Assessment of the magnetic entropy change of (La0.6Pr0.4)(Fe, Si)13 under cycling

Characterisation of the magnetocaloric effect via indirect determination of the magnetic entropy change ΔS, provides valuable information about the material, but may not necessarily give an assessment of the suitability of the material for an application While in laboratory tests a material undergoes only one test cycle, in a magnetic refrigerator multiple field cycles occur every second A realistic assessment may be obtained via direct measurement of the adiabatic temperature change ΔT_ad, however, dedicated devices are required and are not readily available In addition, for materials undergoing a first order phase transition, application of the Maxwell relation may lead to unphysical results due to the coexistence of phases [1-3]. We overcome these challenges by carefully choosing the measurement protocols and analysis procedures A discontinuous measurement protocol provides the response of the material after all thermal and magnetic history has been erased and the material starts from a uniform state before any transition takes place Measurements of any subsequent cycles then include unphysical results Here we present a procedure on how the cyclic behaviour of the magnetocaloric effect can be determined from indirect measurements of entropy change We select (La, Pr)(Fe, Si)₁₃ as a model material with a first order phase transition In comparison to La(Fe, Si)₁₃ the first order character of (La, Pr)(Fe, Si)₁₃ is enhanced, leading to an increase in thermal hysteresis [4]. While an increase in hysteresis is unfavourable from an application point of view, it makes the material ideal to study the cycle dependent thermomagnetic behaviour associated with the first order transition We propose a method for extracting the cyclic magnetic entropy change of a magnetocaloric material for data which was obtained by indirect characterisation methods under quasi-static non-cyclic conditions.