Magnetocaloric functional properties of Sm0.6Sr0.4MnO3 manganite due to advanced nanostructured morphology

The magnetocaloric effect (MCE) is the key concept to produce new, advanced, freon-like free, low cost and environmental friendly magnetic refrigerators. Among several potential materials, Sm0.6Sr0.4MnO3 manganite presents one of the highest MCE value in comparison to all other known manganites; however, its studied was only concentrated on the bulk material. To overcame this lack of the information nanoparticles and nanotubes of that highlighted manganite were successfully produced by using a sol-gel modified method. High resolution transmission electron microscopy revealed nanoparticle and nanotube diameters of 45 nm and 200 nm, respectively; and, in addition, this technique also showed that the wall of the nanotube is formed by the nanoparticles with 25 nm of diameter. The magnetocaloric potentials, ΔSM versus T curves, of the nanostructures were obtained and they are broader than the their bulk counterpart. This increases the useful temperature range of a magnetic refrigerator. But also an undesired M-shape profile for the nanotube sample was observed, due to the rising of a superparamagnetic behavior. These results also evidenced the existence of a nanoparticle size threshold below which the advantage to make the transition wider is no longer valid.