(A) study on sign inversion of spin hall magnetoresistance in non-magnet/NiFe bilayer

Abstract

Spin Hall magnetoresistance (SMR) in heavy metal (HM)/ferromagnet (FM) bilayer structures results from the interaction between spin Hall effect-induced spin currents in the HM and magnetic moment of the FM. The resistance of the HM/FM bilayers is determined by the relative orientations of the induced spins and the mag-netization

it is lowest when they are parallel aligned. In this work, we report the sign inversion of the SMR in HM/NiFe bilayers as a function of NiFe thickness, where HM is Ta or Pt. For a thin NiFe layer, normal or posi-tive SMR is observed

however, with an increasing NiFe thickness, the sign of the SMR is inverted. This is at-tributed to a negative SMR in the NiFe layer and its dominant contribution to the SMR in the bilayer with a thicker NiFe. We also observe a similar NiFe thickness dependence of anomalous Hall resistance of the bilayers, which is the variation of the transverse resistance arising from the SMR. The sign inversion of SMR in HM/NiFe bilayer cannot be explained by the conventional SMR model, which requires further theoretical and experi-mental investigation.