A concise approach for building the s - T diagram for Mn-Fe-P-Si hysteretic magnetocaloric material

The use of first order magnetocaloric materials (FOM's) in magnetic cycles is of interest for the development of efficient magnetic heat pumps. FOM's present promising magnetocaloric properties; however, hysteresis reduces the reversible adiabatic temperature change (Delta T-ad) of these materials, and consequently, impacts performance. The present paper evaluates the reversible Delta T-ad in a FOM. Six samples of the Mn-Fe-P-Si material with different transition temperatures are examined. The samples are measured for heat capacity, magnetization, and adiabatic temperature change using heating and cooling protocols to characterize hysteresis. After correcting demagnetizing fields, the entropy-temperature (s -T) diagrams are constructed and used to calculate adiabatic temperature change using four different thermal paths. The post-calculated Delta T-ad is compared with experimental data from direct Delta T-ad measurements. Most of the samples of Mn-Fe-P-Si show that post-calculated Delta T-ad resulting from the heating zero field and cooling in-field entropy curves align best with the Delta T-ad measurements. The impact of the demagnetizing field is shown in terms of absolute variation to the post-calculated Delta T-ad. A functional representation is used to explain observed data sensitivities in the post-calculated Delta T-ad.