  Spin polarized currents are employed to efficiently manipulate the
magnetization of ferromagnetic ultrathin films by exerting a torque on it. If
the spin currents are generated by means of the spin-orbit interaction between
a ferromagnetic and a non-magnetic layer, the effect is known as spin-orbit
torque (SOT), and is quantified by measuring the effective fields produced by a
charge current injected into the device. In this work, we present a new
experimental technique to quantify directly the SOT based on the measurement of
non-linearities of the dc current-voltage (IV) characteristics in Hall bar
devices employing a simple instrumentation. Through the analysis of the IV
curves, the technique provides directly the linearity of the effective fields
with current, the detection of the current range in which the thermal effects
can be relevant, the appearance of misalignments artefacts when the symmetry
relations of SOT are not fulfilled, and the conditions for the validity of the
single domain approximations, which are not considered in switching current and
second harmonic generation state-of-the-art experiments. We have studied the
SOT induced antidamping and field-like torques in Ta/Co/Pt asymmetric stacks
with perpendicular magnetic anisotropy.
