Crystallization of FeB alloys with rare earths to produce hard magnetic materials (invited)

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Abstract
Among the first crystallized melt quenched alloys to exhibit interesting hard magnetic properties was (Fe0.82B0.18)0.9Tb0.05La0.05. The high coercive force of this alloy results from a mixture of R6Fe23 and Fe3B phases with a very fine grained microstructure (∼300 Å). The hard magnetic state only exists over a narrow range of annealing temperatures due to phase decomposition and grain growth at higher temperatures. Recent results on alloys with compositions corresponding to varying ratios of R6Fe23 and Fe3B have suggested a new magnetically hard ternary phase near the composition R0.15Fe0.783B0.067. In contrast to earlier alloys, the hard magnetic state of this material remains essentially unchanged over a rather wide range of annealing temperatures up to at least 800 °C. When R is mostly Nd or Pr, isotropic magnets with energy products as high as 13 MGOe can be produced.