Hysteresis loops of magnetoconductance in graphene devices

We report very low-temperature magnetoconductance Delta G measurements on graphene devices with the magnetic field H applied parallel to the carbon sheet. The Delta G(H) signal depends on the gate voltage V(g) and its sign is related to the universal conductance fluctuations. When the magnetic field is swept at fast rates, Delta G displays hysteresis loops evident for different sizes and at different transport regimes of the devices. We attribute this to the magnetization reversal of paramagnetic centers in the graphene layer, which might originate from defects in our devices.