic state, the resistance is higher than that in the ferromagnetic state, suggesting that the MR in compounds from the RMn2X2 family may arise on the basis of a spin-valve mechanism.