Influence of thermal hysteresis and field cycling on the magnetocaloric effect in LaFe11.6Si1.4

The adiabatic temperature change Delta T-ad at a field-induced first-order transition can be different when a magnetic field H is applied the first time compared to measurements under further applications of H. This can lead to overestimation of the magnetocaloric effect (MCE) if only the first field cycle is considered. In polycrystalline LaFe11.6Si1.4, for Delta mu H-0 = 1.93 T, field cycling reduces the achieved value of Delta T-ad from 7 K to about 5.8 K. A metastable entropy-temperature diagram has been constructed from experimental isofield heat capacity data, which is used to comprehensively analyze results of direct measurements of Delta T-ad(T)(0 -> H) and isothermal magnetization measurements. It is shown that the reduction in Delta T-ad by field cycling is due to the presence of two-phase states that are stabilized by thermal hysteresis. Relations between optimum operational MCE parameters of a magnetic refrigerant and the maximum available field H-avl have been obtained by the approach of an idealized first-order transition. (C) 2012 Elsevier B.V. All rights reserved.