D. Gignoux

Soft Materials for Electrical Engineering and Low Frequency Electronics

The materials presented in this chapter are used at low frequencies, i.e. below 400 Hz for power electrical engineering, and 100 kHz for power electronics. After a general presentation which will include a detailed discussion on the origin of magnetic dissipation, we will discuss the various families of soft steels, of ferrites, and high or very high permeability alloys, from the oldest steels which date back to the nineteenth century to the newcomers, viz the amorphous and nanocrystallized materials. We will finally review the low frequency applications of these soft materials.

Practical Magnetism and Instrumentation

The first part of this chapter covers the techniques used for the measurement of soft or hard materials. The second part treats the generation of magnetic fields, whilst their measurement is described in the third and final part.

Magnetism of Earth Materials and Geomagnetism

The discovery of the earth’s magnetic field belongs to the origins of physics. Although less well known than the beginnings of astronomy and celestial mechanics associated with Copernicus, Galileo and Newton, its history is nevertheless exemplary of the development of science. It was the existence of a real need by society (precise navigation using the magnetic compass),the experimental deduction by Gilbert, and the problem of the rationalization of action at a distance (the only scientific example for a long time being the force between magnets) that were responsible for this early progress. The demonstration by Gilbert in 1600 of the internal origin of the earth’s magnetic field based on the similarity of the lines of force around the earth and those around a naturally magnetic sphere of lodestone, is considered to be the first publication of modern physics, even before the solution by Galileo of a body falling under gravity. This internal origin along with the mystery of action at a distance probably contributed to the “diabolization” of magnetism during the following centuries.

Magnetism and the Life Sciences

The curiosity of “magneticians” has recently extended to magnetic substances synthesised by some living organisms: bacteria, bees, pigeons,dolphins. . . The list gets longer every year. This is one aspect of magnetobiology, which also studies the influence of magnetic fields on the growth of plants or on animal metabolism. The magnetic properties of organic matter, whether living or inert, will be treated in the first part of this chapter.

Magnetic Thin Films and Multilayers

Progress in high vacuum and ultra high vacuum material preparation techniques now allow the preparation of artificial structures consisting of ultra thin films of magnetic materials, as well as multilayer systems containing stacks of different materials, some of which being magnetic. In addition,many techniques are also now available for both the structural and magnetic characterization of these systems.

Principles of Magnetic Recording

Magnetic recording is based on remanence, i.e. on the possibility of writing stable or metastable magnetization configurations within a material. The information carrying medium is the heart of any recording (or storage) system. Of course it is complemented by write, erase, and readout devices.

Soft Materials for High Frequency Electronics

Electronics is different from power electrical engineering in two major respects. The range of frequencies involved is typically restricted to 1 kHz in power electrical engineering, whereas it extends to the microwave regime, beyond 1 GHz, in electronics. The excitation level of magnetic materials is near saturation in power electrical engineering, leading to very large non-linear effects, while it remains usually much lower in electronics, where the linear regime prevails since the signals have low amplitude. While power electrical engineering mainly uses ferromagnetic alloy sheets, good conductors of electricity, the favorite materials of electronics are ferrimagnetic oxides, with insulator or semiconductor electrical character.