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

The adiabatic temperature change ΔTad 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 Δμ0H = 1.93 T, field cycling reduces the achieved value of ΔTad 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 ΔTad(T)0→H and isothermal magnetization measurements. It is shown that the reduction in ΔTad 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 Havl have been obtained by the approach of an idealized first-order transition.

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► Due to hysteresis the magnetocaloric effect can be overestimated if only the first field cycle is considered.
► In LaFe11.6Si1.4 field cycling reduces ΔTad form 7 to 5.8 K.
► A metastable S–T diagram has been successfully used to explain the reduction of ΔTad.
► Optimum operational parameters of a magnetic refrigerant have been obtained.