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The effect of substituting Fe by Co on the crystallization, structural and magnetic behaviour of Fe(72-x)Co(x)Si4B20Nb4 (X = 10, 20, 36, 50 at%) and Co36Fe36Si(4-Y)Al(y)B20Nb4 (Y = 0, 1 at%) alloys prepared in the form of melt spun ribbons has been discussed. Alloys containing optimum content of cobalt = 36 at% showed consistent coercivity at elevated temperatures. This soft magnetic property was further improved with aluminium incorporation. Transmission electron microscopy (TEM) indicated that such enhancement in the properties was due to finer dispersions of (CoFe)SiAl nanoparticles in amorphous matrix. Nanocrystallisation also raised the Curie temperature of the aluminium contained alloy.

This investigation addresses the effect of nanocrystallization on ferromagnetic ordering in a series of (Fe72−XCox)Si4B20Nb4, (X = 10, 20, 36, 50 at%) alloy ribbons prepared by the melt-spinning technique. Partial substitution of Fe by Co throughout this series affected the primary and secondary crystallization onsets observed from differential scanning calorimetry and the consequent generation of bcc-FeCo and (CoFe)3B, respectively, as observed from x-ray diffractometry. The reduction in the size of nanoparticles with increasing cobalt content was observed from transmission electron microscopy. At an elevated temperature, the alloy with X = 36 at% was found to reveal superior soft magnetic properties compared with other alloys. In the nanostructured state, this alloy also showed enhanced ferromagnetic ordering and low power losses exhibited its scope as a material for high temperature soft magnetic application.