The Effect of Pr Doping and Sintering Temperature on The Structural, Magnetic and Transport Properties of La_1-x-yPr_yCa_xMnO₃ (y = 0.30, 0.35, 0.40; x = 0.40) Nanocrystals

Among the doped rare earth manganites, La_1-<i>x-y</i>Pr<i>_x</i>Ca_yMnO₃ (LPCMO) has been recognised as the prototypical of the phase separated doped rare-earth manganites. LPCMO perovskite manganites still attract the interest of materials, chemistry and physics communities. The structural, microstructural, magnetic and electrical transport properties have been correlatively studied to decipher the complex consequences of variation of intrinsic parameter, the average La-site cationic radii and extrinsic particle size on the magneto-electrical phase coexistence in La_1-<i>x-y</i>Pr<i>_y</i>Ca<i>_x</i>MnO₃ (<i>y</i> = 0.30, 0.35, 0.40; <i>x</i> = 0.40). Magnetization measurements show sequential paramagnetic (PM)-antiferromagnetic (AFM)-ferromagnetic (FM) transitions on lowering the temperature. The AFM-FM transition exhibits (i) pronounced hysteresis between field-cooled cooling (FCC) and field-cooled warming (FCW), (ii) substantial divergence between zero-field cooling (ZFC) and FCW curves. The lower temperature magnetic state is much closer to a spin glass at smaller ionic radius and larger particle size. At smaller ionic radius and smaller particle size, it shows a better resemblance to a cluster glass state. The presence of a large thermal hysteresis in the insulator-metal transition (IMT) coupled with the one in FCC-FCW magnetization at particle sizes ~200 nm-160 nm, and ~460-400 nm demonstrates that this particle size regime is the most conducive to the phase separation. IMT disappears at smaller ionic radii and larger particle sizes due to the enhancement of AFM and charge-ordering. The observed phenomena are explained in terms of the interplay between the ionic radii and particle size induced changes in the average apical bond angles and the average bond length.