Anomalous anisotropic magnetoresistance effects in graphene

We investigate the effect of external stimulus (temperature, magnetic field, and gases adsorptions) on anisotropic magnetoresistance (AMR) in multilayer graphene. The graphene sample shows superlinear magnetoresistance when magnetic field is perpendicular to the plane of graphene. A non-saturated AMR with a value of −33% is found at 10 K under a magnetic field of 7 T. It is surprisingly to observe that a two-fold symmetric AMR at high temperature is changed into a one-fold one at low temperature for a sample with an irregular shape. The anomalous AMR behaviors may be understood by considering the anisotropic scattering of carriers from two asymmetric edges and the boundaries of V+(V-) electrodes which serve as active adsorption sites for gas molecules at low temperature. Our results indicate that AMR in graphene can be optimized by tuning the adsorptions, sample shape and electrode distribution in the future application.