Spin-wave FMR in annealed NiFe/FeMn thin films

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Abstract
Ferromagnetic resonance (FMR) investigations have been made at 33 GHz on as-deposited and on annealed bilayer NiFe/FeMn thin films. Supplemental investigations were made at 9 GHz. Following a 350 °C anneal, for 1 h or longer in duration, the NiFe FMR spectrum was found to be characterized by a sequence of spin-wave resonance (SWR) modes. The behavior of the SWR modes is in accord with the presence of a thin ferromagnetic layer at the NiFe/FeMn interface with magnetization different from the bulk. Transmission electron microscopy (TEM) examinations indicate that annealing promotes formation of an interdiffused layer at the NiFe/FeMn interface and favors NiFe grain growth. Magnetic field limitations precluded FMR at 0° (perpendicular) field orientation. At various field orientations below the critical angle, the resonant fields, Hn, were found to vary with mode number n as n2. Also, for n>1, the FMR-SWR linewidth ΔHn has a component varying as n2. From the 33-GHz 16° orientation data, the exchange constant A is computed to be (1.03±0.15)×10−6 erg/cm. The application of an in-plane magnetic field during anneal produces a reduction of the SWR mode intensities and a broadening of the principal peak. A perpendicular magnetic field had little effect.

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