Large magnetocaloric effect near to room temperature in Sr doped La_0.7Ca_0.3MnO₃

The goal of this work is to demonstrate the positive effect of high energy ball milling on the magnetocaloric properties of materials based on strontium-calcium doped lanthanum manganite. We report a detailed study of crystal structure, magnetic behavior and magnetocaloric effect of La_0.7Ca_0.3−xSr_xMnO₃ (0 ≤ x ≤ 0.2, Δx = 0.05) powders, synthesized by assisted high-energy ball milling. The X-ray diffraction patterns disclose the complete formation of manganite with an orthorhombic structure for x ≤ 0.15, and rhombohedral structure for x = 0.2. Magnetic properties show a reduction of the magnetic saturation, and an increase in the Curie temperature with the strontium substitution, in all explored compositions (above room temperature). Arrot curves display that strontium doped manganites exhibit a second-order magnetic transition from ferrimagnetic to paramagnetic order. The magnetocaloric effect was calculated by measuring the isothermal magnetization around the Curie temperature, from 0 to 1.8 T, using Maxwell relations. All the synthesized manganites show magnetocaloric effect larger as compared to that of the parent compounds synthesized by other methods. The un-doped sample (x = 0) presents 7.43 J kg⁻¹ K⁻¹ and 93.29 J kg⁻¹ of maximum magnetic entropy change (|ΔS_M|) and the relative cooling power (RCP), respectively, under a low applied field (μ_oH) of 1.8 T. As it is expected, the introduction of strontium into the manganite, slightly reduces the magnetic entropy at 1.8 T, from 6.29 to 3.47 J kg⁻¹ K⁻¹ for x = 0.05 and x = 0.2, respectively. At the same time, the presence of strontium increases the working temperature above room temperature for strontium contents higer than 0.05, both attributed to the change in the crystal structure. These values are suitable for room-temperature magnetic refrigeration applications, using low magnetic fields (<1.8 T), increasing its potential application in the domestic refrigeration.