Reversible and irreversible magnetocaloric effect: The cases of rare-earth intermetallics YbPt_2Sn and Ce_(0.5)La_(0.5)B_6

摘要

Magnetocaloric effect (MCE) has drawn much attention because its magnetic cooling property enables refrigeration without producing noxious gas or using rapidly depleting resources. However, applications for everyday life are yet distant. In addition, we need to understand more about the practical aspect of the MCE. Here, we introduce a phenomenological model to explain the quasi-adiabatic MCE. Correction factors to the equilibrium thermodynamic feature implied by the entropy landscape are devised in analytic forms. To demonstrate the validity of the model, the MCE from two different materials is investigated. The recently discovered metallic paramagnet, YbPt2Sn, shows a linear and reversible MCE which is typical of a paramagnetic system and suitable for cryogenics without 3 He. On the other hand, a complex-phase material, Ce0.5La0.5B6, exhibits a pronounced irreversible MCE especially across a magnetic phase boundary. A term that describes the field induced heating near a phase transition turns out to be essential in resolving the irreversible, non-equilibrium MCE.