Abstract

Partial substitution of Mn by a divalent metal in rare-earth manganites REMexMn1-xO3 results in the simultaneous presence of Mn3+ and Mn4+. The RE sublattice has its own properties and can interact with the local field imposed by the ferromagnetic Mn network. Its orientation differs depending on the RE nature, adopting a parallel direction with respect to the local field, or it may align in opposite direction, resulting in uncompensated antiferromagnetic structure. For divalent elements (e.g., Ni2+), the solid solution is limited to RENi2+ 0.5 Mn4+O3; at this frontier composition, the ferromagnetic superexchange Ni2+-O-Mn4+ interactions are optimized. For Me = Co, this limit can be extended, meaning that part of cobalt takes a 3+ state; in this case, presence of Co3+ modifies the magnetic coupling, leading to qualitatively different behaviours during the ZFC/FC cycles. In this work, we have chosen the specific composition REMe0.50Mn0.50O3 for which the strongest magnetic interactions are expected, emphasizing the results obtained for Me = Ni and Co and comparing various rare-earth elements (RE = Y, La, Pr, Nd, Eu, Gd and Er). As expected from the general behaviour of the series (RE,Ca)MnO3, we find that in the RE(Mn,Me)O3, the larger the RE ionic radius, the highest the transition temperature, reaching 235 K in LaCo0.50 Mn0.50O3 compared to 68 K in ErCo0.50 Mn0.50O3.