Abstract

The microstructure of Co 5Sm crystals shows evidence of continuous precipitation with homogeneous nucleation centres of Co 7Sm 2 as well as Co 17Sm 2. The nucleation and growth mechanism, which is dependent on the lowering rate of the crystals, indicates that Co 5Sm does not decompose by a classic eutectoidal transformation. Transmission electron microscopy and microprobe analyses show regions with an inhomogeneity of the samarium concentration within and specially near the interphase boundaries of the coherently precipitated Co 7Sm 2 and Co 17Sm 2 phases. This exsolution reaction as well as the low free nucleation energy and the relatively high free activation energy below 800 °C for the diffusion process determine the magnetic properties such as the initial susceptibility and the temperature depen dence of the coercive force in Co 5Sm crystals.

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