An experimental technique has been developed to characterize spin-transfer driven magnetization dynamics. It was tested on a nanopillar spin valve with perpendicular anisotropy by measuring the nanopillar voltage under ac injected current ͑dV / dI͒, and ac magnetic field ͑dV / dH͒. Both the amplitude and the sign of the signals are different which reveals the different influences of the current and the field on the magnetization dynamics. Comparison between experiments and macrospin simulation shows that dV / dH measurements reveal the presence of a " canted state " demonstrating that dV / dH and dV / dI measurements are complementary techniques to probe magnetic states and their dynamics. It is now well established that magnetization switching or precession can be induced by spin polarized injected current due to the spin transfer torque ͑STT͒ effect. 1,2 This topic has been extensively studied because of the interesting physics and the potential applications for spin transfer magnetic random access memories and high-frequency oscillators.