ABSTRACT
It is widely known that metal oxides show a variety of phenomena, such as magnetism, dielectorics, superconductivity, etc., which are remarkably sensitive to their chemical compositions, crystal structures, carrier concentrations, and also the applied external fields. The studies of magnetic and optical properties in metal oxides long time ago, from the view point of fundamental aspects as well as applications [1]. The discovery of the high transition-temperature superconducting (HTSC) cuprates in 1986 [2] was a milestone in the study of metal-oxides. The method of synthesing single large crystals has been greatly developed, and systematic transport, optical and diffraction measurements have also become a matter of concern. Also, a lot of exotic physical concepts have been proposed by the theoretical examinations. Following the discovery of HTSC cuprates, metal oxides has been studied from the modern point of view. One of the most attractive compounds after HTSC cuprates is the manganites with the
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perovskite structure. Study of the perovskite manganite started as early as the 1950s [3], and recently the massive reduction of the electric resistivity applying the magnetic field — the so-called colossal magnetoresistance (CMR) — was discovered [4-7]. A common physics concept in these two oxides is the electron correlation, that is, the many-body nature of 3d electrons in the metal ions. In this chapter, among a number of metal oxides, we consider two representative oxides, that is, the HTSC cuprates and the CMR manganites, and introduce themagnetic and the optical properties from the viewpoint of the electron correlation.
