arXiv subjects

Edurne Sagasta

Publications and source records attributed to Edurne Sagasta.

12 recordsLinked to original sources

arXiv2022

Emergence of large spin-charge interconversion at an oxidized Cu/W interface

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, such as the magnetoelectric spin-orbit (MESO) logic, 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. 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 (WO$_x$). We determine that the SCI occurs at the Cu/WO$_x$ interface with a temperature-independent interfacial spin-loss conductance of $G_{||} \approx$ 20 $\times$ 10$^{13} Ω^{-1}m^{-2}$ and an interfacial spin-charge conductivity $σ_{SC}=-$1610 $Ω^{-1}cm^{-1}$ at 10 K ($-$830 $Ω^{-1}cm^{-1}$ at 300 K). This corresponds to an efficiency given by the inverse Edelstein length $λ_{IEE}=-$0.76 nm at 10 K ($-$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 is a promising candidate for the magnetic readout in MESO logic devices.

cond-mat.mes-hall↗

arXiv2021

Paramagnetic spin Hall magnetoresistance

Spin Hall magnetoresistance (SMR) refers to a resistance change in a metallic film reflecting the magnetization direction of a magnet attached to the film. The mechanism of this phenomenon is spin exchange between conduction-electron spins and magnetization at the interface. SMR has been used to read out information written in a small magnet and to detect magnetization dynamics, but it has been limited to magnets; magnetic ordered phases or instability of magnetic phase transition has been believed to be indispensable. Here, we report the observation of SMR in a paramagnetic insulator Gd$_{3}$Ga$_{5}$O$_{12}$ (GGG) without spontaneous magnetization combined with a Pt film. The paramagnetic SMR can be attributed to spin-transfer torque acting on localized spins in GGG. We determine the efficiencies of spin torque and spin-flip scattering at the Pt/GGG interface, and demonstrate these quantities can be tuned with external magnetic fields. The results clarify the mechanism of spin-transport at a metal/paramagnetic insulator interface, which gives new insight into the spintronic manipulation of spin states in paramagnetic systems.

cond-mat.mtrl-sci↗

arXiv2020

Quantification of interfacial spin-charge conversion in metal/insulator hybrid structures by generalized boundary conditions

We present and verify experimentally a universal theoretical framework for the description of spin-charge interconversion in non-magnetic metal/insulator structures with interfacial spin-orbit coupling (ISOC). Our formulation is based on drift-diffusion equations supplemented with generalized boundary conditions. The latter encode the effects of ISOC and relate the electronic transport in such systems to spin loss and spin-charge interconversion at the interface, which are parameterized, respectively, by $G_{\parallel/\perp}$ and $σ_{\rm{sc/cs}}$. We demonstrate that the conversion efficiency depends solely on these interfacial parameters. We apply our formalism to two typical spintronic devices that exploit ISOC: a lateral spin valve and a multilayer Hall bar, for which we calculate the non-local resistance and the spin Hall magnetoresistance, respectively. Finally, we perform measurements on these two devices with a BiO$_x$/Cu interface and verify that transport properties related to the ISOC are quantified by the same set of interfacial parameters.

cond-mat.mes-hall↗

arXiv2020

Spin-orbit magnetic state readout in scaled ferromagnetic/heavy metal nanostructures

Efficient detection of the magnetic state at nanoscale dimensions is an important step to utilize spin logic devices for computing. Magnetoresistance effects have been hitherto used in magnetic state detection, but they suffer from energetically unfavorable scaling and do not generate an electromotive force that can be used to drive a circuit element for logic device applications. Here, we experimentally show that a favorable miniaturization law is possible via the use of spin-Hall detection of the in-plane magnetic state of a magnet. This scaling law allows us to obtain a giant signal by spin Hall effect in CoFe/Pt nanostructures and quantify an effective spin-to-charge conversion rate for the CoFe/Pt system. The spin-to-charge conversion can be described as a current source with an internal resistance, i.e., it generates an electromotive force that can be used to drive computing circuits. We predict that the spin-orbit detection of magnetic states can reach high efficiency at reduced dimensions, paving the way for scalable spin-orbit logic devices and memories.

cond-mat.mes-hall↗

arXiv2019

Spin diffusion length of Permalloy using spin absorption in lateral spin valves

We employ the spin absorption technique in lateral spin valves to extract the spin diffusion length of Permalloy (Py) as a function of temperature and resistivity. A linear dependence of the spin diffusion length with conductivity of Py is observed, evidencing that Elliott-Yafet is the dominant spin relaxation mechanism in Permalloy. Completing the data set with additional data found in literature, we obtain $λ_{Py}= (0.91\pm 0.04) (fΩm^2)/ρ_{Py}$.

cond-mat.mes-hall↗

arXiv2019

Interfacial mechanism in the anomalous Hall effect of Co/Bi$_2$O$_3$ bilayers

Oxide interfaces are a source of spin-orbit coupling which can lead to novel spin-to-charge conversion effects. In this work the contribution of the Bi$_2$O$_3$ interface to the anomalous Hall effect of Co is experimentally studied in Co/Bi$_2$O$_3$ bilayers. We evidence a variation of 40% in the AHE of Co when a Bi$_2$O$_3$ capping layer is added to the ferromagnet. This strong variation is attributed to an additional source of asymmetric transport in Co/Bi$_2$O$_3$ bilayers that originates from the Co/Bi$_2$O$_3$ interface and contributes to the skew scattering.

cond-mat.mes-hall↗

arXiv2019

Relation between spin Hall effect and anomalous Hall effect in 3$d$ ferromagnetic metals

We study the mechanisms of the spin Hall effect (SHE) and anomalous Hall effect (AHE) in 3$d$ ferromagnetic metals (Fe, Co, permalloy (Ni$_{81}$Fe$_{19}$; Py), and Ni) by varying their resistivities and temperature. At low temperatures where the phonon scattering is negligible, the skew scattering coefficients of the SHE and AHE in Py are related to its spin polarization. However, this simple relation breaks down for Py at higher temperatures as well as for the other ferromagnetic metals at any temperature. We find that, in general, the relation between the SHE and AHE is more complex, with the temperature dependence of the SHE being much stronger than that of AHE.

cond-mat.mes-hall↗

arXiv2018

Unveiling the mechanisms of the spin Hall effect in Ta

Spin-to-charge current interconversions are widely exploited for the generation and detection of pure spin currents and are key ingredients for future spintronic devices including spin-orbit torques and spin-orbit logic circuits. In case of the spin Hall effect, different mechanisms contribute to the phenomenon and determining the leading contribution is peremptory for achieving the largest conversion efficiencies. Here, we experimentally demonstrate the dominance of the intrinsic mechanism of the spin Hall effect in highly-resistive Ta. We obtain an intrinsic spin Hall conductivity for $β$-Ta of -820$\pm$120 ($\hbar$/e) $Ω^{-1}cm^{-1}$ from spin absorption experiments in a large set of lateral spin valve devices. The predominance of the intrinsic mechanism in Ta allows us to linearly enhance the spin Hall angle by tuning the resistivity of Ta, reaching up to -35$\pm$3%, the largest reported value for a pure metal.

cond-mat.mes-hall↗

arXiv2017

Large room temperature spin-to-charge conversion signals in a few-layer graphene/Pt lateral heterostructure

Electrical generation and detection of pure spin currents without the need of magnetic materials are key elements for the realization of full electrically controlled spintronic devices. In this framework, achieving a large spin-to-charge conversion signal is crucial, since considerable outputs are needed for plausible applications. Unfortunately, the values obtained so far have been rather low. Here we exploit the spin Hall effect by using Pt, a non-magnetic metal with strong spin-orbit coupling, to generate and detect pure spin currents in a few-layer graphene channel. Furthermore, the outstanding properties of graphene, with long distance spin transport and higher electrical resistivity than metals, allows us to achieve in our graphene/Pt lateral heterostructures the largest spin-to-charge voltage signal at room temperature reported so far in the literature. Our approach opens up exciting opportunities towards the implementation of spin-orbit-based logic circuits and all electrical control of spin information without magnetic field.

cond-mat.mes-hall↗

arXiv2016

Spin Hall magnetoresistance as a probe for surface magnetization in Pt/CoFe$_2$O$_4$ bilayers

We study the spin Hall magnetoresistance (SMR) in Pt grown $\textit{in situ}$ on CoFe$_2$O$_4$ (CFO) ferrimagnetic insulating (FMI) films. A careful analysis of the angle-dependent and field-dependent longitudinal magnetoresistance indicates that the SMR contains a contribution that does not follow the bulk magnetization of CFO but it is a fingerprint of the complex magnetism at the surface of the CFO layer, thus signaling SMR as a tool for mapping surface magnetization. A systematic study of the SMR for different temperatures and CFO thicknesses gives us information impossible to obtain with any standard magnetometry technique. On one hand, surface magnetization behaves independently of the CFO thickness and does not saturate up to high fields, evidencing that the surface has its own anisotropy. On the other hand, characteristic zero-field magnetization steps are not present at the surface while they are relevant in the bulk, strongly suggesting that antiphase boundaries are the responsible of such intriguing features. In addition, a contribution from ordinary magnetoresistance of Pt is identified, which is only distinguishable due to the low resistivity of the $\textit{in-situ}$ grown Pt.

cond-mat.mes-hall↗

arXiv2016

Tuning the spin Hall effect of Pt from the moderately dirty to the superclean regime

We systematically measure and analyze the spin diffusion length and the spin Hall effect in Pt with a wide range of conductivities using the spin absorption method in lateral spin valve devices. We observe a linear relation between the spin diffusion length and the conductivity, evidencing that the spin relaxation in Pt is governed by the Elliott-Yafet mechanism. We find a single intrinsic spin Hall conductivity ($σ_{SH}^{int}=1600\pm150\: Ω^{-1}cm^{-1}$) for Pt in the full range studied which is in good agreement with theory. For the first time we have obtained the crossover between the moderately dirty and the superclean scaling regimes of the spin Hall effect by tuning the conductivity. This is equivalent to that obtained for the anomalous Hall effect. Our results explain the spread of the spin Hall angle values in the literature and find a route to maximize this important parameter.

cond-mat.mes-hall↗

arXiv2016

Hanle Magnetoresistance in Thin Metal Films with Strong Spin-Orbit Coupling

We report measurements of a new type of magnetoresistance in Pt and Ta thin films. The spin accumulation created at the surfaces of the film by the spin Hall effect decreases in a magnetic field because of the Hanle effect, resulting in an increase of the electrical resistance as predicted by Dyakonov [PRL 99, 126601 (2007)]. The angular dependence of this magnetoresistance resembles the recently discovered spin Hall magnetoresistance in Pt/Y3Fe5O12 bilayers, although the presence of a ferromagnetic insulator is not required. We show that this Hanle magnetoresistance is an alternative, simple way to quantitatively study the coupling between charge and spin currents in metals with strong spin-orbit coupling.

cond-mat.mes-hall↗