Large local Hall effect in pin-hole dominated multigraphene spin-valves
  We report local and non-local measurements in pin-hole dominated mesoscopic multigraphene spin-valves. Local spin-valve measurements show spurious switching behavior in resistance during magnetic field sweeping similar to the signal observed due to spin-injection into multigraphene. The switching behavior has been explained in terms of local Hall effect due to thickness irregularity of the tunnel barrier. Local Hall effect appears due to large local magnetostatic field produced at the roughness in the AlO$_x$ tunnel barrier. The effect of this local Hall effect is found to reduce as temperature is increased above 75 K. The strong local Hall effect hinders spin-injection into multigraphene resulting in no spin signal in non-local measurements. 
P. K. Muduli, J. Barzola-Quiquia, S. Dusari, Ana Ballestar, F. Bern,   W. Bohlmann, P. Esquinazi
cond-mat.mes-hall