Figure 3. Spin transport and precession measurements at room temperature with spin filtering in Co|h-BN|Gr contact.

(a) Nonlocal spin valve signal (V_NL) measured at 300 K using an injection current of I = 10 μA with in-plane magnetic field. Magnetic field sweep directions are indicated by red (up) and blue (down) colors. (b) Nonlocal Hanle spin-precession signal measured as a function of the perpendicular magnetic field with I = 10 μA at 300 K, keeping the magnetization of the ferromagnetic electrodes in an in-plane parallel () and anti-parallel () configuration. The solid line is the Hanle fit (Eq. 1) to the data points using Eq. 1 for a field T. The nonlocal resistance is defined as and −. Insets in a and b show the spin valve and Hanle measurement configurations on graphene for a device with spin injection contact of a thicker layer of h-BN and detection under a thinner h-BN with Co electrodes. (c) Dependence of and spin polarization on the injection bias current at 300 K, P_i and P_d are injector and detector polarizations respectively. Inset: Dependence of P on the injection bias voltage at 300 K. The circles are the data points and the lines are guides to the eye. (d) Absolute value of the spin polarization versus the tunnel contact resistance for different devices, R_i and R_d are injector and detector resistances. The sign of the spin polarization for the R_id involving high resistance h-BN contact is negative, whereas it is positive for lower resistance devices. R_id = 65 kΩ μm² corresponds to devices with R_i = 170 kΩ μm² and R_d = 25 kΩ μm², R_id ≈ 25 kΩ μm²corresponds to a device with R_i ≈ R_d ≈ 25 kΩ. The spin polarization becomes negative when R_i increased from 25–170 kΩ μm²due to an effective increase in h-BN thickness.