We study fully hexagonal boron nitride (hBN) encapsulated graphene spin valve devices at room temperature. The device consists of a graphene channel encapsulated between two crystalline hBN flakes: thick-hBN flake as a bottom gate dielectric substrate which masks the charge impurities from ${\mathrm{SiO}}_2/\mathrm{Si}$ substrate and single-layer thin-hBN flake as a tunnel barrier. Full encapsulation prevents the graphene from coming in contact with any polymer/chemical during the lithography and thus gives homogeneous charge and spin transport properties across different regions of the encapsulated graphene. Further, even with the multiple electrodes in-between the injection and the detection electrodes which are in conductivity mismatch regime, we observe spin transport over $12.5-\mu \mathrm{m}$-long distance under the thin-hBN encapsulated graphene channel, demonstrating the clean interface and the pinhole-free nature of the thin hBN as an efficient tunnel barrier.

• Received 14 January 2016
• Revised 29 February 2016

DOI:https://doi.org/10.1103/PhysRevB.93.115441