Mixed Phase Behavior in Hole-Doped Perovskite Materials

MZFC, MFC magnetizations, χac susceptibility and resistance measurements have been carried out for various polycrystalline compounds of (AA’)(BB’)O3 perovskites with A = La, (Nd,Y); B = Mn,Co; A’ = Sr,Ca and B’= Fe, Ti. Analyses have been done to elucidate the metallic ferromagnetism (FM) established by Double Exchange interaction between B+3 ion and the B+4 ion that is induced by the substitution of A’ for A. It is shown that there is no ‘pure’ FM ordering existing in the compounds, in other words the materials consist of a FM and a non-FM phase. In case when the latter is an AFM phase, the coexistence and competition of the two phases result in spin-glass like appearances. Such phenomena have been observed in several compounds of both single- and/or mixed-element at B site. The studies on substitution of Mn for Co in La0.7Sr0.3Co1- yMnyO3 show no DE interaction between the two magnetic ions, which results in not only SG behavior at y = 0.1 concentration but a clear evidence on a phase separation in the high y region. An analysis of M(H,T) curves for this region suggests a structural scenario that the FM phase forms as islets (of volume fraction as small as 2.7 – 8.6%) embedded in isolating AFM matrix. For the case while B’= Ti the inhomogeneity evidence appears as an enhancement of the Low Field MagnetoResistance, which is commonly understood as an intergranular effect.