Giant Magnetoresistance in Organic Spin Valves

Interfacial diffusion between magnetic electrodes and organic spacer layers is a serious problem in the organic spintronics which complicates attempts to understand the spin-dependent transport mechanism and hurts the achievement of a desirably high magnetoresistance (MR). We deposit nanodots instead of atoms onto the organic layer using buffer layer assist growth. Spin valves using this method exhibit a sharper interface and a giant MR of up to $\sim 300\%$. Analysis of the current-voltage characteristics indicates that the spin-dependent carrier injection correlates with the observed MR.

Figure 1

(a) Schematic diagrams of a BLAG spin valve and a conventional spin valve. Cross-sectional schematic diagram of the conventional device (b) indicates the short circuit area (sketched by solid white line) due to the diffusion of Co atoms. For the BLAG device (c), several layers of Co nanodots (average nanodot volume $\sim 3.3{\mathrm{nm}}^3$) are formed using BLAG prior to the deposition of top electrodes which effectively minimizes the interdiffusion process.

Figure 2

Comparison of the MR loop response for junctions with a lower effective ${\mathrm{Alq}}_3$ thickness prepared by BLAG (a),(c) and conventional methods (b),(d), at a bias current of $-3\mu \mathrm{A}$. (e) MR loop of the effective ${\mathrm{Alq}}_3$ thickness (93 nm) for BLAG junctions at a bias voltage of $-0.5\mathrm{V}$ shows giant MR response (inset: the MR loop of a conventional junction at the same effective thickness and bias voltage). The measurements were all taken at 10 K.

Figure 3

Bias voltage dependence of MR ratio measured at 10 K comparison of conventional junctions and BLAG junctions with different ${\mathrm{Alq}}_3$ effective thicknesses: 23 nm (a), 67 nm (b), and 93 nm (c). (d) MR measured as a function of effective thickness for the two types of junctions.

Figure 4

Current density-voltage ($J\mathrm{\text{−}}V$) and ($dI/dV)$ characteristics for the BLAG junction with effective thickness ${\mathrm{Alq}}_3$ spacer layers of 23 nm (a), 67 nm (b), and 93 nm (c) in antiparallel and parallel configurations. Experimental data for 93 nm junction at both antiparallel configuration ($-40\mathrm{Oe}$) and parallel configuration ($-190\mathrm{Oe}$) are fitted using Eq. (1) (solid lines).