Ion beam sputtered thin films of finemet alloy for soft magnetic applications

Amorphous films of finemet composition (Fe73.9Cu0.9Nb3.1Si13.2B8.9) have been prepared using ion-beam sputtering of a target made out of amorphous ribbons of same composition. Effect of film thickness on the magnetic anisotropy as well as coercivity has been studied. It is suggested that domain wall pinning at surface irregularities as well as random stresses may significantly affect the coercivity. Nanocrystallisation of the film by controlled thermal annealing results in significant change in coercivity, which can be understood in terms of the random anisotropy model. Irradiation of amorphous film by 120 MeV Ag+ ions results in a significant decrease in coercivity. This may be correlated with improvement in the surface smoothness and possible relaxation of random stresses. Present results show that swift heavy ion irradiation (SHI) can be effectively used as a tool to improve the soft magnetic properties of thin films.