Measurement of Effective Free Layer Magnetization Orientation of TMR Sensors

Measurements of thermal magnetization fluctuation noise spectrum in multi-directional magnetic field reveal tilt of effective free layer orientation in TMR sensors. We propose a method for effective sensor stiffness field measurement and demonstrate that deviations of stiffness from nominal values are caused by the angular dependence of the stiffness field. Ferro-magnetic resonance peak measurements indicate that the free layer magnetization orientation may be tilted from the cross-track direction. This magnetization tilt is caused by reference layer, hard bias problems and shape anisotropy effects. This reduces sensor efficiency and leads to amplitude asymmetry, multi-domain configuration and sensor instability. FMR-based method for detection of potentially unstable heads based on these observations is proposed.