Abstract
In this work, we report a detailed experimental study regarding the impact of copper oxide (CuO) secondary phase and heat treatments on the structural, magnetic, and magnetocaloric properties of the near-room temperature Pr2∕3Sr1∕3MnO3 (PSMO) magnetic refrigerant. Our investigations are carried out by using structural and microstructural analyses, alongside magnetization measurements. The analysis of X-ray diffraction data of PSMO(95 %)-CuO(5 %) (PSMO-CuO) samples shows the coexistence of both CuO and PSMO phases. Further, the microstructural analysis of PSMO-CuO reveals that the addition of CuO significantly enhances the grains size. On the other hand, the added secondary phase markedly reduces the Curie temperature (Tc) from 293 K for PSMO to about 273 K for PSMO-CuO composite while increasing the magnetocaloric effect. This decrease in Tc is associated with a significant change from 162° to about 156° in the Mn-OII-Mn bond angle respectively. Moreover, performed investigations regarding the role of heat treatments unveil that the observed changes in the structural and magnetic features are mainly driven by the secondary phase that modify grains size and double-exchange interactions in the PSMO compound. Interestingly, our findings demonstrate that the Curie temperature of the PSMO and accordingly its magnetocaloric effect can be tailored by adding small amounts of CuO without need to substitution on cation sites. In the light of obtained results, a multilayered refrigerant composed of PSMO and PSMO-CuO is proposed to cover the magnetic cooling temperature range close to room-temperature. The resulting entropy change remains practically constant between 273 K and 293 K. Such a behavior is highly appreciated from a practical point of view, particularly in cases where the cooling process is carried out by using the AMR and Ericsson cycles.
