Abstract
We have prepared polycrystalline La0.7Sr0.3Mn1−xNixO3 (x = 0, 0.01, 0.02, 0.03) samples by conventional solid-state reaction. X-ray absorption studies reveal that Ni dopants in the compounds having an oxidation state of 2+. These Ni2+ ions replace Mn on the octahedral site of the perovskite structure. An increase of the Ni content enhances the concentration of Mn4+ ions. This reduces magnetization, and the ferromagnetic-paramagnetic phase transition temperature (TC) of La0.7Sr0.3Mn1−xNixO3 from ∼365 K for x = 0 to ∼345 K for x = 0.03. The magnetocaloric effect has also been assessed by means of magnetic-entropy change, which is determined from field dependences of magnetization. We find a large magnetic-entropy change taking place around TC of the samples. Under an applied field interval of 15 kOe, the maximum magnetic-entropy changes |ΔSMmax| are about 2.33, 2.27, 2.26 and 2.21 J/kg K for x = 0, 0.01, 0.02, and 0.03, respectively. Interestingly, the doping of a small amount of Ni in La0.7Sr0.3Mn1−xNixO3 does not make|ΔSMmax| changed very much, but causes the shift of this value towards room temperature. Such the feature is applicable to control the working temperature range of cooling systems based on the magnetocaloric effect.
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