Pr doping at the A-site of LaBaMnO nanocrystalline material: assessment of the relationship between structural and physical properties and Bean-Rodbell model simulation of disorder effects.

Bulk nanocrystalline samples of (La Pr )BaMnO (0.075 ≤ ≤ 0.30) manganites with a fixed carrier concentration are prepared by the sol-gel based Pechini method. Rietveld refinement of the X-ray diffraction patterns, shows the formation of single-phase compositions with rhombohedral symmetry. Upon Pr doping at the A-site, the unit cell volume and the B-O-B bond angles are reduced. FTIR spectra present a prominent absorption peak of the in-phase stretching mode (B mode) rising from the vibration of the Mn-O bond. Raman spectra at room temperature reveal a gradual shift toward lower frequencies in (E) phonon mode with increasing Pr concentration. The () measurements shows a clear ferromagnetic (FM)-paramagnetic (PM) phase transition with increasing temperature. An increase in resistivity and activation energy and a decrease in the metal-semiconductor transition ( ) and Curie temperatures ( ) was observed as a consequence of Pr doping. The results are discussed according to the change of A-site-disorder effect caused by the systematic variations of the A-site average ionic radius 〈 〉 and A-site-cation mismatch , resulting in the narrowing of the bandwidth and the decrease of the mobility of e electrons. The magneto-transport behavior in the whole measured temperature and a magnetic field can be described by a percolation model, which is in agreement with the limited experimental data of the samples for = 0.075, 0.15 and 0.30. The experimental results confirm that A-site substitution with Pr destroys the Mn-O-Mn bridges and weakens the double exchange (DE) interaction between the Mn (t e , = 2) and Mn (t e , = 3/2) ions. On the other hand, the Bean and Rodbell model has been successfully used to simulate the magnetization data of the samples with = 0.15 and = 0.22. The random replacement of La by Pr is shown to induce more disorder in the system, which is reflected in the increase of the fitted disorder parameter and spin value fluctuation. At a temperature close to room temperature, the maximum magnetic entropy change (Δ ) and the relative cooling power (RCP) of LaPrBaMnO are found to be, respectively, 1.34 J kg K and 71 J kg for a 1.5 T field change.