## ABSTRACT

Recent extensive studies on the manganese oxides with perovskite or layeredperovskite structures have shown that a close interplay among spin, charge and or­ bital (crystal lattice) degrees of freedom is quite important for understanding many unconventional physical properties of these oxides. The perovskite manganites are in general formulated as R E \-X AZ^MnOs, where RE and A E are a trivalent rare earth and an alkaline earth element, respectively. In REMnOs (x = 0), the electron configuration of (3d4; is realized for the Mn3+ site, and due to ordering of eg-orbital (or cooperative Jahn-Teller distortion [1-4]) the substance is a layered (or A-type) antiferromagnetic insulator. In R E \-xAExMn0 3 , Mn4+ (3d3; t^e®) is created by the substitution of R E with A E and holes are accordingly introduced in the eg-band. In Lai-^Sr^MnOs and Lai-jCa^MnC^, which have long been known as conducting ferromagnets [5-7], the mobile ^-electrons mediate the ferromagnetic interaction between the neighboring Mn3+ and Mn4+ sites, which is termed double exchange interaction [8-10].