  A clear gate voltage tunable weak antilocalization and a giant
magnetoresistance of 400 percent are observed at 1.9 K in single layer graphene
with an out-of-plane field. A large magnetoresistance value of 275 percent is
obtained even at room temperature implying potential applications of graphene
in magnetic sensors. Both the weak antilocalization and giant magnetoresistance
persists far away from the charge neutrality point in contrast to previous
reports, and both effects are originated from charged impurities.
Interestingly, the signatures of Shubnikov-de Haas oscillations and the quantum
Hall effect are also observed for the same sample.
