|MadSci Network: Physics|
David, There are a variety of parameters that permanent magnet designers try to adjust with different materials. They may try to give a magnet a larger or smaller histeresis curve. Certain magnetic materials are less brittle than others. All of the materials have different behaviors with temperature. Some materials are suitable for use in the stripes on credit cards. Others are better for electric motors. This is a big industry, and there is a lot of exciting research going on. If you want specifics, I would suggest getting your local library to find you a book or two. If you search on amazon.com, for "permanent magnets" you will get a good idea of some titles. These tend to be expensive books, so the library may have trouble finding a copy. Fundamentally, all of the differences in these magnetic materials comes down to the crystalline structure, and the arrangement of electrons within that structure. These issues are typically covered in senior and graduate-level physics courses. John
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