Magnetic hysteresis dynamics in Ni₈₀Fe₂₀ thin films

The dynamic magnetization reversal behavior of polycrystalline Ni₈₀Fe₂₀ films (thickness 60 and 200 Å) was studied in the temperature range 90 ∼ 300 K by applying a magnetic field along the easy magnetization axis of the samples. The loop area A is found to follow the scaling relation A ∝ H^α₀Ω^βT^-γ with α ≈ 0.9, β ≈ 0.8, and γ = 0.38 for both thicknesses, where H₀ is the magnetic field amplitude, Ω is frequency, and T is temperature. This behavior is only qualitatively consistent with theoretical models if the magnetization reversal mechanism is identical for both films, independently of the applied field and sample temperature. The exponents α and βare found to be independent of the temperature, indicating that the dynamic reversal mechanism is unchanged in this temperature range. The hard-axis loop also evolves with increasing frequency, and the loop areas of the hard axis obey the scaling relation with β_HA = 0.47 ± 0.02.