Improvement of Magnetocaloric Effects and Study of Magneto-Transport Behavior of Lanthanum Strontium Manganites by Grain Boundary Management via Additives

The structural, transport and magnetic properties of La 0.67 Sr 0.33 MnO 3 with additives of ZrO 2 and Bi 2 O 3 were investigated and the results are presented. The studied samples showed a ferromagnetic-to-paramagnetic phase transition around 383 K, and a sharp transition was observed for the La 0.67 Sr 0.33 MnO 3 /Bi 2 O 3 sample. A soft ferromagnetic behavior at room temperature was observed in all the La 0.67 Sr 0.33 MnO 3 samples: however, the sample with bismuth oxide additive exhibited higher saturation magnetization and an enhanced magnetocaloric effect. In addition to a metal–insulator transition, a broad peak was observed in the ferromagnetic metallic region due to inhomogeneities arising from the antiferromagnetic interactions in the samples, and this disappeared with the application of a magnetic field. Positive magnetoresistance was observed for ZrO 2 added to La 0.67 Sr 0.33 MnO 3 for temperatures greater than 200 K.