  The broadband ferromagnetic resonance (FMR) linewidth of the free layer of
magnetic tunnel junctions is used as a simple diagnostic of the quality of the
magnetic structure. The FMR linewidth increases near the field regions of free
layer reversal and pinned layer reversal, and this increase correlates with an
increase in magnetic hysteresis in unpatterned films, low frequency noise in
patterned devices, and previous observations of magnetic domain ripple by use
of Lorentz microscopy. Postannealing changes the free layer FMR linewidth
indicating that considerable magnetic disorder, originating in the
exchange-biased pinned layer, is transferred to the free layer.
