Magnetic Materials, Bulk

Abstract

Magnetism is classified according to the nature of the bulk magnetic response in a magnetic field. Types of magnetism are defined as are the terms of magnetic behavior. Bulk magnetic materials may be classified as either soft or hard. The important soft magnetic materials, characterized by high permeability and low coercivity, include iron and low carbon steel, iron–silicon alloys, iron–aluminum and iron–aluminum–silicon alloys, cobalt–iron (Permendurs) and nickel–iron alloys (Permalloys), ferrites, and amorphous magnetic alloys. The iron‐based alloys are used for power distribution transformers and magnetic shielding. The ferrites are used at high frequencies for inductors and communication transformers as well as for microwave devices. Moreover, the use of MnZn ferrite cores in power transformers is increasing rapidly. The hard of permanent magnet materials are characterized by high coercivity and high energy product. Materials in use include the hexagonal barium and strontium ferrites, alnicos, the modified binary cobalt‐base intermetallics containing rare earths, and the ternary neodynium iron‐base intermetallics. Motors, loudspeakers, and disk drives are the largest consumers of hard magnetic materials. The exceptionally large values of maximum energy products and coercivities of the Nd–Fe–B magnets permit use in devices where small size and superior performance are desired. Many of the semihard permanent magnet materials are sufficiently ductile for forming into requisite shapes. Information is presented for several important materials which can be cold formed, rolled to thin foil, and can be stamped into precision parts at high speeds.