Two useful books for reviewing the field of magnetic materials over the past 100 years are "Magnetic Induction in Iron and Other Metals," by J. A. Ewing (3rd edition, 1901), and "Ferromagnetism," by R. A. Bozorth, 1951. Appearing very nearly 100 and 50 years ago, these works summarized the field of magnetic materials in a way that no single author has since been able to achieve. In 1900, iron was the principal soft magnetic material, and hardened steel was used for permanent magnets. Most of the soft magnetic materials in use today were available in 1950; the only significant additions are the amorphous and nanocrystalline materials. However, the development of magnetically hard ferrites came mostly after 1950, as did all the development of rare-earth permanent magnets. More recent work in thin films, magnetic bubbles, magneto-optics, and magneto- resistance has all been driven by the needs of the computer industry, and often produces materials that lie between the conventional definitions of hard and soft. note
[UA01.02] Magnetic Measurements: A Century of Innovations
S. Foner (Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology)
This talk gives an historical perspective and discusses the trends of magnetic measurements over the last century. Magnetic measurements sense a force, a magnetic flux, or an indirect effect that depends on a known function of a sensor on a particular magnetic property. I will select examples from the numerous innovative approaches starting with those of Faraday, Tesla, Curie, Hall, Bitter, and Kapitza. Development of electronics enhanced the classical techniques and allowed time-dependent and microscopic measurements. Microcomputers have been combined with popular techniques in stand-alone commercial instruments. Early measurements required construction of an instrument; now many can be purchased and often high sensitivity devices are built into consumer products. Also discussed are NMR, micromachined devices, thin film magnetoresistance and spin-polarized tunneling devices, various microscopic magnetic surface probes such as scanning SQUID and magnetic force microscopy and optical probes.
[UA01.03] The Role of Quantum Mechanics in Understanding Magnetic Materials
Werner P. Wolf (Department of Applied Physics, Yale University)
The early development of quantum mechanics was closely
linked to the understanding of magnetic materials. The
effect of "crystal fields" on the properties of ions with
unfilled electron shells explained observed magnetic
susceptibilities, and the mechanism of exchange coupling
explained ordered magnetic states. Later, quantum mechanics
was used to interpret detailed microwave and optical
spectra, and the concept of the "spin Hamiltonian" was
developed. This provided a powerful tool for describing the
properties of magnetic ions and their interactions, and a
convenient starting point for the design and understanding
of new magnetic materials with a wide variety of cooperative
properties. Some of these materials became model systems for
detailed studies of critical phenomena, while others have
led to various new applications.
[UA01.04] Understanding Criticality: Magnetism as the Key
Michael E. Fisher (Institute for Physical Science and Technology, University of Maryland, College Park)
Historical episodes in the experimental and theoretical study of magnetic criticality will be described ¯ researches which, in fact, illuminated critical phenomena in all fields. The first half of this century gave us Weiss molecular-field theory, the Lenz-Ising and Bethe-Heisenberg spin chains, and Onsager's solution of the two-dimensional, zero-field Ising model. In the 50's and 60's, series expansions, reanalysis of old experiments, and new experiments, established the reality of nonclassical critical exponents. Scaling theories were demanded, formulated, and experimentally validated. Low-dimensional systems were explored. Renormalization group theory led to the understanding of anisotropic dipolar ferromagnets, tricritical points, bicriticality and crossover.
[UA01.05] Layered Magnetic Materials
Peter Gruenberg (Juelich, Germany)
This abstract not available.