  Current-induced spin torques are of great interest to manipulate the
orientation of nanomagnets without applying external magnetic fields. They find
direct application in non-volatile data storage and logic devices, and provide
insight into fundamental processes related to the interdependence between
charge and spin transport. Recent demonstrations of magnetization switching
induced by in-plane current injection in ferromagnetic heterostructures have
drawn attention to a class of spin torques based on orbital-to-spin momentum
transfer, which is alternative to pure spin transfer torque (STT) between
noncollinear magnetic layers and amenable to more diversified device functions.
Due to the limited number of studies, however, there is still no consensus on
the symmetry, magnitude, and origin of spin-orbit torques (SOTs). Here we
report on the quantitative vector measurement of SOTs in Pt/Co/AlO trilayers
using harmonic analysis of the anomalous and planar Hall effects as a function
of the applied current and magnetization direction. We provide an all-purpose
scheme to measure the amplitude and direction of SOTs for any arbitrary
orientation of the magnetization, including corrections due to the interplay of
Hall and thermoelectric effects. Based on general space and time inversion
symmetry arguments, we show that asymmetric heterostructures allow for two
different SOTs having odd and even behavior with respect to magnetization
reversal. Our results reveal a scenario that goes beyond established models of
the Rashba and spin Hall contributions to SOTs. The even SOT is STT-like but
stronger than expected from the spin Hall effect in Pt. The odd SOT is composed
of a constant field-like term and an additional component, which is strongly
anisotropic and does not correspond to a simple Rashba field.
