Magnetism and Magnetic Measurements

Abstract

Abstract This article introduces the sections on magnetism and magnetic measurements. Magnetism and magnetic materials have a long and illustrious history. Lodestone (a variety of magnetite) was the first magnetic material of technological importance—which often means military importance as well—due to its seemingly mystical power of seeking direction, a feat which never fails to fascinate a first‐time observer. Lodestones were known to the ancient Egyptian, Greek, and Chinese civilizations, and possibly others. About 2600 B.C., lodestone was instrumental in winning a decisive battle for the first emperor of China, fought in a dense fog against the invading barbarians. The subject that we generally call magnetism began with the observation that some minerals, such as magnetite, could attract each other and certain other minerals. However, a fundamental understanding of magnetism had to await the advent of quantum mechanics and special relativity in the 20th century. Today, magnetism enters many aspects of our lives, far beyond just compasses and refrigerator magnets. Magnetic materials and magnetic phenomena inconspicuously appear in many complex devices, for example, theft‐prevention systems in department stores, magnetic recording disks and read heads in the ubiquitous computers and cellular phones, and in magnetic resonance imaging apparatus. Some of the more exciting new developments are the spintronic devices, which are on the verge of becoming realities. These new devices are based on the spin properties of electrons, as opposed to charge alone, as in conventional electronics. The subject of magnetism is inseparable from electrical charges, their translational motion and their angular momenta. The articles in this category cover magnetic fields and properties, measurement of magnetic fields and their effect on materials behavior.