Structural, magnetic and magnetocaloric properties in La0.67(Sr1-xMgx)0.33MnO3 (x=0, 0.1, 0.3) compounds

The La-0.67(Sr1-xMgx)(0.33)MnO3 (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 R (3) over barc. 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 Mn3+ and Mn4+ 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 (vertical bar Delta S-M vertical bar) and flattens the vertical bar Delta S-M vertical bar-T curve. The La-0.67(Sr1-xMgx)(0.33)MnO3 possesses a table-like magnetocaloric effect near room temperature (vertical bar Delta S-M vertical bar 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 similar to 302 K), which is beneficial for the Ericsson cycle magnetic refrigerator.