ORIGIN OF HIGH PERMEABILITY OF NANOCRYSTALLINE FE-CU-NB-SI-B SOFT-MAGNETIC ALLOYS

The origin of the high permeability of the nanocrystalline Fe73.5Cu1Nb 3Si13.5B9 soft magnetic alloy has been studied in detail. By analysing the experimental results on the variation in permeability (mu) and co ercive force (H(c)) with annealing temperature (T(a)) in the range 500 -600-degrees-C, it has been discovered that the high peak and deep ''v alley'' in the experimental curves of mu-T(a) and H(c)-T(a) respective ly cannot be explained by a theory which considers only the low value of magneto-striction lambda(s) and the small effective anisotropy [K]. It is therefore suggested that the soft magnetic properties are also determined by a third factor DELTAM(s), which is the difference in val ue between the intensity of magnetization of the alpha-Fe(Si) phase an d that of the residual amorphous phase. Only when the values of .lambd a(s), [K] and DELTAM(s) are all small can a high permeability state be obtained. Experimental evidence is presented from the results of X-ra y, Mossbauer and magnetic measurements.