The effects of Al on the magnetic properties of nanocrystalline Fe73.5−XAlXSi13.5B9Cu1Nb3 alloy ribbons, where 0⩽X⩽10, are reported for the first time. The evolution of the structure and magnetic properties of the ribbons, which were initially cast into the amorphous state in an inert gas environment at subatmospheric pressure, were studied as a function of annealing temperature Tann. The minimum dc coercivity developed during annealing, Hcmin, was found to decrease significantly with increasing Al content from 0.5 A/m at X=0 to 0.3 A/m at X=2 and to remain at approximately this level over the range 2<X⩽8 before rising to 0.4 A/m at X=10. The saturation polarization, Js, was, however, found to decrease linearly over this range from Js=1.5 T at X=0 to Js=0.9 T at X=10 for samples exhibiting Hcmin. As there was little significant reduction in the mean crystallite size, dg, at Hcmin with increasing X, this decrease in coercivity was considered to result from a reduction of the magnetocrystalline anisotropy, K1, of the crystallites as a result of the incorporation of Al.

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