Non-local spin transport devices with a tunable channel*

The spin lifetime in GaAs is known to vary strongly with carrier density near the metal to insulator transition [1]. However, a detailed study to optimize this lifetime is complicated because many replica samples need to be made and measured. This difficulty can be circumvented by employing Si:Al$_{0.3}$Ga$_{0.7}$As, a persistent photoconductor, as the spin transport medium. This material, which is structurally similar to GaAs, has been characterized and shown to have an effective carrier density which can be tuned \textit{in situ} via photo-excitation from 10$^{14}$ to 10$^{18}$ cm$^{-3 }$[2]. Heterostructures (2-$\mu $m Si:Al$_{0.3}$Ga$_{0.7}$As, a thin epitxial Fe layer, and a GaAs graded junction to create linear contacts between them) have been grown by MBE and non-local spin devices have been patterned by photolithography and wet etching. Magnetic measurements on Fe micro-patterns demonstrated the possibility of controlling the coercivity of the Fe electrodes [3]. Electrical characterization of the devices will be presented. [1] J. Kikkawa et al., Phys. Rev. Lett. 80, 4313 (1998) [2] J. Misuraca et al., Phys. Rev. B. 82, 125202 (2010) [3] K. K. Meng et al., Appl. Phys. Lett. 97, 072503 (2010).