  We predict that the spin-transfer, $T_{i,||}$, and field-like, $T_{i,\bot}$,
components of the {\it local} spin torque are dramatically enhanced in
double-barrier magnetic tunnel junctions. The {\it spin-mixing} enhancement is
due to the energetic proximity of majority and minority quantum well states
(QWS) of different quantum numbers within the bias window. $T_{i,||}$ exhibits
a switch-on and switch-off step-like bias behavior when spin polarized QWS
enter the bias window or exit the energy band, while $T_{i,\bot}$, changes sign
between switch-on biases. The {\it net} $T_{\bot}$ exhibits an anomalous
angular behavior due to the bias interplay of the bilinear and biquadratic
effective exchange couplings.
