Re-entrant metallicity and magnetoresistance induced by Ce for Sr substitution in SrCoO(3-δ).

ABSTRACT

Cerium for strontium substitution allows an oxygen deficient perovskite Sr(1-x)Ce(x)CoO(3-δ) to be stabilized with a cerium solubility limited to x≤0.15 (Trofimenko et al 1997 Solid State Ion. 100 183). For these samples, the magnetic properties depend clearly upon the oxygen content Sr(0.9)Ce(0.1)CoO(2.74) and Sr(0.9)Ce(0.1)CoO(2.83) are weak and strong ferromagnets (T(C) = 160 K), respectively, the maximum ac-magnetic susceptibility of the latter being larger by two orders of magnitude than that of the former. In contrast to other Sr(1-x)L(x)CoO(3-δ) series (L =  lanthanide, Y(3) or Th(4+)), the electrical resistivity (ρ) behaviour does not simply reflect the magnetic behaviour. For x = 0.10 the re-entrant ρ feature becomes more pronounced whereas the ferromagnetic fraction and cobalt oxidation state increase. This unexpected behaviour could be related to the Ce(3+)/Ce(4+) mixed valency, the 4f localized moment of the Ce(3+) cations interacting with the conduction electrons through a Kondo-like mechanism. It is also found that the increase of oxygen vacancies favours the appearance of magnetoresistance at low T, reaching -50% at 5 K in 7 T for the Sr(0.95)Ce(0.05)CoO(2.61) sample prepared in a sealed tube.