As CMOS technologies face challenges in dimensional and voltage scaling, the demand for novel logic devices has never been greater, with spin-based devices offering scaling potential, at the cost of significantly high switching energies. Alternatively, magnetoelectric materials are predicted to enable low-power magnetization control, a solution with limited device-level results. Here, we demonstrate voltage-based magnetization switching and reading in nanodevices at room temperature, enabled by exchange coupling between multiferroic BiFeO 3 and ferromagnetic CoFe, for writing, and spin-to-charge current conversion between CoFe and Pt, for reading. We show that, upon the electrical switching of the BiFeO 3 , the magnetization of the CoFe can be reversed, giving rise to different voltage outputs. Through additional microscopy techniques, magnetization reversal is linked with the polarization state and antiferromagnetic cycloid propagation direction in the BiFeO 3 . This study constitutes the building block for magnetoelectric spin-orbit logic, opening a new avenue for low-power beyond-CMOS technologies.

Spin-orbitronic devices can integrate memory and logic by exploiting spin-charge interconversion (SCI), which is optimized by design and materials selection. In these devices, interfaces are crucial elements as they can prohibit or promote spin flow in a device as well as possess spin-orbit coupling resulting in interfacial SCI. Therefore, investigation of interfaces in spin-orbitronic devices is important. Here, we study the origin of SCI in a Py/Cu/W lateral spin valve and quantify its efficiency. An exhaustive characterization of the interface between Cu and W electrodes uncovers the presence of an oxidized layer (WOx). We determine that the SCI occurs at the Cu/WOx interface with a temperature-independent interfacial spin-loss conductance of G(broken vertical bar broken vertical bar) approximate to 20 x 10(13) Omega(-1) m(-2) and an interfacial spin-charge conductivity sigma(SC) = -1600 Omega(-1)cm(-1) at 10 K (-800 Omega(-1) cm(-1) at 300 K). This corresponds to an efficiency given by the inverse Edelstein length lambda(IEE) = -0.8 nm at 10 K (-0.4 nm at 300 K), which is remarkably larger than in metal/metal and metal/oxide interfaces and bulk heavy metals. The large SCI efficiency at such an oxidized interface makes it a promising candidate for the magnetic readout in MESO logic devices.

With the deceleration of dimensional and voltage scaling in CMOS technologies, the demand for novel logic devices has never been greater. While spin-based devices present a major opportunity towards favorable scaling, switching energies are still orders of magnitude above the expected values. Alternatively, magnetoelectric materials are predicted to enable low-power control of magnetization, a relatively unexplored pathway with sparse results at a device level. Here, we demonstrate voltage-based magnetization switching and reading in nanodevices at room temperature, enabled by exchange coupling between multiferroic BiFeO$_3$ and ferromagnetic CoFe, for the writing, and spin-to-charge current conversion between CoFe and Pt, for the reading. Unlike other current-based spintronic devices, magnetization writing is driven solely by voltage pulses. We show that, upon electrical switching of the BiFeO$_3$, the magnetization of the CoFe can be reversed, giving rise to different voltage outputs. The voltage-induced switching is supported through a combination of piezoresponse, magnetic force microscopy, and scanning nitrogen-vacancy magnetometry, where magnetization reversal is linked with the polarization state and antiferromagnetic cycloid propagation direction in the BiFeO$_3$. This study constitutes the building block for magnetoelectric spin-orbit logic, as well as a new avenue for low-power beyond-CMOS technologies.

The development of spin-orbitronic devices, such as magnetoelectric spin-orbit logic devices, calls for materials with a high resistivity and a high spin-charge interconversion efficiency. One of the most promising candidates in this regard is sputtered BixSe1-x. Although there are several techniques to quantify spin-charge interconversion, reported values to date for sputtered BixSe1-x have often been overestimated due to spurious effects related to local currents combined with a lack of understanding of the effect of the interfaces and the use of approximations for unknown parameters, such as the spin diffusion length. In the present study, nonlocal spin valves are used to inject pure spin currents into BixSe1-x, allowing us to directly obtain its spin diffusion length as well as its spin Hall angle, from 10 K up to 300 K. These values, which are more accurate than those previously reported in sputtered BixSe1-x, evidence that the efficiency of this material is not exceptional. Indeed, the figure of merit for spin-charge interconversion, given by the product of these two parameters, is slightly under 1 nm. Our work demonstrates the importance of considering all material parameters and interfaces when quantifying the spin transport properties of materials with strong spin-orbit coupling.

One of the major obstacles to realizing spintronic devices such as MESO logic devices is the small signal magnitude used for magnetization readout, making it important to find materials with high spin-to-charge conversion efficiency. Although intermixing at the junction of two materials is a widely occurring phenomenon, its influence on material characterization and the estimation of spin-to-charge conversion efficiencies are easily neglected or underestimated. Here, we demonstrate all-electrical spin-to-charge conversion in BixSe1-x nanodevices and show how the conversion efficiency can be overestimated by tens of times depending on the adjacent metal used as a contact. We attribute this to the intermixing-induced compositional change and the properties of a polycrystal that lead to drastic changes in resistivity and spin Hall angle. Strategies to improve the spin-to-charge conversion signal in similar structures for functional devices are discussed.

The conversion of spin currents polarized in different directions into charge currents is a keystone for novel spintronic devices. Van der Waals heterostructures with tailored symmetry are a very appealing platform for such a goal. Here, by performing nonlocal spin precession experiments, we demonstrate the spin-to-charge conversion (SCC) of spins oriented in all three directions (x, y, and z). By analyzing the magnitude and temperature dependence of the signal in different configurations, we argue that the different SCC components measured are likely due to spin-orbit proximity and broken symmetry at the twisted graphene/NbSe2 interface. Such efficient omnidirectional SCC opens the door to the use of new architectures in spintronic devices, from spin-orbit torques that can switch any magnetization to the magnetic state readout of magnetic elements pointing in any direction.

We present the first experimental realization of a magnetoelectric spin-orbit (MESO) logic device at room temperature. Two logic states are determined by the magnetization direction of a nanostructured CoFe element, which is switched by a magnetoelectric BiFeO3 layer (WRITE) and detected through spin-to-charge conversion effect in a Pt element (READ).

Ferromagnet (FM)\ifmmode\text{\textcelsius}\else\textcelsius\fi{}heavy-metal (HM) nanostructures can be used for magnetic state readout in the proposed magnetoelectric spin-orbit logic by locally injecting a spin-polarized current and measuring the spin-to-charge conversion via the spin Hall effect. However, this local configuration is prone to spurious signals. Here, we address spurious Hall effects that can contaminate the spin Hall signal in these FM/HM T-shaped nanostructures. The most pronounced Hall effects in our ${\mathrm{Co}}_{50}{\mathrm{Fe}}_{50}/\mathrm{Pt}$ nanostructures are the planar Hall effect and the anomalous Hall effect generated in the ferromagnetic nanowire. We find that the planar Hall effect, induced by misalignment between magnetization and current direction in the ferromagnetic wire, is manifested as a shift in the measured baseline resistance, but does not alter the spin Hall signal. In contrast, the anomalous Hall effect, arising from the charge-current distribution within the FM, adds to the spin Hall signal. However, the effect can be made insignificant by minimizing the shunting effect via proper design of the device. We conclude that local spin injection in FM/HM nanostructures is a suitable tool for measuring spin Hall signals and, therefore, a valid method for magnetic state readout in prospective spin-based logic.

Spin-charge interconversion in systems with spin-orbit coupling has provided a new route for the generation and detection of spin currents in functional devices for memory and logic such as spin-orbit torque switching in magnetic memories or magnetic state reading in spin-based logic. Disentangling the bulk (spin Hall effect) from the interfacial (inverse spin galvanic effect) contribution has been a common issue to properly quantify the spin-charge interconversion in these systems, being the case of Au paradigmatic. Here, we obtain a large spin-charge interconversion at a highly conducting Au/Cu interface which is experimentally shown to arise from the inverse spin galvanic effect of the interface and not from the spin Hall effect of bulk Au. We use two parameters independent of the microscopic details to properly quantify the spin-charge interconversion and the spin losses due to the interfacial spin-orbit coupling, providing an adequate benchmarking to compare with any spin-charge interconversion system. The good performance of this metallic interface, not based in Bi, opens the path to the use of much simpler light/heavy metal systems.

The efficient detection of a magnetic state at nanoscale dimensions is important for the development of spin-logic devices. Magnetoresistance effects can be used to detect magnetic states, but they do not generate an electromotive force (that is, a voltage) or a current that can be used to drive a circuit element for logic device applications. Here we report a favourable scaling law for the detection of an in-plane magnetic state of a magnet by using the inverse spin Hall effect in cobalt–iron/platinum (CoFe/Pt) nanostructured devices. By reducing the dimensions of the device, we obtain a large spin Hall signal of 0.3 Ω at room temperature and quantify an effective spin-to-charge conversion rate for the ferromagnetic/heavy metal system. We predict that this spin–orbit detection of magnetic states could be used to drive spin-logic circuits. A favourable scaling law for the magnetic state readout of CoFe/Pt nanostructure devices allows large spin Hall signals of 0.3 Ω at room temperature to be obtained, which could be useful in the development of spin-logic devices.

600 mV magneto-electric switching in 30 nm La-doped BiFeO 3 multiferroic oxide and a proof of concept 7 μV spin-orbit signal output in Pt / CoFe local spin injection device with 100 μA supply current were experimentally demonstrated at room temperature for the 1 st time. Also demonstrated was a path towards 70 mV spin orbit output using Bi 2 Se 3 in a local spin injection device. These are key accomplishments for WRITE and READ building blocks, respectively, toward realization of a magneto-electric spin-orbit (MESO) energy-efficient logic device. Moreover, the 1 st generation of a MESO logic device with a functional READ unit is demonstrated.

We report on the discovery and transport study of the superconducting ground state present at the (111) LaAlO3/SrTiO3 (LAO/STO) interface. The superconducting transition is consistent with a Berezinskii-Kosterlitz-Thouless transition and its two-dimensional nature is further corroborated by the anisotropy of the critical magnetic field, as calculated by Tinkham. The estimated superconducting layer thickness and coherence length are 10 and 60 nm, respectively. The results of this work provide insight to clarify the microscopic details of superconductivity in LAO/STO interfaces, in particular in what concerns the link with orbital symmetry.

thesis describes research that was executed as a combined Master Research Project in Applied Physics and Materials Science and Engineering, leading up to a double MSc degree. The (100)-oriented LaAlO3/SrTiO3 (LAO/STO) interface has been subject of intense study since the discovery of the two-dimensional electron system (2DES) in this heterostructure. Recently, it has been observed that the LAO/STO(111) interface also hosts a 2DES but its physical properties are relatively unexplored. This work presents a systematic magnetotransport study on the 2DES of this structure. We report on superconductivity in a patterned interface with a 10 uc LAO thin film. The evolution of the superconducting phase at the LAO/STO(111) interface is under investigation. The superconducting phase is observed to be gate tunable and, at optimal doping, the BKT temperature, the maximum critical current and the critical magnetic field are observed to be ~70 mK, ~ 200 nA and ~21 mT, respectively. Furthermore, we observe that interface conduction can be modelled by a random array of Josephson junctions formed by superconducting puddles due to the inhomogeneous character of the interface.