  It has been shown that the spin Hall effect from heavy transition metals can
generate sufficient spin-orbit torque and further produce current-induced
magnetization switching in the adjacent ferromagnetic layer. However, if the
ferromagnetic layer has in-plane magnetic anisotropy, probing such switching
phenomenon typically relies on tunneling magnetoresistance measurement of
nano-sized magnetic tunnel junctions, differential planar Hall voltage
measurement, or Kerr imaging approaches. We show that in magnetic
heterostructures with spin Hall metals, there exist current-induced in-plane
spin Hall effective fields and unidirectional magnetoresistance that will
modify their anisotropic magnetoresistance behavior. We also demonstrate that
by analyzing the response of anisotropic magnetoresistance under such
influences, one can directly and electrically probe magnetization switching
driven by the spin-orbit torque, even in micron-sized devices. This pump-probe
method allows for efficient and direct determination of key parameters from
spin-orbit torque switching events without lengthy device fabrication
processes.
