Entropy change and entropy production in BaFe12O19 barium ferrite

In this paper we discuss measurements of the heat exchanged along the hysteresis loop and the return branches of barium ferrite of composition BaFe12O19. The measurements show the joint presence of a dissipated heat, connected with the hysteresis losses, and an entropy change, connected with the ordering effect of the magnetic field on the system of magnetic spins. We demonstrate that when we try to separate the two contributions we have to conclude that the entropy cannot be a single-valued function of the magnetic field.