Magnetic Properties and Magnetocaloric Effect of Polycrystalline and Nano-Manganites Pr0.65Sr(0.35-x)CaxMnO3 (x ≤ 0.3)

Here we report investigations of bulk and nano-sized Pr0.65Sr(0.35-x)CaxMnO3 compounds (x <= 0.3). Solid-state reaction was implemented for polycrystalline compounds and a modified sol-gel method was used for nanocrystalline compounds. X-ray diffraction disclosed diminishing cell volume with increasing Ca substitution in Pbnm space group for all samples. Optical microscopy was used for bulk surface morphology and transmission electron microscopy was utilized for nano-sized samples. Iodometric titration showed oxygen deficiency for bulk compounds and oxygen excess for nano-sized particles. Measurements of resistivity of bulk samples revealed features at temperatures associated with grain boundary condition and with ferromagnetic (FM)/paramagnetic (PM) transition. All samples exhibited negative magnetoresistivity. Magnetic critical behavior analysis suggested the polycrystalline samples are governed by a tricritical mean field model while nanocrystalline samples are governed by a mean field model. Curie temperatures values lower with increasing Ca substitution from 295 K for the parent compound to 201 K for x = 0.2. Bulk compounds exhibit high entropy change, with the highest value of 9.21 J/kgK for x = 0.2. Magnetocaloric effect and the possibility of tuning the Curie temperature by Ca substitution of Sr make the investigated bulk polycrystalline compounds promising for application in magnetic refrigeration. Nano-sized samples possess wider effective entropy change temperature (Delta T-fwhm) and lower entropy changes of around 4 J/kgK which, however, puts in doubt their straightforward potential for applications as magnetocaloric materials.

Automated summary

This study investigates the properties of bulk and nano-sized Pr0.65Sr(0.35-x)CaxMnO3 compounds. Different methods were used for their synthesis. X-ray diffraction reveals a decrease in cell volume with increasing Ca substitution. Optical and transmission electron microscopy were used to study the morphology. The resistivity measurements show features related to grain boundary and ferromagnetic/paramagnetic transition. The Curie temperature decreases with increasing Ca substitution. Bulk samples show high entropy change, making them promising for magnetic refrigeration applications, while the potential of nano-sized samples as magnetocaloric materials is uncertain.