Gate-tunable large magnetoresistance in semiconductor-based spin valve devices (Conference Presentation)

A spin-dependent and electric-field tunable magnetoresistance (MR) of a semiconducting (SC) channel placed between two ferromagnetic (FM) contacts is a key ingredient in many novel spin-based device concepts. Whereas successful realization of such devices requires a large magnetoresistance signal, the signals measured in semiconductor-based devices are usually very low, well below 1\%, because of highly resistive tunnel FM/SC interfaces. In this talk, we will discuss how the finite electric fields effects in lateral FM/SC/FM devices lead to enhancement of the measured magnetoresistance by increasing the efficiency of the spin transport in the channel and boosting spin-to-charge conversion at the FM/SC interface. We will illustrate this discussion with the results of our recent experiments on lateral all-semiconductor spin valve devices with a transport channel formed in the two-dimensional electron system embedded in GaAs/(Al,Ga)As interface and with ferromagnetic (Ga,Mn)As/GaAs Esaki diodes as source and drain contacts [1]. We have measured very large two-terminal spin valve signals, in order of 1 kOhm in such devices, with MR reaching even up to 80\% in the nonlinear regime of the current-voltage characteristic [2]. We will also demonstrate that the MR signal can be additionally tuned by means of an electric gate, with the gating scheme based on switching between uni- and bidirectional spin diffusion, without resorting to spin–orbit coupling. The work has been supported by Deutsche Forschungsgemeinschaft (DFG) through SFB689.