Optimized Device Characteristics of Lateral Spin Valves

The lateral spin valve is a planar ferromagnet/nonmagnet/ferromagnet $(F \hbox{1}/N/F\hbox{2})$ structure with a resistance modulation $ \Delta R$ that derives from a nonequilibrium population of spin-polarized conduction electrons. This paper analyzes the characteristics of a future-generation all-metal device fabricated with minimum feature size $f$ of 50 nm. Theoretical principles of operation are reviewed, and the “inverse scaling” rule is derived: Output resistance modulation varies inversely with the volume of the nonmagnetic material in the device. The thermodynamic formalism of Johnson and Silsbee is also used to study details of charge and spin transport at the $F/N$ interface and to understand the limits of the fractional polarization of injected current. Experiments on lateral spin valves with $N$ channels having widths of 150 nm are described. A high fractional polarization is observed for structures with low interface resistance. A survey of recent results on similar devices shows that inverse scaling is upheld over ten decades of sample volume. Using these experimentally observed parameters and extrapolating further to $f = \hbox{50}\ \hbox{nm}$ , a spin-accumulation device that is fabricated to have an output impedance of 50 $\Omega$ and an output modulation of 50 $\Omega\ (\Delta R/R = \hbox{100}\%)$ is discussed.