Important role of impurity eg levels on the ground state of Mn-site doped manganites

The comparative study of the doping of the CE-type antiferromagnet Pr0.5Ca0.5MnO3 with 5% of different elements shows that two classes of materials can be generated from the viewpoint of the transport and magnetic properties in the absence of a magnetic field, depending on the electronic configuration of the dopant. The first class corresponds to the formation of spin glass like insulators and is obtained for dopants without d orbitals (Al3+, Mg2+) or with a d(0) configuration (Sc3+, Ti4+) or a d(10) configuration (Ga3+, In3+, Sn4+). In this class, the doping element destroys the long range charge ordering but does not participate in the ferromagnetic coupling. The second class is obtained for magnetic cations having their d orbitals partially occupied (Cr3+, Rh3+, Ru4+ or Ru5+, Ni2+, Co2+). In these oxides. the dopant participates in the band formation. broadening the bandwidth so that both metallicity and ferromagnetism are induced. Among all the investigated elements, Fe3+ appears as a special case since it belongs to the first class in spite of its d(5) configuration. This different behavior is explained by the great stability of the high spin t(2g)(3)e(g)(2) configuration of Fe3+. (C) 2002 Elsevier Science Ltd. All rights reserved.