Magnetic and magnetocaloric properties of a foam composite based on substituted La-manganite in a polyurethane matrix

•Enhancement of the relative cooling capacity in a porous composite.•Magnetocaloric properties of a polyurethane-manganite composite.•Magnetic properties of manganite embedded into a polyurethane foam.•Increment of the magnetic entropy change by effect of a porous structure. This work deals with the effect that a porous structure causes on the magnetocaloric properties of substituted lanthanum manganite with the formula La0.67Ca0.28Sr0.05MnO3. A composite with a foam structure was fabricated using a polyurethane matrix and embedded manganite particles at three different amounts. The magnetocaloric effect was determined indirectly by mathematical adjustment of the experimental magnetization curves as a function of temperature, according to the phenomenological model proposed by Hamad. Based on the phenomenological parameters, the magnetic entropy change, ΔSm (H, T), was calculated at 1.5 T and 3.0 T. Also, the Curie temperature, the relative cooling power, RCP, the heat capacity, ΔCp, and the order of the ferromagnetic-paramagnetic transition of all the samples were determined. Results show a highlighting increase of the relative cooling power when the manganite particles are dispersed in the polymeric matrix. In addition, the magnetocaloric properties turned out to be a function of the amount of manganite embedded in the matrix. Better results were obtained at a lower manganite content. In all the studied cases, the magnetocaloric properties of the foam composite are better than that of the powder. This behavior is attributable to a change in the interaction state of the manganite particles due to the confinement that they undergo in the polymeric matrix.