Entropy change at magnetic phase transitions of the first order and second order

• The magnetocaloric effect is measured by direct calorimetry.
• We take into account the thermal contact resistance.
• We study Gd, La(Fe–Mn–Si)13–H, La(Fe–Co–Si)13 and Ni–Mn–Co–Sn.
• We make a statistical thermodynamics theory including magnetism and structure.
• We compare the experimental s(H,T) with the theory.

Magnetocaloric properties close to first order and second order phase transitions are presented and discussed. The specific heat capacity as a function of the magnetic field and the magnetic field induced entropy change has been measured by direct heat flux calorimetry in Gd, hydrogenated La(Fe–Mn–Si)13, La(Fe–Co–Si)13 and the Heusler alloy Ni–Mn–Co–Sn. The resulting s(Ha,T) entropy constitutive relation is compared with a model including the ferromagnetic, electronic and structural contributions to the free energy.