Frequency-dependent complex permeability in Zr-substituted permalloy thin films

In this work, we investigate Zr substitution in Permalloy Ni₈₀Fe₂₀ thin films in order to control the magnetic properties and then to tune the resonance frequency at lower values with high permeability levels. The structural transition from a crystalline to an amorphous phase, saturation induction, in-plane anisotropy, electrical resistivity, and frequency-dependent permeability are studied for the Zr content ranging from 0 to 17% at. The high-frequency permeability of these (Ni₈₀Fe₂₀)_1-xZr_x films is first measured in the 0.1-3-GHz range using a permeameter. Assuming a gyroresonance mechanism, the frequency-dependence of the permeability is studied as a function of the magnetization, anisotropy field, and damping parameter deduced from ferromagnetic resonance characterizations. For a Zr concentration of 17%, a resistivity of 260 μΩ·cm is obtained as well as very soft properties (H_c<0.5 Oe). We also show that the permeability is drastically affected by the Zr substitution with a significant shift of the resonance frequency from 600 to 300 MHz, which correlates with the decrease of the saturation induction and a very low anisotropy.