Structural, magnetic and magnetocaloric properties in La 0.67 (Sr 1− x Mg x ) 0.33 MnO 3 ( x = 0, 0.1, 0.3) compounds

The La 0.67 (Sr 1− x Mg x ) 0.33 MnO 3 ( x = 0, 0.1, 0.3) manganites have been prepared by sol–gel method, and the effect of Mg doping on their structure, magnetic and magnetocaloric properties has been researched. All the samples are crystallized in perovskite rhombohedral structure with space group R3c . The slight increases in the edge length a and the cell volume with Mg doping indicates the replacement of Mg in Mn-site. The corresponding change of structure parameters, such as Mn–O bond length and Mn–O–Mn bond angle, weakens the exchange coupling between Mn 3+ and Mn 4+ and results in the decrease in the Curie temperature ( T C ). With increasing content of Mg, the local inhomogeneity and Griffiths-like phase evolve and induce the deviation of critical exponents from the mean-field model. The existence of these short-range ferromagnetic clusters broadens the temperature range of magnetic transition process, then depresses the magnetic entropy change (|Δ S M |) and flattens the |Δ S M |- T curve. The La 0.67 (Sr 0.7 Mg 0.3 ) 0.33 MnO 3 possesses a table-like magnetocaloric effect near room temperature (|Δ S M | is nearly constant of 0.51 ± 0.01 J kg −1 K −1 for field change of 1 T in the temperature range of 277 302 K), which is beneficial for the Ericsson cycle magnetic refrigerator.