Ferroelectric spintronics

Classical spintronics uses the exchange interaction in ferromagnets to induce the spin-polarization of charge currents. Another effect, the spin-orbit coupling, is also able to create spin currents from charge currents, in non-ferromagnetic materials. This spin to charge interconversion can be obtained either through the spin Hall effect in bulk materials, or using the Edelstein-Rashba effect at interfaces.



This new mean of controlling spins has led to the emergence in the last 15 years of a new field of research, spinorbitronics. On one hand, the charge to spin conversion allows to create torques acting on the magnetization, inducing magnetization switching for memory applications, or magnetization oscillations for rf applications. On the other hand, the spin to charge conversion can be used to develop post-CMOS logic devices with in-memory capability, such as the MESO device proposed by Intel [1].



In this context, we recently demonstrated that the spin-to-charge interconversion, due to the spin-orbit coupling, can be controlled in sign in a non-volatile way, using either ferroelectricity or charge trapping effects [2,3], in particular in oxide 2D electron gases (2DEGs).



Concerning the charge-to-spin conversion, we report here the non-volatile electric-control of spin-orbit torques, with two electrical remanent states, in a perpendicular ferromagnet-SrTiO₃ system. The remanent electric-control of the efficiency is demonstrated using second harmonic Hall methods, with a sign inversion of the anti-damping-like effective field. These results are consistent with a combination of both an intrinsic modulation of the efficiency and an extrinsic modulation due to the non-volatile electric-control of the current injection in the 2DEG.



Concerning the spin-to-charge conversion, we show using spin-pumping experiments that it can be controlled in sign in a remanent way, through the ferroelectric polarization. We propose a new logic device based on this effect, the FESO (for FerroElectric Spin-Orbit) device, with the aim of lowering the power consumption of information and communication technology devices.