New Permanent Magnet Materials Containing Rare-Earth Metals

Abstract

Previously, most basic magnetic properties of the hexagonal intermetallic compounds involving the rare‐earth (RE) and 3‐d transition elements were reported in the literature. In addition, some of these compounds were investigated by various workers for permanent magnet properties by grinding ingots of the compounds into very fine powder. Recently, we discovered new permanent magnet materials which were based mostly on the hexagonal intermetallic compounds Co₅RE. Replacement of cobalt with copper in some of these rare‐earth compounds resulted in solid materials having substantial permanent magnet properties. An outstanding feature of these alloys is their high value of intrinsic coercive force. High‐energy product alloys were found in the Co_5−xCu_xSm and Co_5−xCo_xCe systems with iron additions. Small pieces of Co_3.5Fe_0.4Cu_1.35Sm exhibited B_R=6450 G, B^H_C=4000 Oe, and (BH)_m=9×10⁵ G Oe. Also, small pieces of Co_3.5Fe_0.5CuCe exhibited B_R=5100 G, B^H_C=3500 Oe, and (BH)_m=5.2×10⁶ G Oe. In general, these alloys are prepared by inert‐electrode arc melting, resulting in a relatively rapid freezing from the molten state. The samples are then given a low‐temperature anneal. Cross sections of the specimens show microstructural directionality which is a result of freezing in a direction normal to the cold surface of the hearth. These directional effects appear to be associated with the directional magnetic properties that are important because of the high crystal anisotropy of the alloys. When a specimen of the composition Co_3.45Fe_0.25Cu_1.35Sm was annealed at 1100°C and examined by optical‐microscope and electron‐probe techniques, particles rich in Co₅Sm were observed to be embedded in a Cu₅Sm‐rich matrix. The iron appeared largely in the cobalt‐rich phase. The cobalt‐rich particles were approximately 2.5×10 μ. Further work is in progress to improve directional properties and thus further improve the magnetic properties.