Soft magnetic properties and heat stability for Fe/NiFe superlattices

Abstract

Soft magnetic properties and heat stability were investigated for Fe/NiFe (91 wt.% Ni and 19 wt.% Fe) superlattice films. X-ray diffraction data show that the films have a textured BCC Fe [110]/FCC NiFe [111] stacking. Saturation magnetic flux density (B/sub s/) is the average of bulk Fe and NiFe values. Coercive field (H/sub c/) value and relative permeability ( mu ) depend on the thicknesses of both Fe and NiFe layers. Saturation magnetostriction constant ( lambda s) behavior is explained as the average of lambda s values for Fe, NiFe, and Fe-NiFe interdiffusion layers. In Fe/NiFe films with 8 approximately 16-nm, superlattice modulation wavelength and around 50% Fe-layer thickness ratio, large 15-kG B/sub s/ value, 3000- mu values, and very small lambda s values less than 5*10/sup -7/ were achieved. The soft magnetic properties and the superlattice periodicity are stable at up to 200 degrees C annealing temperature. Effective interdiffusivity values are 1.9*10/sup -24/ approximately 1.5*10/sup -21/ m/sup 2/ s/sup -1/ in the 200 approximately 400 degrees C temperature range, and are found to have an Arrhenius temperature dependence. Activation energy for the interdiffusion is estimated to be 0.84 eV. Extrapolating the effective interdiffusivity value to lower temperature, Fe/NiFe films appear rather stable at an operating temperature for hard disk drives. >