arXiv subjects

Mohamed Elekhtiar

Publications and source records attributed to Mohamed Elekhtiar.

8 recordsLinked to original sources

arXiv2026

Effects of Band Symmetry on Spin-Dependent Transport in Noncollinear Antiferromagnetic Tunnel Junctions

Antiferromagnetic tunnel junctions (AFMTJs) can exhibit large tunneling magnetoresistance (TMR), making them promising candidates for ultrafast and field-robust spintronic devices. Here, we elucidate the role of band symmetry in governing spin-dependent transport in AFMTJs. Using first-principles density-functional theory combined with quantum-transport calculations, we investigate Mn3NiN/LaAlO3/Mn3NiN (001) junctions based on the noncollinear $Γ_{4g}$ antiferromagnetic phase of Mn3NiN. Although Mn3NiN exhibits a large momentum-dependent spin polarization due to broken $PT$ symmetry, we show that the tunneling conductance is critically controlled by band symmetry of the electrode Bloch states and their symmetry-selective coupling to evanescent states in the LaAlO3 barrier. Orbital-symmetry selection rules suppress interband transmission in the parallel configuration, whereas the antiparallel configuration enables symmetry-compatible interband tunneling along the diagonal directions of the two-dimensional Brillouin zone. These additional transmission channels enhance the antiparallel conductance and reduce the TMR relative to predictions based solely on spin polarization. Nevertheless, the TMR remains exceptionally large, exceeding 2000%, while band symmetry controls the attainable magnitude of TMR in AFMTJs. Our results establish band-symmetry filtering as an essential ingredient of spin-dependent tunneling in AFMTJs.

cond-mat.mtrl-sci↗

arXiv2026

Exchange Frustration and Topological Magnetism in Electrostatically Doped SrRuO3

Magnetism in transition-metal systems emerges from exchange interactions that depend sensitively on carrier density. Yet leveraging this sensitivity to deliberately engineer exchange frustration and associated topological spin textures remains largely unexplored. Here, combining first-principles calculations with atomistic Monte Carlo simulations, we demonstrate that ferroelectric polarization enables electrostatic control of exchange frustration in the itinerant ferromagnet SrRuO3. We show that electrostatic hole doping renormalizes competing exchange interactions, driving SrRuO3 away from its bulk ferromagnetic ground state toward frustrated regimes, whereas electron doping largely preserves ferromagnetism. At BaTiO3/SrRuO3 interfaces, polarization-induced charge depletion modulates layer dependent exchange couplings, enhancing competition among J1, J2 and J3. The resulting exchange frustration stabilizes a sequence of magnetic phases as a function of thickness and applied magnetic field, including stripe and spiral states, topological meron and bimeron textures, and diverse skyrmionic objects. A minimal spin model identifies exchange frustration as the primary control parameter governing these crossovers, with magnetic anisotropy, Dzyaloshinskii-Moriya interaction, and external field selecting the emergent topology. Our results establish electrostatic doping as a route to engineer frustrated and topological magnetism in itinerant oxide metals.

cond-mat.mtrl-sci↗

arXiv2025

Competing Antiferromagnetic Phases in Multiferroic Wurtzite Transition-Metal Chalcogenides

Antiferromagnetic (AFM) spintronics offers a pathway toward electrically controllable spin-based devices beyond ferromagnets. Here, we identify wurtzite MnX (X = S, Se, Te) as a family of multiferroic materials hosting competing AFM phases, including altermagnetic, where nonrelativistic spin splitting can be controlled by ferroelectric polarization. Using density-functional theory and atomistic spin-model calculations, we show that all pristine MnX compounds stabilize a stripe type collinear AFM ground state, contrary to earlier predictions of an altermagnetic ground state, with the magnetic order governed by frustrated Heisenberg and biquadratic exchange interactions. We further demonstrate that Cr doping drives a transition to an A-type AFM phase that breaks Kramers spin degeneracy and realizes a g-wave altermagnetic state with large nonrelativistic spin splitting near the Fermi level. Importantly, this spin splitting can be deterministically reversed by polarization switching, enabling electric-field control of altermagnetic electronic structure without reorienting the Neel vector or relying on spin-orbit coupling. The close energetic proximity of the stripe AFM to a noncollinear all-in-all-out configuration indicates that wurtzite MnX lies near a topological magnetic phase with finite scalar spin chirality, which may be stabilized by modest perturbations such as temperature, strain or chemical tuning. The distinct magnetic phases exhibit symmetry selective linear and non-linear Hall responses, providing direct transport signatures of altermagnetism and polarization control. Together, these results establish doped wurtzite MnX as a promising platform for altermagnet-ferroelectric multiferroics and electrically AFM spintronics.

cond-mat.mtrl-sci↗

arXiv2025

Octupole-driven spin torque switching of antiferromagnetic tunnel junctions

Magnetic tunnel junctions (MTJs) based on ferromagnets are canonical devices in spintronics, with wide-ranging applications in data storage, computing, and sensing. They simultaneously exhibit mechanisms for electrical detection and control of magnetic order through the tunneling magnetoresistance (TMR) and spin-transfer torque (STT) effects, respectively. It was long assumed that neither of these effects could be sizeable in all-antiferromagnetic tunnel junctions (AATJs), since they exhibit no net magnetization. Recently, however, it was shown that AATJs based on chiral antiferromagnets do exhibit TMR due to their non-relativistic momentum-dependent spin polarization and cluster magnetic octupole moment (CMO), which are manifestations of their spin-split band structure. However, the reciprocal effect, i.e., the antiferromagnetic counterpart of STT, has been assumed non-existent due to the total electric current being spin-neutral. Here, we report nanoscale AATJs exhibiting this reciprocal effect, which we term octupole-driven spin-transfer torque (OTT). We demonstrate current-induced OTT switching of PtMn3|MgO|PtMn3 AATJs, exhibiting a TMR value of 363% at room temperature and switching current densities of the order of 10 MA/cm2. Our theoretical modeling explains the origin of OTT in terms of the imbalance between intra- and inter-sublattice spin currents across the AATJ, and equivalently, in terms of the non-zero net cluster octupole polarization of each PtMn3 layer. This work establishes a new materials platform for antiferromagnetic spintronics and provides a pathway towards deeply scaled magnetic memory and room-temperature terahertz technologies.

cond-mat.mtrl-sci↗

arXiv2024

Prediction of polarization vortices, charge modulation, flat bands, and moiré magnetism in twisted oxide bilayers

The recent surge of interest in moiré superlattices of twisted van der Waals compounds has spotlighted the emergence of unconventional superconductivity and novel electronic phases. However, the range of moiré phenomena can be dramatically expanded by incorporating complex oxide materials into twisted heterostructures. In this study, motivated by the recent breakthroughs in synthesis of free-standing oxide membranes, we explore the emergent structural and electronic properties of twisted oxide bilayers. We focus on the classic perovskite oxide, SrTiO3, and design SrTiO3 bilayers with a relative twist between the individual layers. Using density functional theory calculations, we predict the appearance of vortex-antivortex polarization patterns at the interface of the SrTiO3 bilayers driven by twist. We also predict charge modulation of the interfacial Ti ions induced by varying local coordination which follow the moiré pattern. Furthermore, we forecast the emergence of flat bands at large twist angles and the associated localized electronic states with moiré-periodic charge density, originating from the interlayer bonding effects resulting in the formation of dangling bonds. Finally, we predict that hole doping induces unconventional d0 magnetism in otherwise nonmagnetic SrTiO3, driven by the exchange splitting of the high-density O-p bands and producing the spin density with moiré periodicity. These results demonstrate a broad landscape of emergent phenomena which may occur in moiré-engineered oxide heterostructures showing far-reaching perspectives of these material systems for further fundamental studies and potential applications.

cond-mat.mtrl-sci↗

arXiv2024

Nearly perfect spin polarization of noncollinear antiferromagnets

Ferromagnets with high spin polarization are known to be valuable for spintronics--a research field that exploits the spin degree of freedom in information technologies. Recently, antiferromagnets have emerged as promising alternative materials for spintronics due to their stability against magnetic perturbations, absence of stray fields, and ultrafast dynamics. For antiferromagnets,however, the concept of spin polarization and its relevance to the measured electrical response are elusive due to nominally zero net magnetization.Here, we define an effective momentum-dependent spin polarization and reveal an unexpected property of many noncollinear antiferromagnets to exhibit nearly 100% spin polarization in a broad area of the Fermi surface. This property leads to the emergence of an extraordinary tunneling magnetoresistance (ETMR) effect in antiferromagnetic tunnel junctions (AFMTJs). As a representative example, we predict that a noncollinear antiferromagnet Mn$_{3}$GaN exhibits nearly 100% spin-polarized states that can efficiently tunnel through low-decay-rate evanescent states of perovskite oxide SrTiO$_{3}$ resulting in ETMR as large as $10^{4}$%. Our results uncover hidden functionality of material systems with noncollinear spin textures and open new perspectives for spintronics.

cond-mat.mtrl-sci↗

arXiv2024

Direct imaging and control of Berry curvature in noncollinear antiferromagnetic single-crystal thin films

The discovery of the intrinsic anomalous Hall effect (AHE) in noncollinear antiferromagnets where transverse Hall voltage emerges without magnetic field, has opened a plethora of promising opportunities in antiferromagnetic devices. The key challenges limiting their full potential are (1) high-quality epitaxial thin-film growth and (2) the understanding of Berry curvature domain physics. Here, we focus on a noncollinear antiperovskite antiferromagnet Mn3NiN as a model system, successfully grown as a single-crystal epitaxial thin film. Combining multiple experiments supported by theoretical calculations, we probe the Berry curvature associated with antiferromagnetic {\Gamma}4g domains in Mn3NiN and its strong connection to an AHE. We directly image the intrinsic Berry curvature with high-resolution Sagnac microscopy, controlling spatial distribution and dynamics by varying temperature and applied magnetic fields. We discover that the {\Gamma}4g domains are switchable near the N\'eel transition, but become frozen and unresponsive to external stimuli at low temperature. This behavior enables the tuning of Berry-curvature driven AHE and magneto-optic Kerr effect responses through controlled experimental conditions. Our findings provide critical advancement of the fundamental understanding and wide tunability of Berry curvature in noncollinear antiferromagnets important for realization in potential spintronic applications.

cond-mat.mtrl-sci↗

arXiv2023

Majorana bound states in d-wave superconductor planar Josephson junction

We study phase-controlled planar Josephson junctions comprising a two-dimensional electron gas with strong spin-orbit coupling and d-wave superconductors, which have an advantage of high critical temperature. We show that a region between the two superconductors can be tuned into a topological state by the in-plane Zeeman field, and can host Majorana bound states. The phase diagram as a function of the Zeeman field, chemical potential, and the phase difference between superconductors exhibits the appearance of Majorana bound states for a wide range of parameters. We further investigate the behavior of the topological gap and its dependence on the type of d-wave pairing, i.e., d, d+is, or d+id', and note the difficulties that can arise due to the presence of gapless excitations in pure d-wave superconductors. On the other hand, the planar Josephson junctions based on superconductors with d+is and d+id' pairings can potentially lead to realizations of Majorana bound states. Our proposal can be realized in cuprate superconductors, e.g., in a twisted bilayer, combined with the layered semiconductor Bi2O2Se.

cond-mat.supr-con↗