Influences of Ru-doping on the magnetic properties of Ca0.85Pr0.15Mn1-xRuxO3

CaMnO3 is an antiferromagnet, in which the super-exchange interaction taking place between Mn4+ ions plays an important role. The doping of a small amount of 15% Pr into the Ca site, Ca0.85Pr0.15MnO3, leads to the appearance of Mn3+ ions, and introduces the ferromagnetic (FM) double-exchange interaction between Mn3+ and Mn4+ ions, which is dominant in a narrow temperature range of 90 ∼ 115 K. The FM interaction becomes strong for Ca0.85Pr0.15MnO3 doped with 4 and 8% Ru into the Mn site (i.e., Ca0.85Pr0.15Mn1-xRuxO3 with x = 0.04 and 0.08). The Curie temperature obtained for x = 0.04 and 0.08 are about 135 and 180 K, respectively. While the FM interaction in the former is dominant due to Mn3+-Mn4+ exchange pairs, the latter has the contribution of Ru ions. This results in remarkable differences in the features of their FM-paramagnetic phase transitions and their coercive fields Hc.