4. Magnetic Properties of Electronic Materials

This work reviews basic concepts from both traditional macroscopic magnetism and unconventional magnetism, in order to understand current and future developments of submicronic spin-based electronics, where the 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 localised d electronic states). While this picture might be enough to understand some aspects of traditional storage and electromechanics, it is not sufficient when describing condensed matter systems with smaller length scales (progressing toward the nanometer range). In this case, the precise nature of the magnetism (localized, free or itinerant as in Fe, Co and Ni transition metals) should be accounted for, along with the simultaneous presence of charge and spin on carriers. In addition, when we deal with the thin films or multilayers found in conventional electronics, or with objects of reduced dimensionality (such as wires, pillars, dots or grains), the magnetic properties are expected to be different from conventional three-dimensional bulk systems.

This chapter is organized as follows. We begin (in the Introduction) by highlighting the new era of submicronic spin-based electronics, and we present a table of papers on the topics we cover in the chapter, for the reader who wishes to learn more. The traditional elements of magnetism, such as the hysteresis loop, conventional types of magnetism and magnetic materials, are then presented (in Sect. 4.1). We then briefly describe (in Sect. 4.2) unconventional magnetism, which can be used to understand new high-tech materials that will be used in future devices based on spintronics and quantum information.