Influence of A-site ionic radii on the structural, magnetic and magnetocaloric properties in Nd0.85Me0.15MnO3 (Me = Ca, Sr, Ba) manganites

The influence of the average cation radius in the A-site (< r(A)>) and the cation disorder parameter (sigma(2)) on the structural, magnetic and magnetocaloric properties of manganites with low fixed hole concentration Nd0.85Me0.15MnO3 (Me = Ca, Sr, Ba) was studied using X-ray diffraction, magnetometry and differential thermal analysis methods. It was found that an increase in < r(A)> leads to a decrease in orthorhombic distortions, an increase in the unit cell parameters, the length of the Mn-O valence bond, and the values of the Mn-O-Mn valence angle. An increase in the disorder parameter sigma(2) contributes to the destruction of orbital ordering and weakening of the cooperative Jahn-Teller effect. The temperatures of magnetic transitions (T-C) in the Mn and Nd sublattices were determined. The correct expression was proposed for the bandwidth W similar to T-C which took into account the parameters Mn-O and Mn-O-Mn, based on which the T-C(Mn) in Nd0.85Me0.15MnO3 (Me = Ca, Sr, Ba) was estimated. It was shown that the maximum entropy change (-Delta S-max) and the relative cooling power (RCP) demonstrated a linear dependence on the applied magnetic field. The RCP values also obey a linear dependence on the parameters < r(A)> and sigma(2). The obtained RCP values for Nd0.85Ca0.15MnO3 and Nd0.85Sr0.15MnO3 are larger or of the same order as in the case of Gd.