Annealing temperature dependence of microwave permeability in CoFe/MnIr bilayers

Abstract

We measured microwave permeability in thermal annealed CoFe/MnIr bilayers. The ferromagnetic resonance frequency (f FMR ) and Gilbert damping constant (α G ) are analyzed using the Landau-Lifshitz-Gilbert equation. The f FMR increases with the exchange bias field, and it can be easily tuned over 10 GHz either by controlling the CoFe thickness or through modifications of unidirectional anisotropy by thermal annealing. The extracted α G is inversely proportional to the exchange bias field, and this behavior is caused by the suppression of the anisotropy field distribution due to an increase in the exchange bias field. Thus, low loss performance in microwave frequency range can be achieved in exchange biased CoFe/MnIr bilayers.

Intrinsic and extrinsic Gilbert damping in exchange-biased IrMn/Cu/CoFe trilayer films

“…Inverse relationships (H app ≃ 300 Oe) between α and H eb have also been observed. 13,14) Several results even indicate that α does not have any significant relationship with H eb (H app ≃ 50 Oe). 15,16) All these works measured α under a low external magnetic field where additional spin scattering due to inhomogeneity in the specimen could be present.…”