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 (ΔTfwhm) and lower entropy changes of around 4 J/kgK which, however, puts in doubt their straightforward potential for applications as magnetocaloric materials.

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The electronic structure of Gd 1Àx Ce x Co 2 compounds with x ¼ 0.2, 0.4, 0.6, 0.75, and 0.9 is investigated by means of X-ray photoelectron spectroscopy (XPS). All investigated samples are single phase and possess a cubic MgCu 2 Laves type structure (C15). XPS core level spectra point out the intermediate valence state of Ce ions and that the Co atoms carry magnetic moments of similar magnitude in all compounds but smaller than in pure Co metal. The XPS valence band spectra of Gd 1Àx Ce x Co 2 compounds are mainly the result of the Co 3d, Ce 5d, and Ce 4f states superposition, influenced by the 3d-5d and 3d-4f hybridizations.

Magnetic properties and magnetocaloric effect under moderate magnetic field in polycrystalline Pr1-xCexCo3 compounds with x = 0, 0.1, 0.2, 0.3, and 0.4 are reported. The powder X-ray diffraction measurements show that all samples crystallize in the rhombohedral PuNi3-type structure (space group: R-3m), specific for PrCo3, with the lattice parameters decreasing with the cerium content. The magnetic measurements indicate a transition from a magnetic order state to a paramagnetic one below room temperature. The Curie temperature decreases roughly linear with the Ce concentration from 270 K for x = 0.1 to 146 K for x = 0.4. A moderate magnetocaloric effect was found for all samples, with the maximum entropy change located at temperatures near the magnetic transition ones.