Magnetocaloric effect: Overcoming the magnetic limit

Abstract We have studied anomalous peaks observed in magnetocaloric −Δ S ( T ) curves for systems that undergo first-order magnetostructural transitions. The origin of those peaks, which can exceed the conventional magnetic limit, R ln(2 J +1), is discussed on thermodynamic bases by introducing an additional-exchange contribution (due to exchange constant variation arising from magnetostructural transition). We also applied a semiphenomenological model to include this additional-exchange contribution in Gd 5 Si 2 Ge 2 - and MnAs-based systems, obtaining excellent results for the observed magnetocaloric effect.