Spinodal decomposition and magnetic properties of Fe–Cr–12Co permanent magnet alloys

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Abstract
This report is concerned with the spinodal decomposition and magnetic properties of Fe–21∼30 Cr–12Co ternary alloys (by weight) as studied by transmission electron microscopy and magnetic measurements. Wavelength growth of the isothermally aged spinodal structure is found to be proportional to time1/3 for the later stage of aging at all aging temperatures, which suggests a coarsening process. Spinodal temperatures of these alloys are found to be higher than each of their Curie temperatures; nevertheless magnetic aging is effective in greatly improving the magnetic properties. Hence, a prerequisite of a higher Curie temperature in the magnetic aging theory is concluded to be unnecessary. Moreover, as the extrapolated onset spinodal wavelength, of 80–100 Å, is superparamagnetic in nature, this suggests a prerequisite for the magnetic aging theory. Before magnetic aging can be operative, the particle should grow to a certain critical size, determined by the aging temperature and the anisotropy energy at that temperature, in order to have thermally stable magnetization.