The spin Hall effect in ferromagnets is of great interest in the field of spintronics, and while the effect has been quantified in many materials, the dependence of the spin Hall angle on the relative orientation of spin polarization and the magnetization is less well studied. Of equal importance for the purpose of spin-charge interconversion in ferromagnets is the spin relaxation length, which is predicted to be highly anisotropic with respect to magnetization. Using a modified lateral spin valve geometry with a copper channel and permalloy spin injector, we measure the dependence of the spin Hall angle and spin relaxation length on magnetization orientation in permalloy and nickel, using two distinct device geometries. This allows us to disentangle the contributions of the spin relaxation length and spin Hall angle to the measured spin-charge interconversion voltage output. Our results indicate a large anisotropy in both the spin relaxation length and spin Hall angle in both permalloy and nickel, in agreement with theoretical calculations. The quantities change in opposite directions, with the spin relaxation length rising as the magnetization is moved parallel to the spin polarization and the spin Hall angle falling, leading to a near total cancellation of the spin-charge interconversion output.

Two-dimensional electron gases (2DEGs) in quantum paraelectric SrTiO3 (STO) exhibit high electron mobilities at low temperature, superconductivity, and efficient spin-charge interconversion owing to their Rashba spin-orbit coupling. However, such 2DEGs have almost exclusively been generated in STO single crystals, and few attempts to replace crystals by heteroepitaxial STO films have mostly resulted in low mobilities, limiting device integration and functional tuning such as strain-induced ferroelectricity. Here, we use hybrid oxide molecular beam epitaxy to grow high-quality strain-engineered STO films that are ferroelectric up to 165 K. By sputtering thin aluminum layers at room temperature, we generate a 2DEG at their surface. Raman spectroscopy and magnetotransport measurements indicate that the ferroelectric character is retained after 2DEG formation. These results suggest that our samples behave as ferroelectric 2DEGs up to temperatures well above previous results based on Ca-STO substrates (∼30 K), opening the way toward thin-film-based ferroelectric 2DEGs operating at room temperature.

We report a new approach to generate and detect spin currents by exploiting the interplay between spin-orbit effects and ferroelectricity, in two classes of materials: two-Dimensional Electron Gases (2DEGS) appearing at oxides surfaces or interfaces [1], and ferroelectric Rashba semiconductors [2]. While spintronics has traditionally relied on ferromagnetic metals as spin generators and detectors, efficient spin-charge interconversion enabled by spin-orbit coupling in non-magnetic systems has drawn considerable interest in recent years, in a new field called spinorbitronics.Our results demonstrate that the spin-to-charge conversion, due to the spin-orbit coupling, can be controlled in sign in a remanent way, through the ferroelectric polarization. Such a control can lead to the emergence of a ferroelectric spintronics, which could result in a large reduction of the power consumption of non-volatile spintronic devices. It also provides a way for a non-destructive readout of ferroelectric states.

The Magnetoelectric Spin-Orbit (MESO) technology aims to bring logic into memory by combining a ferromagnet with a magnetoelectric (ME) element for information writing, and a spin-orbit (SO) element for information read-out through spin-charge conversion. Among candidate SO materials to achieve a large MESO output signal, oxide Rashba two-dimensional electron gases (2DEGs) have shown very large spin-charge conversion efficiencies, albeit mostly in spin-pumping experiments. Here, all-electrical spin-injection and spin-charge conversion experiments in nanoscale devices harnessing the inverse Edelstein effect of SrTiO3 2DEGs are reported. Nanodevices aredesigned, patterned, and fabricated in which a spin current injected from a cobalt layer into the 2DEG is converted into a charge current. The spin-charge conversion signal is optimized by applying back-gate voltages and studied its temperature evolution. It further disentangles the inverse Edelstein contribution from spurious effects such as the planar Hall effect, the anomalous Hall effect, or the anisotropic magnetoresistance. The combination of non-volatility and high energy efficiency of these devices can potentially lead to new technology paradigms for beyond-CMOS computing architectures.

The linear magnetoelectric effect (ME) is the phenomenon by which an electric field produces a magnetization. Its observation requires both time-reversal and space-inversion symmetries to be broken, as in multiferroics. While the ME effect has only been studied in insulating materials, it can actually exist in non-centrosymmetric conductors such as two-dimensional electron gases (2DEGs) with Rashba spin-orbit coupling. It is then coined the Edelstein effect (EE), by which a bias voltage -- generating a charge current -- produces a transverse spin density, i.e. a magnetization. Interestingly, 2D systems are sensitive to voltage gating, which provides an extra handle to control the EE. Here, we show that the sign of the EE in a SrTiO$_3$ 2DEG can be controlled by a gate voltage. We propose various logic devices harnessing the dual control of the spin density by current and gate voltages and discuss the potential of our findings for gate-tunable non-reciprocal electronics.

We report on the structural, electric and magnetic properties of (NixCo1−x)B ferromagnetic nanotubes, displaying azimuthal magnetization. The tubes are fabricated using electroless plating in polycarbonate porous templates, with lengths of several tens of micrometers, diameters from 100 nm to 500 nm and wall thicknesses from 10 nm to 80 nm. The resistivity is ∼1.5×10−6Ω m, and the anisotropic magnetoresistance (AMR) of 0.2 to 0.3%, one order of magnitude larger (resp. smaller) than in the bulk material, which we attribute to the resistance at grain boundaries. We determined the azimuthal anisotropy field from M(H) AMR loops of single tubes contacted electrically. Its magnitude is around 10 mT, and tends to increase with the tube wall thickness, as well as the Co content. However, surprisingly it does not dependent much on the diameter nor on the curvature.

Spin-orbit torques (SOTs) have opened a novel way to manipulate the magnetization using in-plane current, with a great potential for the development of fast and low power information technologies. It has been recently shown that two-dimensional electron gases (2DEGs) appearing at oxide interfaces provide a highly efficient spin-to-charge current interconversion. The ability to manipulate 2DEGs using gate voltages could offer a degree of freedom lacking in the classical ferromagnetic/spin Hall effect bilayers for spin-orbitronics, in which the sign and amplitude of SOTs at a given current are fixed by the stack structure. Here, we report the non-volatile electric-field control of SOTs in an oxide-based Rashba-Edelstein 2DEG. We demonstrate that the 2DEG is controlled using a back-gate electric-field, providing two remanent and switchable states, with a large resistance contrast of 1064%. The SOTs can then be controlled electrically in a non-volatile way, both in amplitude and in sign. This achievement in a 2DEG-CoFeB/MgO heterostructures with large perpendicular magnetization further validates the compatibility of oxide 2DEGs for magnetic tunnel junction integration, paving the way to the advent of electrically reconfigurable SOT MRAMS circuits, SOT oscillators, skyrmion and domain-wall-based devices, and magnonic circuits.

Driving a spin‐logic circuit requires the production of a large output signal by spin‐charge interconversion in spin‐orbit readout devices. This should be possible by using topological insulators, which are known for their high spin‐charge interconversion efficiency. However, high‐quality topological insulators have so far only been obtained on a small scale, or with large scale deposition techniques that are not compatible with conventional industrial deposition processes. The nanopatterning and electrical spin injection into these materials have also proven difficult due to their fragile structure and low spin conductance. The fabrication of a spin‐orbit readout device from the topological insulator Sb 2 Te 3 deposited by large‐scale industrial magnetron sputtering on SiO 2 is presented. Despite a modification of the Sb 2 Te 3 layer structural properties during the device nanofabrication, a sizeable output voltage is measured that can be unambiguously ascribed to a spin‐charge interconversion process. The results pave the way for the integration of layered van der Waals materials in spin‐logic devices.

The Magnetoelectric Spin-Orbit (MESO) technology aims to bring logic into memory by combining a ferromagnet with a magnetoelectric (ME) element for information writing, and a spin-orbit (SO) element for information read-out through spin-charge conversion. Among candidate SO materials to achieve a large MESO output signal, oxide Rashba two-dimensional electron gases (2DEGs) have shown very large spin-charge conversion efficiencies, albeit mostly in spin-pumping experiments. Here, we report all-electrical spin-injection and spin-charge conversion experiments in nanoscale devices harnessing the inverse Edelstein effect of SrTiO3 2DEGs. We have designed, patterned and fabricated nanodevices in which a spin current injected from a cobalt layer into the 2DEG is converted into a charge current. We optimized the spin-charge conversion signal by applying back-gate voltages, and studied its temperature evolution. We further disentangled the inverse Edelstein contribution from spurious effects such as the planar Hall effect, the anomalous Hall effect or the anisotropic magnetoresistance. The combination of non-volatility and high energy efficiency of these devices could potentially lead to new technology paradigms for beyond-CMOS computing architectures.

The spin-dependent transport properties of paramagnetic metals are roughly invariant under rotation. By contrast, in ferromagnetic materials the magnetization breaks the rotational symmetry, and thus the spin Hall effect is expected to become anisotropic. Here, using a specific design of lateral spin valves, we measure electrically the spin Hall Effect anisotropy in NiCu and NiPd, both in their ferromagnetic and paramagnetic phases. We show that the appearance of the ferromagnetic order does not lead to a sizeable anisotropy of the spin charge interconversion in these materials.

We focus on rare-earth-free anti-perovskite Mn4−xNixN epitaxial films, which can be used for ultrafast current-induced domain wall motion (CIDWM) in magnetic strips. The magneto-transport properties of these materials are very important for a deep understanding of CIDWM. In this study, we investigated the magneto-transport properties of Mn4−xNixN epitaxial films grown on SrTiO3(001) and MgO(001) substrates through anisotropic magnetoresistance (AMR) measurements at temperatures between 2 and 300 K. In samples with a small Ni composition such as x = 0.05−0.1, the AMR ratio of Mn4−xNixN drastically decreased with increasing temperature. We also analyzed the twofold and fourfold symmetries in the AMR curves. Fourfold symmetry is caused by tetragonal crystal fields and is unique to anti-perovskite 3d-metal nitrides such as Mn4N and Fe4N. Only slight fourfold symmetry was observed in Mn4−xNixN. We also performed first-principles calculations with the Vienna ab initio simulation package (VASP) to obtain the projected density of states (PDOS) of d orbitals in Mn4−xNixN, which is responsible for the magnetism of these materials. We conclude that these results are due to the Ni atoms, which function as magnetic impurities and lead to a noticeable change in PDOS, as proved by VASP calculation.

Due to its half metallic nature, La0.7Sr0.3MnO3 is an attractive highly correlated electronic system to obtain ultralow magnetic damping. In this paper we analyze the temperature and thickness dependence of the damping of the magnetization dynamic of epitaxial thin La0.7Sr0.3MnO3 films. Our analysis reveals that the damping encompasses resistivelike and conductivelike contributions, as in transition metal ferromagnets. The data also show a large increase of the ferromagnetic resonance linewidth at low temperature, a feature that we ascribe to the presence of a dead layer, insulating and magnetically active, that behaves like a spin sink. The associated spin-pumping term shows a strong temperature dependence, linked to that of the spin mixing conductance. By clarifying some unexplored aspects of spin dynamics in half-metallic manganites, our results contribute to the progress in the burgeoning field of oxide spin orbitronics.

The ferrimagnet Mn4N forms a family of compounds useful in spintronics. In a compound comprising non-magnetic and magnetic elements, one basically expects the compound to become ferromagnetic when the proportion of the magnetic element increases. Conversely, one does not expect ferromagnetism when the proportion of the non-magnetic element increases. Surprisingly, Mn4N becomes ferromagnetic at room temperature when the Mn content is decreased by the addition of In atoms, a non-magnetic element. X-ray magnetic circular dichroism measurement reveals that the magnetic moment of Mn atoms at face-centered sites, Mn(II), reverses between x= 0.15 and 0.27 and aligns parallel to that of Mn atoms at corner sites, Mn(I), at x = 0.27 and 0.41. The sign of the anomalous Hall resistivity also changes between x = 0.15 and 0.27 in accordance with the reversal of the magnetic moment of the Mn(II) atoms. These results can be interpreted using first-principles calculations, showing that the magnetic moment of Mn(II) sites which are the nearest neighbors to the In atom align to that of Mn(I) sites.

The spin-dependent transport properties of paramagnetic metals are roughly invariant under rotation. By contrast, in ferromagnetic materials the magnetization breaks the rotational symmetry, and thus the spin Hall effect is expected to become anisotropic. Here, using a specific design of lateral spin valves, we measure electrically the spin Hall Effect anisotropy in NiCu and NiPd, both in their ferromagnetic and paramagnetic phases. We show that the appearance of the ferromagnetic order does not lead to a sizeable anisotropy of the spin charge interconversion in these materials.

This work reports remanent electric-control of spin-orbit torques (SOT) in a perpendicular ferromagnet-SrTiO3 system. Non-volatile electric-control of the sheet resistance is achieved with 1150% contrast, and two remanent resistivity states. A remanent electric-control of the SOT efficiency is demonstrated using second harmonic Hall methods, with sign inversion of the anti-damping-like effective field. These results are consistent with a combination of both intrinsic modulation of the SOT efficiency and extrinsic modulation due to the non-volatile electric-control of the current injection in the 2DEG. The non-volatile control of the SOT effective field is evidenced by reproducible inversion of the SOTs after voltage pulses initialization, opening the way to reconfigurable SOT memories and logic-gate architectures.

Spin-orbit effects appearing in topological insulators (TI) and at Rashba interfaces are currently revolutionizing how we can manipulate spins and have led to several newly discovered effects, from spin-charge interconversion and spin-orbit torques to novel magnetoresistance phenomena. In particular, a puzzling magnetoresistance has been evidenced as bilinear in electric and magnetic fields. Here, we report the observation of bilinear magnetoresistance (BMR) in strained HgTe, a prototypical TI. We show that both the amplitude and sign of this BMR can be tuned by controlling with an electric gate the relative proportions of the opposite contributions of opposite surfaces. At magnetic fields of 1 T, the magnetoresistance is of the order of 1% and has a larger figure of merit than previously measured TIs. We propose a theoretical model giving a quantitative account of our experimental data. This phenomenon, unique to TI, offers novel opportunities to tune their electrical response for spintronics.

Les couches minces et les nanostructures utilisées en électronique de spin sont le siège de différents effets : magnétorésistances, transfert de spin et effets spin-orbite. Ces effets permettent en particulier la lecture et le contrôle de l’état d’aimantation, jusqu’à son renversement.

Whereas conventional spintronics uses the exchange interaction in a ferromagnetic material to manipulate spin currents, spin-orbit coupling can now be used to generate or detect spin currents, possibly in absence of any ferromagnetic element. We have shown that Rashba interfaces such as Ag/Bi1, LAO/STO2,3 and Al/STO4 possess this ability, with giant Rashba-Edelstein lengths. Moreover, in these quantum materials the spincharge conversion can be tunable by a gate voltage, and it is even possible to reverse the sign of the conversion. This Post-Doc project aims at exploring the possibilities offered by these features in oxide twodimensional electron gas and in ferroelectric semiconductors, in particular for the development of the reading part of innovative memory and logic spin-orbit devices5.

In this work, we study the manipulation and the detection of the magnetic state and switching modes of a Permalloy disk, using a non-local spin-valve with dual CoFe injectors and with the disk acting as the detector electrode. Applying simultaneously external magnetic fields and spin currents from the injectors, we demonstrate the possibility to use the spin torque created by the spin current to modulate the switching modes and switching fields of the disk, following the disentanglement of the influence of Joule heating. Moreover, by engineering the device to have a very small overlap of the spin conduit with one side of the disk, we demonstrate how, with the help of a first-order reversal curve analysis, we can extract the precise details of the switching from the monodomain to the vortex state, including the chirality of the system without the need for direct imaging.

The rare-earth-free ferrimagnet Mn4N has attractive features for spintronics applications, because it possesses a perpendicular magnetization, due to a relatively large magnetic anisotropy constant of similar to 10(5)Jm(-3) and a small spontaneous magnetization of similar to 100 kAm(-1), and a large spin polarization (P = 0.8). More crucially, it is possible to reach the magnetic compensation at room temperature, by tuning its constituent elements in compounds such as Mn4-xNixN and Mn4-xCoxN. This is particularly interesting for spin-torque-based spintronics applications, because at the vicinity of the magnetization and/or angular momentum compensation points, the switching currents can be reduced significantly, thereby leading to lower switching energies and higher switching speed. In this review article, we emphasize the importance of epitaxial growth of Mn4N films by comparing the results obtained on two different substrates, MgO(001) and SrTiO3(001). We then present the achievement of ultrafast current-induced domain wall motion (CIDWM) in Mn4N microstrips, and study the magnetic compensations in Mn4-xNixN and Mn4-xCoxN at room temperature, proved by x-ray magnetic circular dichroism measurements. Finally, we offer future prospects for such Mn4N-based compensated ferrimagnets.