arXiv subjects

Sajid Husain

Publications and source records attributed to Sajid Husain.

At least 19 recordsLinked to original sources

arXiv2026

Electric field controlled spin transport in a topological insulator interfaced with a ferroelectric antiferromagnet

Topological insulators have been explored extensively for spin-charge interconversion via magnetic interfaces, yet the true response of their spin-charge conversion, particularly in the absence of an external magnetic field, remains to be studied. Here, we report electric-field control of spin-charge conversion in the topological insulator Bi$_2$Te$_3$ with the antiferromagnetic multiferroic BiFeO$_3$, employing a nonlocal spin transport device. A systematic thickness dependence of the spin transport across the interface between Bi$_2$Te$_3$ and BiFeO$_3$ reveals a signature of topological surface-state-dominated spin transport in the bilayer system. The spin-charge conversion remains robust for thicknesses above 10 nm but falls rapidly with reducing thickness and vanishes at 5 nm. This is consistent with the hybridization-induced emergence of a trivial insulating phase, which is supported by the coherency factor estimated from the magnetoconductance of Bi$_2$Te$_3$. These results establish that spin-momentum-locked surface states dominate interfacial spin transport in the decoupled regime. Beyond presenting efficient spin-charge interconversion at an entirely insulating magnetic interface, this work also highlights sputter-deposited Bi$_2$Te$_3$ as a high-quality and scalable platform for integrating quantum materials into devices. The nonlocal spin transport approach presented here provides a simple and direct evidence of spin-charge conversion and opens an efficient and practical pathway toward designing energy-efficient spin-based devices.

cond-mat.mes-hall↗

arXiv2026

Revealing buried ferroelectric topologies by depth-resolved electron diffraction imaging

Nanoscale topological polar textures promise new functionalities for ferroelectric memories and logic, yet their three-dimensional structure and mesoscale organization remain experimentally inaccessible. Here we introduce depth-resolved electron diffraction imaging (DREDI), a fast, non-destructive, method that maps polarization with <50 nm lateral and <10 nm depth sensitivity within fraction of a second. Its high acquisition speed enables the first continuous polarization mapping across six orders of magnitude in length scale, from nanometers to millimeters. Using epitaxial BiFeO3 films, DREDI reveals a hidden depth evolution of polar textures: surface 71-degree stripes evolve into subsurface flux-closure vortices that bifurcate into three-fold vertices near the bottom interface. Cross-sectional multi-slice electron ptychography and phase-field modeling confirm these buried configurations and attribute them to strain heterogeneity and ferroelastic twinning in the SrRuO3 electrode. Large-area analysis further shows that vertex-like frustration forms a mesoscale percolating network above a critical length scale of 4 um. DREDI enables real-time, volumetric studies of buried topological textures in ferroic nanomaterials.

cond-mat.mtrl-sci↗

arXiv2026

Spatially modulated morphotropic phase boundaries in a compressively strained multiferroic thin film

The coexisting rhombohedral-like (R', MA) and tetragonal-like (T', MC) monoclinic phases in compressively strained bismuth ferrite thin films exhibit exceptional piezoelectric and magnetic properties. While previous studies have largely focused on probing the morphotropic phase boundaries (MPBs) comprising ordered R'/T' twins, their self-organizing structures remain not fully explored. Here, we observed two types of interphase boundaries in a 60 nm-thick BiFeO3 film epitaxially grown on a LaAlO3 substrate by employing multi-modal diffraction-based electron microscopy. First, the flat MPBs form lines extending >1 mm, and repeat almost every ~20 um. Additionally, we uncover a new type of phase boundary with zig-zag regions of alternating R'/R' and T'/T' twin domains. Cross-sectional multislice electron ptychography confirms the atomic-scale polarization rotation across the MPB, with out-of-plane strain varying >15%. Plan-view electron backscatter diffraction reveals the lattice disclination of ~1.5-degrees across the zig-zag interphase boundaries, while having >2.5 degrees within the MPB. Phase-field modeling suggests that the formation of zig-zag phase boundaries arises from balancing between Landau and elastic energies. We speculate that such well-ordered interphase boundaries are associated with mesoscale in-plane strain modulations, thus providing a way to engineer and harness their properties for potential device applications.

cond-mat.mtrl-sci↗

arXiv2026

Mechanical Control of Polar Order

BiFeO3 is a model multiferroic in which the ferroelectric polarization is coupled to ferroelastic lattice distortions, yet deterministic control of its domain structure remains limited by high switching fields and competing polarization variants. Here, we identify a mechanically assisted polarization switching pathway in epitaxial BiFeO3 thin films that fundamentally alters the switching energetics. Using just out-of-plane electric fields, polarization reversal requires voltages of approximately 4 V and stabilizes coexisting polarization states. In contrast, when mechanical pressure is applied concurrently, the coercive voltage can be significantly reduced (even to 0V), resulting in spontaneous switching. Piezoresponse force microscopy measurements reveal that applied mechanical pressure suppresses ferroelastic domain competition, indicating a decrease in the required electrical energy barrier associated with polarization rotation and domain wall motion. These results demonstrate that stress acts as an active thermodynamic control parameter, enabling access to switching pathways that are inaccessible under only an electric field. By directly coupling lattice distortions to polarization reversal, mechanically assisted switching provides a general framework for controlling coupled order parameters in multiferroic oxides, which can be directly applied in the device-level architecture, where a small mechanical pressure can help in achieving lower switching energy of ferroelectric polarization. This work advances the fundamental understanding of electromechanical coupling in complex ferroics and establishes mechanical energy as a powerful tool for probing and manipulating ferroelastic ferroelectric interactions.

cond-mat.mtrl-sci↗

arXiv2026

A Magnon-Based Electric Field Controlled Magnetoelectric Device for Energy-Efficient Logic-in-Memory

We demonstrate a non-volatile magnetoelectric magnonic memory (MEMM) that enables fully electrical write/read via direct magnon-driven sensing in an insulating antiferromagnet. A fabricated SrIrO3/La-BiFeO3/SrIrO3 trilayer exhibits sub-100 ps switching, a remnant polarization of 20 uC/cm2, and a readout voltage contrast close to 1mV between high and low-resistance states. To connect device physics to circuit behavior, we develop and experimentally validate a compact circuit model that captures spin Hall injection and spin transport. Simulations with optimized material parameters predict output voltages > 100mV, enabling cascading without external amplification. Using this framework, we design MEMM-based memory and logic blocks, including a 1T1R array, two inverter implementations (complementary two-device and single-device), and a three-input majority gate, and evaluate deep-pipelined operation. The model projects switching energies down to 1 aJ per operation and logic propagation delays of 30-60 ps, indicating MEMM as a promising platform for energy-constrained, high throughput computing.

cond-mat.mtrl-sci↗

arXiv2026

Anisotropic magnon transport in an antiferromagnetic trilayer heterostructure: is BiFeO$_3$ an altermagnet?

Magnons provide a route to ultra-fast transport and non-destructive readout of spin-based information transfer. Here, we report magnon transport and its emergent anisotropic nature in BiFeO$_3$ layers confined between ultrathin layers of the antiferromagnet LaFeO$_3$. Due to the confined state, BiFeO$_3$ serves as an efficient magnon transmission channel as well as a magnetoelectric knob by which to control the stack by means of an electric field. We discuss the mechanism of the anisotropic spin transport based on the interaction between the antiferromagnetic order and the electric field. This allows us to manipulate and amplify the spin transport in such a confined geometry. Furthermore, lower crystal symmetric and suppression of the spin cycloid in ultrathin BiFeO$_3$ stabilizes a non-trivial antiferromagnetic state exhibiting symmetry-protected spin-split bands that provide the non-trivial sign inversion of the spin current, which is a characteristic of an altermagnet. This work provides an understanding of the anisotropic spin transport in complex antiferromagnetic heterostructures where ferroelectricity and altermagnetism coexist, paving the way for a new route to realize electric-field control of a novel state of magnetism.

cond-mat.mes-hall↗

arXiv2025

Revealing Atomic-Scale Switching Pathways in van der Waals Ferroelectrics

Two-dimensional van der Waals (vdW) materials hold the potential for ultra-scaled ferroelectric (FE) devices due to their silicon compatibility and robust polarization down to atomic scale. However, the inherently weak vdW interactions enable facile sliding between layers, introducing complexities beyond those encountered in conventional ferroelectric materials and presenting significant challenges in uncovering intricate switching pathways. Here, we combine atomic-resolution imaging under in-situ electrical biasing conditions with first-principles calculations to unravel the atomic-scale switching mechanisms in SnSe, a vdW group-IV monochalcogenide. Our results uncover the coexistence of a consecutive 90 degrees switching pathway and a direct 180 degrees switching pathway from antiferroelectric (AFE) to FE order in this vdW system. Atomic-scale investigations and strain analysis reveal that the switching processes simultaneously induce interlayer sliding and compressive strain, while the lattice remains coherent despite the presence of multidomain structures. These findings elucidate vdW ferroelectric switching dynamics at atomic scale and lay the foundation for the rational design of 2D ferroelectric nanodevices.

cond-mat.mtrl-sci↗

arXiv2025

Low-energy domain wall racetracks with multiferroic topologies

Conventional racetrack memories move information by pushing magnetic domain walls or other spin textures with spin-polarized currents, but the accompanying Joule heating inflates their energy budget and can hamper scaling. Here we present a voltage-controlled, magnetoelectric racetrack in which transverse electric fields translate coupled ferroelectric-antiferromagnetic walls along BiFeO3 nanostrips at room temperature. Because no charge traverses the track, the switching dissipates orders of magnitude less energy than the most efficient spin-torque devices with more favourable scaling, making the scheme significantly more attractive at the nanoscale. We further uncover noncollinear topological magnetoelectric textures that emerge at domain walls in BiFeO3, where the nature of these topologies influences their stability upon translation. Among these are polar bi-merons and polar vertices magnetoelectrically coupled with magnetic cycloid disclinations and previously unobserved, topological magnetic cycloid twist topologies. We observe domain wall velocities of at least kilometres per second - matching or surpassing the fastest ferrimagnetic and antiferromagnetic racetracks and approaching the acoustic-phonon limit of BiFeO3 - while preserving these topologies over tens of micrometres. The resulting high velocity, low-energy racetrack delivers nanosecond access times without the thermal overhead of current-driven schemes, charting a path toward dense, ultralow-power racetrack devices which rely on spin texture translation.

cond-mat.mtrl-sci↗

arXiv2025

Colossal enhancement of spin transmission through magnon confinement in an antiferromagnet

Since Felix Bloch's introduction of the concept of spin waves in 1930, magnons (the quanta of spin waves) have been extensively studied in a range of materials for spintronics, particularly for non-volatile logic-in-memory devices. Controlling magnons in conventional antiferromagnets and harnessing them in practical applications, however, remains a challenge. In this letter, we demonstrate highly efficient magnon transport in an LaFeO$_3$/BiFeO$_3$/LaFeO$_3$ all-antiferromagnetic system which can be controlled electrically, making it highly desirable for energy-efficient computation. Leveraging spin-orbit-driven spin-charge transduction, we demonstrate that this material architecture permits magnon confinement in ultrathin antiferromagnets, enhancing the output voltage generated by magnon transport by several orders of magnitude, which provides a pathway to enable magnetoelectric memory and logic functionalities. Additionally, its non-volatility enables ultralow-power logic-in-memory processing, where magnonic devices can be efficiently reconfigured via electrically controlled magnon spin currents within magnetoelectric channels.

cond-mat.mtrl-sci↗

arXiv2025

Magnon thermal conductivity in multiferroics with spin cycloids

Multiferroic materials, characterized by the occurrence of two or more ferroic properties, hold potential in future technological applications and also exhibit intriguing phenomena caused by the interplay of multiple orders. One such example is the formation of spin cycloid structures within multiferroic materials, which we investigate in this work by focusing on their magnon excitations and transport based on a general multiferroic Hamiltonian with an antiferromagnetic order. More specifically, we identify the ground state and explore the dynamics of magnon modes, revealing distinct in-plane and out-of-plane modes with anisotropic dispersion relations.The magnon modes include a massless excitation, known as the Goldstone boson, originating from the spontaneous breaking of the translational symmetry by the formation of the cycloid structures. By employing the Boltzmann transport formalism, the magnonic thermal conductivity with spin cycloids and low-temperature anisotropic behaviors is discussed. This work provides pathways to envision the spin-textured multiferroics, which may serve as a fertile ground to look for novel thermal and spin transport with the rich interplay of quasiparticles such as magnons and phonons.

cond-mat.mtrl-sci↗

arXiv2024

Symmetry-based phenomenological model for magnon transport in a multiferroic

Magnons carriers of spin information can be controlled by electric fields in the multiferroic BiFeO$_3$ (BFO), a milestone that brings magnons closer to application in future devices. The origin of magnon-spin currents in BFO, however, is not fully understood due to BFO's complicated magnetic texture. In this letter, we present a phenomenological model to elucidate the existence of magnon spin currents in generalized multiferroics by examining the symmetries inherent to their magnetic and polar structures. This model is grounded in experimental data obtained from BFO and its derivatives, which informs the symmetry operations and resultant magnon behavior. By doing so, we address the issue of symmetry-allowed, switchable magnon spin transport in multiferroics, thereby establishing a critical framework for comprehending magnon transport within complex magnetic textures.

cond-mat.mtrl-sci↗

arXiv2024

Morphogenesis of Spin Cycloids in a Non-collinear Antiferromagnet

Pattern formation in spin systems with continuous-rotational symmetry (CRS) provides a powerful platform to study emergent complex magnetic phases and topological defects in condensed-matter physics. However, its understanding and correlation with unconventional magnetic order along with high-resolution nanoscale imaging is challenging. Here, we employ scanning NV magnetometry to unveil the morphogenesis of spin cycloids at both the local and global scales within a single ferroelectric domain of (111)-oriented BiFeO$_3$ (which is a non-collinear antiferromagnet), resulting in formation of a glassy labyrinthine pattern. We find that the domains of locally oriented cycloids are interconnected by an array of topological defects and exhibit isotropic energy landscape predicted by first-principles calculations. We propose that the CRS of spin-cycloid propagation directions within the (111) drives the formation of the labyrinthine pattern and the associated topological defects such as antiferromagnetic skyrmions. Unexpectedly, reversing the as-grown ferroelectric polarization from [$\bar{1}$$\bar{1}$$\bar{1}$] to [111] induces a magnetic phase transition, destroying the labyrinthine pattern and producing a deterministic non-volatile non cycloidal, uniformly magnetized state. These findings highlight that (111)-oriented BiFeO$_3$ is not only important for studying the fascinating subject of pattern formation but could also be utilized as an ideal platform for integrating novel topological defects in the field of antiferromagnetic spintronics.

cond-mat.mtrl-sci↗

arXiv2024

Non-volatile spin transport in a single domain multiferroic

Antiferromagnets have attracted significant attention in the field of magnonics, as promising candidates for ultralow-energy carriers for information transfer for future computing. The role of crystalline orientation distribution on magnon transport has received very little attention. In multiferroics such as BiFeO$_3$ the coupling between antiferromagnetic and polar order imposes yet another boundary condition on spin transport. Thus, understanding the fundamentals of spin transport in such systems requires a single domain, a single crystal. We show that through Lanthanum(La) substitution, a single ferroelectric domain can be engineered with a stable, single-variant spin cycloid, controllable by an electric field. The spin transport in such a single domain displays a strong anisotropy, arising from the underlying spin cycloid lattice. Our work shows a pathway to understand the fundamental origins of spin transport in such a single domain multiferroic.

cond-mat.mtrl-sci↗

arXiv2024

Designed spin-texture-lattice to control anisotropic magnon transport in antiferromagnets

Spin waves in magnetic materials are promising information carriers for future computing technologies due to their ultra-low energy dissipation and long coherence length. Antiferromagnets are strong candidate materials due, in part, to their stability to external fields and larger group velocities. Multiferroic aniferromagnets, such as BiFeO$_3$ (BFO), have an additional degree of freedom stemming from magnetoelectric coupling, allowing for control of the magnetic structure, and thus spin waves, with electric field. Unfortunately, spin-wave propagation in BFO is not well understood due to the complexity of the magnetic structure. In this work, we explore long-range spin transport within an epitaxially engineered, electrically tunable, one-dimensional (1D) magnonic crystal. We discover a striking anisotropy in the spin transport parallel and perpendicular to the 1D crystal axis. Multiscale theory and simulation suggests that this preferential magnon conduction emerges from a combination of a population imbalance in its dispersion, as well as anisotropic structural scattering. This work provides a pathway to electrically-reconfigurable magnonic crystals in antiferromagnets.

cond-mat.mtrl-sci↗

arXiv2023

Persistent anisotropy of the spin cycloid in BiFeO3 through ferroelectric switching

A key challenge in antiferromagnetic spintronics is the control of spin configuration on nanometer scales applicable to solid-state technologies. Bismuth ferrite (BiFeO3) is a multiferroic material that exhibits both ferroelectricity and canted antiferromagnetism at room temperature, making it a unique candidate in the development of electric-field controllable magnetic devices. The magnetic moments in BiFeO3 are arranged into a spin cycloid, resulting in unique magnetic properties which are tied to the ferroelectric order. Previous understanding of this coupling has relied on average, mesoscale measurements to infer behavior. Using nitrogen vacancy-based diamond magnetometry, we show that the spin cycloid can be deterministically controlled with an electric field. The energy landscape of the cycloid is shaped by both the ferroelectric degree of freedom and strain-induced anisotropy, restricting the magnetization changes to specific ferroelectric switching events. This study provides understanding of the antiferromagnetic texture in BiFeO3 and paves new avenues for designing magnetic textures and spintronic devices.

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 Néel 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↗

arXiv2021

Giant spin-orbit torque efficiency in all-epitaxial heterostructures

A large anti-damping spin-obit torque (SOT) efficiency in magnetic heterostructures is a prerequisite to realize energy efficient spin torque based magnetic memories and logic devices. The efficiency can be characterized in terms of the spin-orbit fields generated by anti-damping torques when an electric current is passed through the non-magnetic layer. We report a giant spin-orbit field of 48.96 (27.50) mT at an applied current density of 1 MAcm-2 in beta-W interfaced Co60Fe40 (Ni81Fe19)/TiN epitaxial structures due to an anti-damping like torque, which results in a magnetization auto-oscillation current density as low as 1.68(3.27) MAcm-2. The spin-orbit field value increases with decrease of beta-W layer thickness, which affirms that epitaxial surface states are responsible for the extraordinary large efficiency. SOT induced energy efficient in-plane magnetization switching in large 20x100 um2 structures has been demonstrated by Kerr microscopy and the findings are supported by results from micromagnetic simulations. The observed giant SOT efficiencies in the studied all-epitaxial heterostructures are comparable to values reported for topological insulators. These results confirm that by utilizing epitaxial material combinations an extraordinary large SOT efficiency can be achieved using semiconducting industry compatible 5d heavy metals, which provides immediate solutions for the realization of energy efficient spin-logic devices.

cond-mat.mtrl-sci↗

arXiv2021

Co$_2$FeAl full Heusler compound based spintronic terahertz emitter

To achieve a large terahertz (THz) amplitude from a spintronic THz emitter (STE), materials with 100\% spin polarisation such as Co-based Heusler compounds as the ferromagnetic layer are required. However, these compounds are known to loose their half-metallicity in the ultrathin film regime, as it is difficult to achieve L2$_1$ ordering, which has become a bottleneck for the film growth. Here, the successful deposition using room temperature DC sputtering of the L2$_1$ and B2 ordered phases of the Co$_2$FeAl full Heusler compound is reported. Co$_2$FeAl is used as ferromagnetic layer together with highly orientated Pt as non-ferromagnetic layer in the Co$_2$FeAl/Pt STE, where an MgO(10 nm) seed layer plays an important role to achieve the L2$_1$ and B2 ordering of Co$_2$FeAl. The generation of THz radiation in the CFA/Pt STE is presented, which has a bandwidth in the range of 0.1-4 THz. The THz electric field amplitude is optimized with respect to thickness, orientation, and growth parameters using a thickness dependent model considering the optically induced spin current, superdiffusive spin current, inverse spin Hall effect and the attenuation of THz radiation in the layers. This study, based on the full Heusler Co$_2$FeAl compound opens up a plethora possibilities in STE research involving full Heusler compounds.

cond-mat.mtrl-sci↗