  Unidirectional magnetoresistance (UMR) in a ferromagnetic bilayer due to the
spin Hall effects (SHEs) provides a facile means of probing in-plane
magnetization to avoid complex magnetic tunnel junctions. However, the UMR
signal is very weak and usually requires a lock-in amplifier for detection even
in the bilayer involving Ta or Pt with a large spin Hall angle (SHA). Here we
report a type of UMR, termed as the anomalous UMR (AUMR), in a single CoFeB
layer without any adjacent SHE layers, where the UMR signal is about 10 times
larger than that in Ta/CoFeB structures and can be detected by using
conventional dc multimeters in the absence of lock-in amplifiers. We further
demonstrate that the extracted AUMR by excluding thermal contributions shows
reversal signs for the CoFeB and NiFe single layers with opposite SHAs,
indicating that the AUMR may originate from the self-generated spin
accumulation interacting with magnetization through the giant
magnetoresistance-like mechanism. These results suggest that the AUMR
contributes UMR signals larger than the interfacial spin Hall UMR in the
CoFeB-involved systems, providing a convenient and reliable approach to detect
in-plane magnetization for the two-terminal spintronic devices.
