Different Dynamic and Static Magnetic Anisotropy in Thin Permalloy Films
Radek Lopusnik, John P. Nibarger, Thomas J. Silva, Zbigniew J. Celinski
The values of uniaxial anisotropy Hk in thin polycrystalline Permalloy films measured by static and dynamic methods differ by as much as a factor 1.5. The anisotropy obtained with a pulsed inductive microwave magnetometer in 2.5-100 nm thick Permalloy films exhibits an additional isotropic component of 120-240 A/m not observed in static measurements. The static anisotropy value was obtained with an inductive magnetic hysteresis loop tracer. The time-resolved precessional response was measured as a function of in-plane magnetic applied bias field and the angle between the easy-axis and the applied bias field. We interpret the constant offset field as a transient component of the magnetic anisotropy that affects only dynamical response at time scales below 10 ns.