arXiv subjects

Eoin Dolan

Publications and source records attributed to Eoin Dolan.

9 recordsLinked to original sources

arXiv2026

Gate-tunable charge-spin interconversion in graphene/heavy-metal heterostructures

Spintronics has emerged as a promising field for next-generation devices, offering functionalities beyond complementary metal-oxide-semiconductor (CMOS). A critical challenge in spintronics is to develop systems that can efficiently generate spin currents and enable their long-distance transport. Here, we demonstrate a graphene (Gr)/heavy metal (HM) heterostructure system that combines strong charge-spin interconversion efficiency, induced by the spin Hall effect, with a long spin diffusion length. By employing an industry-friendly magnetron sputtering technique, we deposit HM layers onto few-layer Gr while minimizing structural damage. The proximity effect from the HM enhances the spin Hall angle of Gr while limiting the reduction in its spin diffusion length. Additionally, the spin Hall angle can be tuned via an applied gate voltage, offering high controllability of the system. Importantly, these properties are observed across heterostructures composed of different HMs, indicating the generality of this approach. Our findings establish Gr/HM heterostructures as a scalable and versatile platform for spin current generation, paving the way for advanced spintronic devices with high efficiency, long spin propagation, and straightforward fabrication processes.

cond-mat.mes-hall↗

arXiv2025

Direct demonstration of time-reversal-symmetry-breaking spin injection from a compensated magnet

The injection, propagation and detection of spin currents are essential physical processes in spintronics. So far, the separation of charge and spin currents was facilitated by the electrical spin injection from a ferromagnet (FM) or the injection by a relativistic spin Hall effect. The devices employed are lateral spin valves comprising spatially separated injection and detection electrodes, connected by a spin-propagation channel. The time-reversal symmetry (TRS) breaking FM spin injection is realized in a geometry with an electrical bias applied between the injection electrode and the channel and is modelled by a conserved spin-polarized drift current. In contrast, the spin injection by the T-symmetric relativistic spin Hall mechanism is driven by an electrical bias applied across the injection electrode alone, and is modelled by a non-conserved spin current transverse to the applied bias. In this work, we use a lateral spin valve with a Mn5Si3 injection electrode to directly demonstrate a TRS-breaking spin injection from a compensated magnet with a vanishing net magnetization. Specifically, the TRS-breaking is demonstrated by the fact that switching between time-reversed states of the compensated magnet changes the detected spin signal. Moreover, the TRS-breaking nature of the spin injection is observed in both experimental geometries with the different electrical biasing, while using the same detection electrode. We show that this unconventional spin-injection is consistent with different magnitudes and propagation angles of electrical currents in the spin-up and spin-down channel in a d-wave altermagnet. Here our symmetry analysis and first-principles calculations are based on the compensated collinear altermagnetic order which has provided a comprehensive microscopic interpretation of earlier structural, magnetic, and anomalous Hall and Nernst measurements in Mn5Si3 thin films.

cond-mat.mes-hall↗

arXiv2025

Measuring the magnetic anisotropy of the spin Hall effect and spin relaxation length in nickel and permalloy via electrical spin injection

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.

cond-mat.mes-hall↗

arXiv2025

Gate tunable spin-charge interconversion in a graphene/ReS$_{2}$ heterostructure up to room temperature

Graphene is a material with great potential in the field of spintronics, combining good conductivity with low spin--orbit coupling (SOC), which allows for the transport of spin currents over long distances. However, this lack of SOC also limits the capacity for manipulating spin current. A key strategy to address this limitation is to induce SOC in graphene via proximity to other two-dimensional (2D) materials. Such proximity-induced SOC can enable spin--charge interconversion (SCI) in graphene, with potential applications in next-generation logic devices. Here, we place graphene in close proximity to the room-temperature ferroelectric candidate ReS$_\mathrm{2}$, inducing SCI for both in-plane and out-of-plane polarized spin current. We attribute the SCI for in-plane polarized current to either the Rashba--Edelstein effect (REE) or the unconventional spin Hall effect (SHE) at the graphene/ReS$_\mathrm{2}$ interface, and the SCI for out-of-plane polarized current to either the conventional SHE in the proximitised graphene, or the unconventional SHE in the bulk of the ReS$_\mathrm{2}$. SCI due to in-plane spin is characterised over a wide range of temperature, up to 300 K and a range of gate voltages.

cond-mat.mes-hall↗

arXiv2025

Orbital Hall conductivity and orbital diffusion length of Vanadium thin films by Hanle magnetoresistance

In spintronics, the spin Hall effect has been widely used to generate and detect spin currents in materials with strong spin-orbit coupling such as Pt and Ta. Recently, its orbital counterpart has drawn attention as a new tool to generate and detect orbital currents and thus investigate orbital transport parameters. In this study, we investigate vanadium (V), a $3d$ transition metal with weak spin-orbit coupling but with a theoretically large orbital Hall conductivity. We measure a large Hanle magnetoresistance in V thin films with a magnitude comparable to that of heavy metals and at least one order of magnitude higher than the spin Hall magnetoresistance observed in a Y$_3$Fe$_5$O$_{12}$/V bilayer, pointing to the orbital Hall origin of the effect. A fit of the magnetic-field dependence and thickness dependence of the Hanle magnetoresistance to the standard diffusion model allows us to quantify the orbital diffusion length (~2 nm) and the orbital Hall conductivity (~78 ($\hbar/2e$) $\Omega^{-1}$cm$^{-1}$) of V. The obtained orbital Hall conductivity is two orders of magnitude smaller than theoretical calculations of the intrinsic value, suggesting there is an important role of disorder.

cond-mat.mes-hall↗

arXiv2024

Gate-tunable spin Hall effect in trilayer graphene/group-IV monochalcogenide van der Waals heterostructures

Spintronic devices require materials that facilitate effective spin transport, generation, and detection. In this regard, graphene emerges as an ideal candidate for long-distance spin transport owing to its minimal spin-orbit coupling, which, however, limits its capacity for effective spin manipulation. This problem can be overcome by putting spin-orbit coupling materials in close contact to graphene leading to spin-orbit proximity and, consequently, efficient spin-to-charge conversion through mechanisms such as the spin Hall effect. Here, we report and quantify the gate-dependent spin Hall effect in trilayer graphene proximitized with tin sulfide (SnS), a group-IV monochalcogenide which has recently been predicted to be a viable alternative to transition-metal dichalcogenides for inducing strong spin-orbit coupling in graphene. The spin Hall angle exhibits a maximum around the charge neutrality point of graphene up to room temperature. Our findings expand the library of materials that induce spin-orbit coupling in graphene to a new class, group-IV monochalcogenides, thereby highlighting the potential of two-dimensional materials to pave the way for the development of innovative spin-based devices and future technological applications.

cond-mat.mes-hall↗

arXiv2024

Control of charge-spin interconversion in van der Waals heterostructures with chiral charge density waves

A charge density wave (CDW) represents an exotic state in which electrons are arranged in a long range ordered pattern in low-dimensional materials. Although our understanding of the fundamental character of CDW has been enriched after extensive studies, its relationship with functional phenomena remains relatively limited. Here, we show an unprecedented demonstration of a tunable charge-spin interconversion (CSI) in graphene/1T-TaS$_2$ van der Waals heterostructures by manipulating the distinct CDW phases in 1T-TaS$_2$. Whereas CSI from spins polarized in all three directions are observed in the heterostructure when the CDW phase does not show commensurability, the output of one of the components disappears and the other two are enhanced when the CDW phase becomes commensurate. The experimental observation is supported by first-principles calculations, which evidence that chiral CDW multidomains are at the origin of the switching of CSI. Our results uncover a new approach for on-demand CSI in low-dimensional systems, paving the way for advanced spin-orbitronic devices.

cond-mat.mtrl-sci↗

arXiv2023

Twist-angle tunable spin texture in WSe$_2$/graphene van der Waals heterostructures

Angle-twisting engineering has emerged as a powerful tool for modulating electronic properties in van der Waals heterostructures. Recent theoretical works have predicted the modulation of spin texture in graphene-based heterostructures by twist angle, although an experimental verification is missing. Here, we demonstrate the tunability of the spin texture and associated spin-charge interconversion with twist angle in WSe$_2$/graphene heterostructures by using spin precession experiments. For specific twist angles, we experimentally detect a spin component radial with the electron's momentum, in addition to the standard orthogonal component. Our results show that the helicity of the spin texture can be reversed by angle twisting, highlighting its critical role on the spin-orbit properties of WSe$_2$/graphene heterostructures and paving the way for the development of novel spin-twistronic devices.

cond-mat.mes-hall↗

arXiv2023

Gate-tunable spin Hall effect in an all-light-element heterostructure: graphene with copper oxide

Graphene is a light material for long-distance spin transport due to its low spin-orbit coupling, which at the same time is the main drawback to exhibit a sizeable spin Hall effect. Decoration by light atoms has been predicted to enhance the spin Hall angle in graphene while retaining a long spin diffusion length. Here, we combine a light metal oxide (oxidized Cu) with graphene to induce the spin Hall effect. Its efficiency, given by the product of the spin Hall angle and the spin diffusion length, can be tuned with the Fermi level position, exhibiting a maximum (1.8 $\pm$ 0.6 nm at 100 K) around the charge neutrality point. This all-light-element heterostructure shows a larger efficiency than conventional spin Hall materials. The gate-tunable spin Hall effect is observed up to room temperature. Our experimental demonstration provides an efficient spin-to-charge conversion system free from heavy metals and compatible with large-scale fabrication.

cond-mat.mes-hall↗