We have measured the total magnetic losses of Fe-6.4wt%Si, amorphous F
e78B13Si9 and amorphous and nanocrystalline Fe73.5Cu1Nb3Si13.5B9, in t
he range 1-10(3) Hz. The total loss was found to be lowest in nanocrys
talline Fe73.5Cu1Nb3Si13.5B9. We have applied Bertotti's formalism for
this alloy in both amorphous and nanocrystalline forms. The experimen
tal loss data were well reproduced with V0 = 0.18-0.20 A/m for amorpho
us ribbons and with V0 = 0.12 A/m for nanocrystalline ribbons.