4. Magnetic Properties: From Traditional to Spintronic

This chapter reviews basic concepts used in the traditional macroscopic magnetism in order to understand current and future developments of submicronic spin-based electronics where interplay of electronic and magnetic properties is crucial. Traditional magnetism is based on macroscopic observation and physical quantities are deduced from classical electromagnetism. Physical interpretations are usually made with reference to atomic magnetism where localized magnetic moments and atomic physics prevail, despite the fact that standard ferromagnetic materials such as Fe, Co, and Ni are not localized-type magnets (they have extended s and localized d electronic states). While this picture might be enough to understand some aspects of traditional storage and electromechanics, it is no longer sufficient for the description of condensed matter systems with smaller length scales progressing toward the nanometer range. The precise nature of magnetism (localized, free, or itinerant like Fe, Co, and Ni transition metals) with simultaneous presence of charge and spin of carriers should be considered. In addition, when we deal with thin films or multilayers as in conventional electronics or with reduced dimensionality objects such as wires, pillars, dots, or grains, magnetic properties are expected to be different from three-dimensional conventional bulk systems.