arXiv subjects

Albert Fert

Publications and source records attributed to Albert Fert.

At least 19 recordsLinked to original sources

arXiv2025

Dimensionality Enhanced Out-of-Plane Spin Currents in NbIrTe$_4$ for Efficient Field-Free Switching of Perpendicular Magnetization

Efficient generation of out-of-plane (OOP) spin currents is crucial for advanced spintronic memory applications. However, the theoretical understanding and experimental implementation of robust OOP spin currents for high-density and low-power magnetization switching remain significant challenges of spintronics. Here, we demonstrate that transitioning NbIrTe$_4$ from a two-dimensional quantum spin Hall insulator to a three-dimensional type-II Weyl semimetal markedly enhances OOP spin current generation. The bulk topological Weyl semimetal nature of NbIrTe$_4$, characterized by its Weyl cone, significantly enhances the OOP spin Berry curvature, enabling an unprecedented OOP spin Hall conductivity exceeding $10^5\hbar/2e$ $\Omega^{-1}m^{-1} $. This enhancement, surpassing the in-plane component by more than fourfold, enables efficient and field-free spin-orbit torque (SOT) switching of perpendicular magnetization with a low current density of 1.4 MA/cm$^2$. The improved spin Hall conductivity reduces the overall power consumption by more than two orders of magnitude compared to existing systems, such as heavy metals. Our findings highlight the pivotal role of dimensionality in harnessing robust OOP spin currents in topological Weyl semimetals, paving the way for the development of high-density, low-power spintronic memory technologies.

cond-mat.mes-hall↗

arXiv2024

Large Chiral Orbital Texture and Orbital Edelstein Effect in Co/Al Heterostructure

Recent experiments by S. Krishnia et al., Nano Lett. 23, 6785 (2023) reported an unprecedentedly large enhancement of torques upon inserting thin Al layer in Co/Pt heterostructure that suggested the presence of a Rashba-like interaction at the metallic Co/Al interface. Based on first-principles calculations, we reveal the emergence of a large helical orbital texture in reciprocal space at the interfacial Co layer, whose origin is attributed to the orbital Rashba effect due to the formation of the surface states at the Co/Al interface and where spin-orbit coupling is found to produce smaller contributions with a higher-order winding of the orbital momentum. Our results unveil that the orbital texture gives rise to a non-equilibrium orbital accumulation producing large current-induced torques, thus providing an essential theoretical background for the experimental data and advancing the use of orbital transport phenomena in all-metallic magnetic systems with light elements.

cond-mat.mtrl-sci↗

arXiv2024

Interfacial spin-orbitronic effects controlled with different oxidation levels at the Co|Al interface

Perpendicular magnetic anisotropy (PMA) and Dzyaloshinskii-Moriya interactions are key interactions in modern spintronics. These interactions are thought to be dominated by the oxidation of the Co|Al interface in the archetypal Platinum-Cobalt-Aluminum oxide system. Here, we observe a double sign change in the anisotropy and about threefold variation in interfacial chiral interaction, influenced not only by the oxidation, but also by the metallic Al thickness. Contrary to previous assumptions about negligible spin-orbit effects at light metal interfaces, we not only observe strong PMA with fully oxidized Al, decreasing and turning negative (in-plane) with less oxygen at the Co|Al interface, we also observe that the magnetic anisotropy reverts to positive (out-of-plane) values at fully metallic Co|Al interface. These findings suggest modification in Co d band via Co|Al orbital hybridization, an effect supported by X-ray absorption spectroscopy and ab initio theory calculations, highlighting the key impact of strain on interfacial mechanisms at fully metallic Co|Al interface.

cond-mat.mtrl-sci↗

arXiv2024

A seamless graphene spin valve based on proximity to van der Waals magnet Cr$_2$Ge$_2$Te$_6$

Pristine graphene is potentially an ideal medium to transport spin information. Proximity effects, where a neighbouring material is used to alter the properties of a material in adjacent (or proximitized) regions, can also be used in graphene to generate and detect spins by acquiring spin-orbit coupling or magnetic exchange coupling. However, the development of seamless spintronic devices that are based uniquely on proximity effects remains challenging. Here, we report a two-dimensional graphene spin valve that is enabled by proximity to the van der Waals magnet Cr$_2$Ge$_2$Te$_6$. Spin precession measurements show that graphene acquires both spin-orbit coupling and magnetic exchange coupling when interfaced with the Cr$_2$Ge$_2$Te$_6$. This leads to spin generation by both electrical spin injection and the spin Hall effect, while retaining long-distance spin transport. The simultaneous presence of spin-orbit coupling and magnetic exchange coupling also leads to a sizeable anomalous Hall effect.

cond-mat.mes-hall↗

arXiv2024

Symmetry Origin and Microscopic Mechanism of Electrical Magnetochiral Anisotropy in Tellurium

Non-linear transport effects in response to external magnetic fields, i.e. electrical magnetochiral anisotropy (eMChA), have attracted much attention for their importance to study quantum and spin-related phenomena. Indeed, they have permitted the exploration of topological surface states and charge-to-spin conversion processes in low-symmetry systems. Nevertheless, despite the inherent correlation between the symmetry of the material under examination and its non-linear transport characteristics, there is a lack of experimental demonstration to delve into this relationship and to unveil their microscopic mechanisms. Here, we study eMChA in chiral elemental Tellurium (Te) along different crystallographic directions, establishing the connection between the different eMChA components and the crystal symmetry of Te. We observed different longitudinal eMChA components with collinear current and magnetic field, demonstrating experimentally the radial angular momentum texture of Te. We also measured a transverse non-linear resistance which, as the longitudinal counterpart, scales bilinearly with current and magnetic fields, illustrating that they are different manifestations of the same effect. Finally, we study the scaling law of the eMChA, evidencing that extrinsic scattering from dynamic sources is the dominant microscopic mechanism. These findings underscore the efficacy of symmetry-based investigations in understanding and predicting non-linear transport phenomena, with potential applications in spintronics and energy harvesting.

cond-mat.mes-hall↗

arXiv2024

Efficient Terahertz Generation from CoPt-based Terahertz Emitters via Orbital-to-Charge Conversion

Orbitronics devices operate by manipulating orbitally-polarized currents. Recent studies have shown that these orbital currents can be excited by femtosecond laser pulses in ferromagnet as Ni and converted into ultrafast charge current via orbital-to-charge conversion. However, the terahertz emission from orbitronic terahertz emitter based on Ni is still much weaker than the typical spintronic terahertz emitter. Here, we report more efficient light-induced generation of orbital current from CoPt alloy and the orbitronic terahertz emission by CoPt/Cu/MgO shows terahertz radiation comparable to that of efficient spintronic terahertz emitters. By varying the concentration of CoPt alloy, the thickness of Cu, and the capping layer, we confirm that THz emission primarily originates from the orbital accumulation generated within CoPt, propagating through Cu and followed by the subsequent orbital-to-charge conversion from the inverse orbital Rashba-Edelstein effect at the Cu/MgO interface. This study provides strong evidence for the very efficient orbital current generation in CoPt alloy, paving the way to efficient orbital terahertz emitters.

cond-mat.mes-hall↗

arXiv2023

Electrical control of magnetism by electric field and current-induced torques

While early magnetic memory designs relied on magnetization switching by locally generated magnetic fields, key insights in condensed matter physics later suggested the possibility to do it electrically. In the 1990s, Slonczewzki and Berger formulated the concept of current-induced spin torques in magnetic multilayers through which a spin-polarized current may switch the magnetization of a ferromagnet. This discovery drove the development of spin-transfer-torque magnetic random-access memories (STT-MRAMs). More recent research unveiled spin-orbit-torques (SOTs) and will lead to a new generation of devices including SOT-MRAMs. Parallel to these advances, multiferroics and their magnetoelectric coupling experienced a renaissance, leading to novel device concepts for information and communication technology such as the MESO transistor. The story of the electrical control of magnetization is that of a dance between fundamental research (in spintronics, condensed matter physics, and materials science) and technology (MRAMs, MESO, microwave emitters, spin-diodes, skyrmion-based devices, components for neuromorphics, etc). This pas de deux led to major breakthroughs over the last decades (pure spin currents, magnetic skyrmions, spin-charge interconversion, etc). As a result, this field has propelled MRAMs into consumer electronics products but also fueled discoveries in adjacent research areas such as ferroelectrics or magnonics. Here, we cover recent advances in the control of magnetism by electric fields and by current-induced torques. We first review fundamental concepts in these two directions, then discuss their combination, and finally present various families of devices harnessing the electrical control of magnetic properties for various application fields. We conclude by giving perspectives in terms of both emerging fundamental physics concepts and new directions in materials science.

physics.app-ph↗

arXiv2023

Current manipulation of Giant tunneling altermagnetic resistance in collinear Antiferromagnetic RuO2/MgO/RuO2 sandwich structure

As an emerging non-volatile memory technology, magnetic random access memory (MRAM) has key features and advantages including non-volatility, high speed, endurance, low power consumption and radiation tolerance. Conventional MRAM utilizes magnetic tunnel junctions (MTJs), which consist of two ferromagnetic layers separated by an insulating tunnel barrier. The orientation of the magnetic layers represents the binary data (0 or 1), and electrical resistance changes depending on the relative orientation of these magnetic layers. Despite these advancements, the quest for a swifter, more stable magneto-resistive random-access memory paradigm persists. In this vein, we present a groundbreaking development: room-temperature antiferromagnetic tunnel junctions devoid of any net magnetic moment. Over 200% tunneling altermagnetic resistance (TAR) ratio was measured at RuO2 (110)/MgO/RuO2 (110)/W structure, which is achieved by changing the antiferromagnetic Neel vector of RuO2 with an ultralow current density 2 MA*cm-2.

physics.app-ph↗

arXiv2023

Odd non-linear conductivity under spatial inversion in chiral Tellurium

Electrical transport in non-centrosymmetric materials departs from the well-established phenomenological Ohm's law. Instead of a linear relation between current and electric field, a non-linear conductivity emerges along specific crystallographic directions. This non-linear transport is fundamentally related to the lack of spatial inversion symmetry. However, the experimental implications of an inversion symmetry operation on the non-linear conductivity remain to be explored. Here, we report on a large, non-linear conductivity in chiral Tellurium. By measuring samples with opposite handedness, we demonstrate that the non-linear transport is odd under spatial inversion. Furthermore, by applying an electrostatic gate, we modulate the non-linear output by a factor of 300, reaching the highest reported value excluding engineered heterostructures. Our results establish chiral Te as an ideal compound not just to study the fundamental interplay between crystal structure, symmetry operations and non-linear transport, but also to develop wireless rectifiers and energy-harvesting chiral devices.

cond-mat.mes-hall↗

arXiv2023

Spin-flop magnetoresistance in a collinear antiferromagnetic tunnel junction

Collinear antiferromagnetic (AFM) materials have unique promise of no stray fields, display ultrafast dynamics, and being robust against perturbation filed which motivates the extensive research of antiferromagnetic spintronics. However, the manipulation and detection of antiferromagnetic order remain formidable challenges. Here, we report the electrical detection of colinear antiferromagnetism in all-epitaxial RuO2/MgO/RuO2 three-terminal tunnel junctions (TJ) using spin-flop tunnel anisotropy magnetoresistance (TAMR). We measured a TAMR ratio of around 60% at room temperature, which arises between the parallel and perpendicular configurations of the adjacent collinear AFM state. Furthermore, we carried out angular dependent measurements using this AFM-TJ and showed that the magnitude of anisotropic longitudinal magnetoresistance in the AFM-TJ can be controlled by the direction of magnetic field. We also theoretically found that the colinear antiferromagnetic MTJ may produce a substantially large TAMR ratio as a result of the time-reversal, strong spin orbit coupling (SOC) characteristic of antiferromagnetic RuO2. Our work not only propels antiferromagnetic materials to the forefront of spintronic device innovation but also unveils a novel paradigm for electrically governed antiferromagnetic spintronics, auguring transformative advancements in high-speed, low-energy information devices.

physics.app-ph↗

arXiv2023

Orbitronics: Light-induced Orbit Currents in Terahertz Emission Experiments

Orbitronics is based on the use of orbit currents as information carriers. Up to now, orbit currents were created from the conversion of charge or spin currents, and inversely, they could be converted back to charge or spin currents. Here we demonstrate that orbit currents can also be generated by femtosecond light pulses on Ni. In multilayers associating Ni with oxides and nonmagnetic metals such as Cu, we detect the orbit currents by their conversion into charge currents and the resulting terahertz emission. We show that the orbit currents extraordinarily predominate the light-induced spin currents in Ni-based systems, whereas only spin currents can be detected with CoFeB-based systems. In addition, the analysis of the time delays of the terahertz pulses leads to relevant information on the velocity and propagation of orbit carriers. Our finding of light-induced orbit currents and our observation of their conversion into charge currents opens new avenues in orbitronics, including the development of orbitronic terahertz devices.

cond-mat.mes-hall↗

arXiv2023

Driving skyrmions in flow regime in synthetic ferrimagnets

Despite significant advances in the last decade regarding the room temperature stabilization of skyrmions or their current induced dynamics, the impact of local material inhomogeneities still remains an important issue that impedes to reach the regime of steady state motion of these spin textures. Here, we study the spin-torque driven motion of skyrmions in synthetic ferrimagnetic multilayers with the aim of achieving high mobility and reduced skyrmion Hall effect. We consider Pt|Co|Tb multilayers of various thicknesses with antiferromagnetic coupling between the Co and Tb magnetization. The increase of Tb thickness in the multilayers allows to reduce the total magnetic moment and increases the spin-orbit torques allowing to reach velocities up to 400 m.s-1 for skyrmions with diameters of about 160 nm. We demonstrate that due to reduced skyrmion Hall effect, combined with the edge repulsion of the magnetic track making the skyrmions moving along the track without any transverse deflection. Further, by comparing the field-induced domain wall motion and current-induced skyrmion motion, we demonstrate that the skyrmions at the largest current densities present all the characteristics of a dynamical flow regime.

cond-mat.mtrl-sci↗

arXiv2023

From Early Theories of Dzyaloshinskii-Moriya Interactions in Metallic Systems to Today's Novel Roads

Since the early 1960's, the discovery of Dzyaloshinskii-Moriya interaction (DMI) helped to explain the physical mechanisms behind certain magnetic phenomena, such as net moment in antiferromagnets, or enhanced anisotropy field from heavy metals impurity in dilute Cu:Mn alloy. Since the researchers unveil the key role that DMI plays in stabilizing chiral Neel type magnetic domain wall and magnetic skyrmions, the studies on DMI have received growing interest. Governed by spin-orbit coupling (SOC) and various types of inversion symmetry breaking (ISB) in magnetic systems, DMI drives the forming of distinct morphologies of magnetic skyrmions. Our aim is to briefly introduce the research history of DMI and its significance in the field of modern spintronics.

cond-mat.mtrl-sci↗

arXiv2023

Field-free switching of perpendicular magnetization in an ultrathin epitaxial magnetic insulator

For energy efficient and fast magnetic memories, switching of perpendicular magnetization by the spin-orbit torque (SOT) appears as a very promising solution, even more using magnetic insulators that suppress electrical shunting. This SOT switching generally requires the assistance of an in-plane magnetic field to break the symmetry. Here, we present experiments demonstrating the field-free SOT switching of perpendicularly magnetized layers of the thulium iron garnet (Tm_{3}Fe_{5}O_{12}) magnetic insulator. The polarity of the switching loops, clockwise (CW) or counter-clockwise (CCW), is determined by the direction of the initial current pulses, in contrast with field-assisted switchings in which this polarity is controlled by the direction of the field. After an independent determination of Dzyaloshinskii-Moriya interaction (DMI), we relate the field free switching to the interplay of SOT and DMI and the polarity of the loops to the imprint of a N\'eel domain wall induced by the first pulse, in agreement with Kerr imaging. Our observation and interpretation of field-free electrical switching of a magnetic insulator is an important milestone for future low power spintronic devices.

physics.app-ph↗

arXiv2022

Gradient-induced Dzyaloshinskii-Moriya interaction

The Dzyaloshinskii-Moriya interaction (DMI) that arises in the magnetic systems with broken inversion symmetry plays an essential role in topological spintronics. Here, by means of atomistic spin calculations, we study an intriguing type of DMI (g-DMI) that emerges in the films with composition gradient. We show that both the strength and chirality of g-DMI can be controlled by the composition gradient even in the disordered system. The layer-resolved analysis of g-DMI unveils its additive nature inside the bulk layers and clarifies the linear thickness dependence of g-DMI observed in experiments. Furthermore, we demonstrate the g-DMI induced chiral magnetic structures, such as spin spirals and skyrmions, and the g-DMI driven field-free spin-orbit torque (SOT) switching, both of which are crucial towards practical device application. These results elucidate the underlying mechanisms of g-DMI and open up a new way to engineer the topological magnetic textures.

cond-mat.mtrl-sci↗

arXiv2022

Inverse Orbital Hall Effect Discovered from Light-Induced Terahertz Emission

Recent progress in orbitronics reveals the possibility of using orbit current as an information carrier. The interconversion between orbit currents and charge currents is crucial for orbit information processing. Although orbit currents can be created from charge currents via the orbital Hall effect, the conversion from orbit currents into charge currents has been observed only in very few systems due to the lack of a reliable orbit current source and the disturbance of the omnipresent inverse spin Hall effect. In this study, we show that ultrafast pulses of orbit current can be generated in Ni layers by femtosecond laser pulses. We demonstrate that, by injecting such orbit current pulses into nonmagnetic metals, a transient charge current is induced and emits terahertz electromagnetic pulses. The nonmagnetic metal layer acts as a converter of the orbit current into the charge current. The discovery of the generation and conversion of light-induced orbit current opens a new route for developing future orbitronic devices.

cond-mat.mes-hall↗

arXiv2022

Field-free spin orbit torque switching of synthetic antiferromagnet through interlayer Dzyaloshinskii-Moriya interaction

Perpendicular synthetic antiferromagnets (SAFs) are of interest for the next generation ultrafast, high density spintronic memory and logic devices. However, to energy efficiently operate their magnetic order by current-induced spin orbit torques (SOTs), an unfavored high external field is conventionally required to break the symmetry. Here, we theoretically and experimentally demonstrate the field-free SOT switching of a perpendicular SAF through the introduction of interlayer Dzyaloshinskii-Moriya interaction (DMI). By macro-spin simulation, we show that the speed of field-free switching increases with the in-plane mirror asymmetry of injected spins. We experimentally observe the existence of interlayer DMI in our SAF sample by an azimuthal angular dependent anomalous Hall measurement. Field-free switching is accomplished in such a sample and the strength of the effective switching field demonstrates its origin from interlayer DMI. Our results provide a new strategy for SAF based high performance SOT devices.

physics.app-ph↗

arXiv2022

Multiferroic materials based on transition-metal dichalcogenides: Potential platform for reversible control of Dzyaloshinskii-Moriya interaction and skyrmion via electric field

Exploring novel two-dimensional multiferroic materials that can realize electric-field control of two-dimensional magnetism has become an emerging topic in spintronics. Using first-principles calculations, we demonstrate that non-metallic bilayer transition metal dichalcogenides (TMDs) can be an ideal platform for building multiferroics by intercalated magnetic atoms. Moreover, we unveil that with Co intercalated bilayer MoS2, Co(MoS2)2, two energetic degenerate states with opposite chirality of Dzyaloshinskii-Moriya interaction (DMI) are the ground states, indicating electric-field control of the chirality of topologic magnetism such as skyrmions can be realized in this type of materials by reversing the electric polarization. These findings pave the way for electric-field control of topological magnetism in two-dimensional multiferroics with intrinsic magnetoelectric coupling.

cond-mat.mtrl-sci↗