Effect of the A-Site Randomness on Magnetotransport Properties of PrBaMn₂O₆ Manganites

A-site ordered PrBaMn2O6 manganites were obtained by a two-step synthesis process. The chemical composition, crystal structure, magnetic and magnetotransport properties have been investigated with regard to the degree of ordering of the Pr3+ and Ba2+ cations. A-site disordered Pr0.50Ba0.50MnO3 has a cubic perovskite-like unit cell (SG = Pm3m , Z = 1), while the A-site ordered PrBaMn2O6 has a tetragonal unit cell (SG = P4/mmm, Z = 2). The A-site ordered state in PrBaMn2O6 remains stable on heating to 1300 0C in an oxidizing medium (P[O2] = 1 bar). The cation ordering leads to a significant increase in the critical temperatures of phase transitions. Asite ordered PrBaMn2O6 is a metallic ferromagnet with the TC ~ 320 K, whereas TC of a fully disordered sample is ∼ 140 K. The samples with intermediate degrees of ordering contain two magnetic phases. Slightly below TC, all samples exhibit a metal–insulator transition and a peak of the magnetoresistance, amounting to approximately 10 % and 65 % in a magnetic field of 9 kOe for the fully ordered PrBaMn2O6 and disordered Pr0.50Ba0.50MnO3, respectively. The results are interpreted in terms of the degree of ordering of the Pr3+ and Ba2+ cations.