Mn-site doping induced CMR properties in calcium rich manganites Pr_1‒xCa_xMnO₃(0.6 ≤ x ≤ 0.7)

Abstract:

Doping of Mn-site by chromium, cobalt and nickel has been investigated in the calcium rich manganites Pr_0.4Ca_0.6MnO₃ and Pr_0.3Ca_0.7MnO₃. Whatever the nature of the doping element, a rapid disappearance of the charge ordered (CO) state is observed, T _CO decreasing as the doping rate increases. But the most important result concerns the Cr-doped compounds Pr_0.4Ca_0.6Mn_1‒x Cr _x O₃ for which a re-entrant insulator to metal transition at 90-120 K is observed for x = 0.10‒0.12, in a zero magnetic field. The possibility to induce colossal magnetoresistance (CMR) properties for high Mn(IV) contents (Mn(IV)/Mn(III) ≥ 3/2) for x = 0.07‒0.12 is shown for the first time, the resistance ratios |R₀/R_7T reaching 2 × 10₆ at 30 K. This study also shows differently that the small size of the A-site cation (Pr, Ca) is not a redhibitory obstacle to the appearance of CMR properties in manganites, in contrast with previously established phase diagrams.