  In this article we give a general survey of the main properties of magnetic
oxides - mostly the oxides of transition metals, but sometime also containing
rare earths ions. This is a very rich class of materials, among which there are
insulators and metals, systems with insulator-metal transitions, and there are
among them even high-temperature superconductors. One of the main features of
these compounds, which attract to them special attention and which serve as a
basis of many applications, are their rich magnetic properties. In this article
we discuss the main physical effects determining their behaviour, and describe
in detail especially their magnetic properties, but not only. After shortly
discussing the basic structure of isolated magnetic ions, we concentrate on the
collective effects depending on the interaction between sites, especially
exchange interaction, giving rise to different magnetic properties: different
types of magnetic ordering in conventional systems, but also more exotic states
such as spin liquid states in frustrated systems. We also cover related
phenomena in magnetic oxides, such as magnetoelectric and multiferroic
behaviour, and discuss at the end their diverse useful properties serving as a
basis of many applications.
