Magnetic Properties of Synthetic Mischmetal Alloyed With Cobalt, Copper, Iron, and Magnesium.
The Bureau of Mines investigated alloys containing lanthanum (la), praseodymium (pr), neodymium (nd, cobalt (co), copper (cu), iron (fe), and magnesium (mg) as possible components of a permanent magnet material utilizing a cerium-free synthetic mischmetal (m) as a substitute for scarce samarium (sm) metal. Magnets containing m- co-cu-mg and m-co-cu-fe-mg were fabricated by powder metallurgy techniques and evaluated. A synthetic mischmetal (m20) containing 20 pct la, 60 pr, and 20 nd yielded the best overall magnetic properties. The m20-co-cu-mg alloys had energy products as high as 13.2 Mgoe, remanences as high as 7.89 Kg, normal coercivities as high as 6.26 Koe, and intrinsic coercivities as high as 13.4 Koe. The best value of intrinsic coercivity, 22.9 Koe, was obtained with an m-co-cu-mg magnet in which the synthetic mischmetal contained 30 pct la, 50 pr, and 20 nd. These values compare favorably with those of the sm-co magnets fabricated and measured at the Bureau's Reno Research Center, which had energy product of 15.1 Mgoe, remanence of 7.8 Kg, normal coercivity of 7.5 Koe, and intrinsic coercivity of 27.4 Koe. Iron substitution for part of the cobalt resulted in a decrease of magnetic properties, although several percent iron can be added before a drastic loss of magnetic properties occurs.