ABSTRACT
We show spin lifetimes of 12.6 ns and spin diffusion lengths as long as 30.5 µm in single layer graphene nonlocal spin transport devices at room temperature. This is accomplished by the fabrication of Co/MgO-electrodes on a Si/SiO2 substrate and the subsequent dry transfer of a graphene-hBN-stack on top of this electrode structure where a large hBN flake is needed in order to diminish the ingress of solvents along the hBN-to-substrate interface. Interestingly, long spin lifetimes are observed despite the fact that both conductive scanning force microscopy and contact resistance measurements reveal the existence of conducting pinholes throughout the MgO spin injection/detection barriers. Compared to previous devices, we observe an enhancement of the spin lifetime in single layer graphene by a factor of 6. We demonstrate that the spin lifetime does not depend on the contact resistance area products when comparing all bottom-up devices indicating that spin absorption at the contacts is not the predominant source for spin dephasing.
ABSTRACT
We present a new fabrication method of graphene spin-valve devices that yields enhanced spin and charge transport properties by improving both the electrode-to-graphene and graphene-to-substrate interface. First, we prepare Co/MgO spin injection electrodes onto Si(++)/SiO2. Thereafter, we mechanically transfer a graphene-hBN heterostructure onto the prepatterned electrodes. We show that room temperature spin transport in single-, bi-, and trilayer graphene devices exhibit nanosecond spin lifetimes with spin diffusion lengths reaching 10 µm combined with carrier mobilities exceeding 20,000 cm(2)/(V s).
