New permanent magnet materials containing rare-earth elements (RE) have been discovered. For the most part, these alloys are based on the hexagonal intermetallic compounds, Co5RE. Replacement of cobalt with copper in some of these rare-earth compounds results in solid materials with substantial permanent magnet properties. Coercive forces as high as 28,700 Oe have been obtained in heat-treated samples of alloys in the Co5Sm–Cu5Sm system.

The effect of adding the rare-earth elements to cobalt, iron, and nickel has been investigated. Antiferromagnetic coupling was found to exist in the cobalt and iron rare-earth compounds. The moment per formula unit of the compound Co5Y is increased when Sm, Pr, and Nd are substituted for yttrium and decreased when Tm, Gd, Tb, Er, Dy, and Ho are substituted. This is explained on the basis that although the spin moments of cobalt and rare earths are coupled antiferromagnetically in these compounds, the orbital moments add to the cobalt moment in the compounds containing Sm, Pr, and Nd, but they subtract from the cobalt moment in the compounds containing Tm, Tb, Er, Dy, and Ho. For the iron compounds investigated, the moment of the compound Fe4Y was found only to decrease when Tm, Er, Ho, and Dy were substituted for yttrium. The nickel compounds behaved entirely differently from the cobalt and iron compounds since very little or no antiferromagnetic coupling was observed in these compounds.

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This paper deals with the results of an electron diffraction investigation of the structure of soft magnetic materials which exhibit magnetic annealing. The property of heat treatment in a magnetic field has been found to depend upon the oxygen content present as an impurity and is associated with distinct diffraction phenomena. A structural model based on an interpretation of diffraction results, magnetic properties, and oxygen content is presented. The pertinent conclusions from this study are: 1. The ability of soft magnetic alloys containing Fe, Co, and Ni to exhibit magnetic annealing properties is due to oxygen present as an impurity. 2. An oxygen content of about 0.001% is sufficient to produce magnetic annealing with the proper heat treatment. An alloy containing only 0.0001% oxygen fails to respond to field heat treatment or is ``dead.'' 3. The oxygen impurity produces magnetic activity in the alloy crystal (with proper heat treatment) by condensing into the (111) planes of the crystal, thus giving rise to a stacking disorder or fault. The term ``impurity fault'' has been introduced to describe this structural irregularity. 4. The oxygen impurity faults are presently thought to be aligned by magnetic annealing and are intimately connected with field heat treatment properties. If sufficient oxygen is available in the crystal, the faults thicken and organize to yield metal oxides.