Magnetothermal Properties and Magnetocaloric Effect in the 3d Ferromagnetic Elements: Fe, Co, and Ni

2023AbstractWe present a calculation of magnetothermal properties and magnetocaloric effect (MCE) for the ferromagnetic elements:Fe, Co, and Ni. In particular, we calculated the temperature and field dependences of magnetization, heat capacity, entropy,isothermal entropy changeΔSm, adiabatic temperature change ΔTad, and the two figures-of-merit: the relative cooling pow-ers RCP(S) and RCP(T). We have used the mean-field theory in calculating the magnetization, magnetic heat capacity, andmagnetic entropy. The lattice and electronic contributions to the total heat capacity and entropy were calculated using standardrelations to subsequently calculateΔTad. Those contributions depend on the Debye temperature ΘD and the coefficient of theelectronic heat capacity γe respectively. The Maxwell relation is used to calculateΔSm andΔTad. As an example of our results,the maximumΔSm for the three elements, in 6 T, is between 0.17 to 0.36 J/mol K and the maximumΔTad is between 0.46 to1.5 K/T for the same field change. The relative cooling power RCP(S) is in the 15–36 J/mol range for the three elements in a6 T field. Also, the relative cooling power, RCP (T), is in the 162–1044K2 range for the same field. For Fe and Co the RCP(T) per Tesla values, i.e., 139 and 174K2∕T respectively are comparable to that of Gd and other Gd-based magnetocaloricmaterials. The behavior of the magnetization, magnetic heat capacity, and magnetic entropy shows that the phase transitionin these three elements is of the second order. The universal curve and Arrott plots further support this conclusion.