Spin-orbit coupling effects in materials with broken inversion symmetry are responsible for peculiar spin textures. Among them, ferroelectric materials allow for non-volatile control of the spin degree of freedom through the non-volatile electrical inversion of the spin texture, through to their reversible spontaneous polarization. Such functionality holds potential for technological applications exploiting spin effects controlled by electric fields. The ferroelectric Rashba semiconductor Germanium Telluride stands out as material for Spin-Orbitronics: its ferroelectricity provides a nonvolatile state variable able to generate and drive a giant bulk Rashba-type spin splitting of the electronic bands, while its semiconductivity would allow for the realization of spin-based transistors. The ferroelectric control of the bands topology and of the spin texture is expected to reflect in the tunability of the spin transport properties. Here we exploit the unidirectional spin Hall magnetoresistance of Fe/GeTe heterostructures to characterize charge-to-spin conversion in GeTe. Our preliminary results indicate a sizable conversion efficiency at low temperature (120 K), which promotes ferroelectric Rashba semiconductors as promising candidates for the implementation of non-volatile electrically reconfigurable computing devices based on spin transport in semiconductors.
Toward the design of large-scale electronic circuits that are entirely spintronics-driven, organic semiconductors
have been identified as a promising medium to transport information using the electron spin. This requires a
ferromagnetic metal-organic interface that is highly spin-polarized at and beyond room temperature, but this key building
block is still lacking. We show how the interface between Co and phthalocyanine molecules constitutes a promising
candidate. In fact, spin-polarized direct and inverse photoemission experiments reveal a high degree of spin polarization
at room temperature at this interface.
We report on the measurements of spin diffusion length and lifetime in Germanium with both magneto-electro-optical
and magneto-electrical techniques. Magneto-electro-optical measurements were made by optically inject in Fe/MgO/Ge
spin-photodiodes a spin polarized population around the Γ point of the Brillouin zone of Ge at different photon energies.
The spin diffusion length is obtained by fitting by a mathematical model the photon energy dependence of the spin
signal, due to switching of the light polarization from left to right, leading to a spin diffusion length of 0.9±0.2 μm at
room temperature. Non-local four-terminals and Hanle measurements performed on Fe/MgO/Ge lateral devices, at room
temperature, instead lead to 1.2±0.2 μm. The compatibility of these values among the different measurement methods
validates the use all of all of them to determine the spin diffusion length in semiconductors. While electrical methods are
well known in semiconductor spintronics, in this work we demonstrate that the optical pumping versus photon energy is
an alternative and reliable method for the determination of the spin diffusion length whereas the band structure of the
semiconductor allows for a non-negligible optical spin orientation.
We report on spin-photodiodes based on fully epitaxial Fe/MgO/Ge(001) heterostructures for room temperature
integrated detection of light helicity at 1300 nm and 1550 nm wavelengths. The degree of circular polarization of
light determines the spin direction of photo-carriers in Ge that are filtered by the Fe/MgO analyzer. Spin-detection
experiments are performed by measuring the photocurrent while illuminating the spin-photodiodes with left or right
circularly polarized light, under the application of a magnetic field parallel to the light direction which drives the Fe
magnetization out of plane. We found that the spin-photodiodes spin filtering asymmetry is reduced by ∼40% in
forward bias and by less than 15% in reverse bias, when increasing the photon wavelength from 1300 nm to
1550 nm. This result, apparently counterintuitive because of the larger spin polarization of the photo-carriers
generated at 1550 nm with respect to that at 1300 nm, is explained in terms of the different spatial profile of carrier
generation inside Ge. The larger penetration depth of light at 1550 nm leads to a smaller polarization of photocarriers
when they reach the MgO tunneling barrier, due to the more efficient spin relaxation during transport.