Abstract
We report on measurements of the easy-plane anisotropy field of MgO-based magnetic tunnel junctions. The free layer easy-plane anisotropy field was measured by perpendicular field thermal noise-based ferromagnetic resonance spectroscopy (T-FMR) and by tunneling magnetoresistance (TMR). A model was derived to extract the saturation field of the free layer from perpendicular TMR-based resistance-field data. Both measurements confirm that for 20 Å CoFeB free layers, the measured effective easy-plane anisotropy field of 4πMeff equal to (5.3±0.6) kOe is well below the bulk value based on demagnetization. T-FMR measurements show a base resonant mode with a linear field dependence in accordance with the Kittel formula. Higher-order modes are also observed, suggesting the presence of confined spin-wave excitations. The mode frequency spacing, however, shows significant device-to-device variations whose origin is not yet uniquely determined.
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