  We observe both dc voltage rectification and frequency conversion that occur
when a reference microwave current is injected to a MgO based magnetic tunnel
junction (MTJ). The rectification that is spin-transfer torque dependent is
observed when the frequency of the input microwave current coincides with the
resonance frequency of the magnetization of the active layer. In addition, we
demonstrate that frequency conversion is the result of amplitude modulation
between the reference signal and the resistance of the MTJ that is fluctuating
at the resonance frequency of the magnetization of the active layer.
