Preparation of La0.7Ca0.3-xSrxMnO₃ Manganites by Four Synthesis Methods and Their Influence on the Magnetic Properties and Relative Cooling Power.

María Botello-Zubiate,Daniel Soto-Parra,María Grijalva-Castillo,José Matutes-Aquino,Carlos Santillán-Rodríguez,Renee Sáenz-Hernández

doi:10.3390/ma12020309

Abstract

Manganites of the family La0.7Ca0.3−xSrxMnO3 were fabricated by four preparation methods: (a) the microwave-assisted sol-gel Pechini method; (b) sol-gel Pechini chemical synthesis; (c) solid-state reaction with a planetary mill; and (d) solid-state reaction with an attritor mill, in order to study the effect of the preparation route used on its magnetocaloric and magnetic properties. In addition, the manganites manufactured by the Pechini sol-gel method were compacted using Spark Plasma Sintering (SPS) to determine how the consolidation process influences its magnetocaloric properties. The Curie temperatures of manganites prepared by the different methods were determined in ~295 K, with the exception of those prepared by a solid-state reaction with an attritor mill which was 301 K, so there is no correlation between the particle size and the Curie temperature. All samples gave a positive slope in the Arrot plots, which implies that the samples underwent a second order Ferromagnetic (FM)–Paramagnetic (PM) phase transition. Pechini sol-gel manganite presents higher values of Relative Cooling Power (RCP) than the solid-state reaction manganite, because its entropy change curves are smaller, but wider, associated to the particle size obtained by the preparation method. The SPS technique proved to be easier and faster in producing consolidated solids for applications in active magnetic regenerative refrigeration compared with other compaction methods.

Highlights

IntroductionMagnetic refrigeration, based on the magnetocaloric effect, is a promising technology due to its greater cooling efficiency, the possibility of building more compact (even portable) devices, and because it is environmentally friendlier than the conventional cooling processes based on the compression and expansion cycles of gas [1]
Magnetic refrigeration, based on the magnetocaloric effect, is a promising technology due to its greater cooling efficiency, the possibility of building more compact devices, and because it is environmentally friendlier than the conventional cooling processes based on the compression and expansion cycles of gas [1]
The ability to tune the Curie temperature, as well as the ability to build a multiple-material regenerator in a practical way [14,15] makes the manganites important materials for use in magnetic refrigeration devices

Summary

Introduction

Magnetic refrigeration, based on the magnetocaloric effect, is a promising technology due to its greater cooling efficiency, the possibility of building more compact (even portable) devices, and because it is environmentally friendlier than the conventional cooling processes based on the compression and expansion cycles of gas [1]. The ability to tune the Curie temperature, as well as the ability to build a multiple-material regenerator in a practical way [14,15] makes the manganites important materials for use in magnetic refrigeration devices. Numerous investigations have been carried out on the effect of the preparation method in the magnetic and magnetocaloric properties of manganites [1,11,16,17,18,19,20]. Curie temperature to values closer to room temperature This is important for application in magnetic refrigeration, but at the expenses of a lower MCE [21]. La(Ca,Sr)MnO manganites were fabricated by four different preparation methods: microwave-assisted sol-gel Pechini synthesis, sol-gel Pechini chemical synthesis, a solid-state reaction route with a planetary mill, and a solid-state reaction route with an attritor mill, each obtaining different morphologies, particle sizes, and chemical compositions which exert their influence on magnetocaloric properties

Materials and Methods

Results and Discussion

Powder

Thermomagnetic

Conclusions