arXiv subjects

Jian-Ping Wang

Publications and source records attributed to Jian-Ping Wang.

At least 19 recordsLinked to original sources

arXiv2026

Epitaxial Strain Activates Altermagnetic Spin-Splitting Torques in RuO2(100)

The altermagnetic nature of rutile RuO2 remains under active debate: bulk measurements indicate a nearly nonmagnetic ground state, whereas thin-film studies have reported symmetry-dependent transport signatures consistent with altermagnetism. Here, we provide experimental evidence that altermagnetic spin splitting in RuO2 is a strain-stabilized emergent state rather than an intrinsic bulk property. Angular-resolved spin-torque measurements reveal a symmetry-selected spin Hall response characteristic of altermagnetic spin splitting, which is strongest in the strained regime but progressively suppressed as the lattice relaxes toward the bulk limit. Complementary magnetic measurements further reveal enhanced coercivity and exchange-bias behavior exclusively in strained films, indicating the emergence of a strain-stabilized magnetic state. First-principles calculations reproduce the strain-dependent evolution of the Neel order and spin-split electronic structure, supporting the experimental observations. Together, these results establish altermagnetic spin splitting in RuO2 as a strain-stabilized emergent state and provide a unified explanation for the long-standing discrepancy between bulk and thin-film observations.

cond-mat.mtrl-sci↗

arXiv2026

Van Hove Singularity and Phase Instability: Exploring the Role of Electron Correlation in the Magnetic Behavior of $\mathrm{Fe}_{16}\mathrm{N}_2$

The ordered iron nitride phase $α''-\mathrm{Fe}_{16}\mathrm{N}_2$ is a promising candidate for environment-friendly, rare-earth-free permanent magnets due to its demonstrated giant saturation magnetization ($M_s$). However, first-principles electronic-structure calculations have struggled to consistently reproduce experimentally-observed high $M_s$, and have yielded highly variable magneto-crystalline anisotropy (MCA) values. In this work, we employ Density Functional Theory under the GGA+$U$ framework to study the effect of the Hubbard parameters $U$ and $J$ on the magnetic properties of $\mathrm{Fe}_{16}\mathrm{N}_2$. We demonstrate that the electronic structure exhibits high sensitivity to these parameters, specifically uncovering a van Hove singularity near the Fermi level ($E_F$), inherently tied to the material's structural and thermal phase instability. By linking this topological anomaly to the calculated magnetic properties, we demonstrate that the selection of $U$ not only tunes $M_s$ and MCA energy towards experimental values but also reveals an underlying electronic mechanism potentially responsible for the phase's metastability. This provides a framework for understanding the correlation-driven magnetic behavior of $\mathrm{Fe}_{16}\mathrm{N}_2$ and offers a pathway for optimizing its stability and performance in practical applications.

cond-mat.str-el↗

arXiv2026

Strain-Driven Altermagnetic Spin Splitting Effect in RuO$_2$

The non-relativistic spin-momentum locking in altermagnets gives rise to a time-reversal-odd spin Hall effect, known as the altermagnetic spin-splitting effect (ASSE). Although ASSE was first reported in RuO$_2$, subsequent experiments have yielded inconsistent results, leaving its spin-transport mechanism unclear. Here, we systematically investigate how strain, crystal orientation, and the Hubbard $U$ parameter influence the magnetic ground state and spin Hall response of RuO$_2$. Guided by recent experimental observations, we find that $U$ is likely smaller than the value required to induce intrinsic magnetism, suggesting that bulk RuO$_2$ and (001)/(101) RuO$_2$ thin films grown on TiO$_2$ are nonmagnetic in the absence of extrinsic effects. In contrast, (100) and (110) films exhibit strain-induced altermagnetic spin splitting, leading to a strong ASSE even without Hubbard $U$ corrections. These results reconcile previous experimental discrepancies and provide design guidelines for RuO$_2$-based spintronic devices.

cond-mat.mtrl-sci↗

arXiv2026

CRAM-ER: Error-Resilient Spintronic Computational Random Access Memory for Scalable In-Memory Computation

Deep neural networks (DNNs) have achieved state-of-the-art performance across diverse domains. However, typical Von Neumann compute paradigms face severe memory bottlenecks. Emerging near-memory and compute-in-memory approaches alleviate this but incur significant peripheral overhead. Computational Random Access Memory (CRAM) based on MRAM enables in-situ logic without peripheral overhead, offering a dense, energy-efficient solution. However, probabilistic MRAM switching induces gate-level errors that limit the scalability and reliability of CRAM for accelerating DNN. Moreover, the large number of sequential MRAM writes severely constrains CRAM throughput. To address these challenges, we propose an error-resilient CRAM (CRAM-ER) architecture for scalable in-memory matrix-vector multiplications (MVMs). Our error-aware hardware-software co-design framework leverages a hybrid spintronic-CRAM + CMOS adder-tree architecture to mitigate the impact of device-level errors, demonstrating MVM functionality with high area and energy efficiency. We further develop an error-aware model fine-tuning and fine-grained error correction for enhanced error resilience. Evaluations of the CMOS+spintronic hybrid architecture on DNN benchmarks show near-lossless accuracy while reducing CRAM latency by up to 2 orders of magnitude, outperforming CPU/GPU+high-bandwidth DRAM in both energy efficiency and energy-delay product.

cs.AR↗

arXiv2026

High-Frequency Switching in Superparamagnetic Magnetic Tunnel Junctions by Enhancing Damping

Superparamagnetic magnetic tunnel junctions (sMTJs) are promising components for true random number generation and probabilistic computing. Achieving high-frequency fluctuation while maintaining reliable control over output level is critical for applications. In this work, we systematically investigate the role of magnetic damping in regulating thermal switching rates using macrospin simulations. We show that enhanced damping accelerates the switching rate by increasing the escape rate over the energy barrier. We further compare two control mechanisms: spin-transfer torque (STT) and voltage-controlled exchange coupling (VCEC). Our results reveal that STT-based switching is strongly suppressed under high damping, whereas VCEC, by reshaping the energy landscape without relying on torque-driven dynamics, retains high control efficiency. These findings suggest that enhanced damping not only enables faster stochastic switching in sMTJs but also makes VCEC inherently better suited than STT for high-frequency applications.

physics.app-ph↗

arXiv2025

Interface-engineered voltage-driven magnetic tunnel junctions with ultra-low-energy magnetization switching

Electric-field control of spin states offers a promising route to ultra-low-power, ultra-fast magnetization switching in spintronic devices such as magnetic tunnel junctions (MTJs). Recent progress in modulating spin-orbit interactions at the interfaces between 3d transition-metal ferromagnets and dielectric layers has underscored the role of atomic-scale heavy-metal doping in optimizing device performance. Here, we experimentally demonstrate highly energy-efficient, voltage-driven magnetization switching in MTJs exhibiting large tunnel magnetoresistance (TMR), enabled by a remote doping technique that precisely controls the iridium (Ir) concentration near the MgO-CoFeB interface in the free layer. Our devices achieve a switching energy of only 3.5 fJ per bit for nanoscale MTJs operating in the sub-nanosecond regime, while maintaining a TMR ratio up to 160 percent after 400 C post-annealing. These findings establish a viable pathway toward scalable, ultra-low-power nonvolatile memory, positioning voltage-driven MTJs as strong contenders for next-generation magnetoresistive random-access memory (MRAM) and other emerging spintronic applications.

cond-mat.mes-hall↗

arXiv2025

Demonstration of Electron-Mediated Voltage-Controlled Exchange Coupling in Perpendicular Magnetic Tunnel Junctions

Electron-mediated voltage control of exchange coupling (EM-VCEC) has been proposed as a mechanism for magnetization switching via modulation of spin-dependent electron reflection. However, its experimental verification has been challenging due to the coexistence of slower, voltage-induced ionic effects. Here, we fabricate magnetic tunnel junction (MTJ) devices that enable nanosecond timescale voltage application. Our results reveal rapid exchange coupling modulation on the nanosecond timescale, consistent with an electronic origin. The observed enhancement and saturation at low temperatures further rule out ionic migration, conclusively confirming the electronic nature of the mechanism. These results establish EM-VCEC as a viable mechanism for fast and energy-efficient voltage-driven magnetic switching.

physics.app-ph↗

arXiv2025

Modulation of switching dynamics in magnetic tunnel junctions for low-error-rate computational random-access memory

The conventional computer architecture has been facing challenges answering the ever-increasing demands from emerging applications, such as AI, for energy-efficient computation and memory hardware systems. Computational Random Access Memory (CRAM) represents a true in-memory computing paradigm that integrates logic and memory functions within the same array. At its core, CRAM relies on Magnetic Tunnel Junctions (MTJs), which serve as the foundational building blocks for implementing both memory storage and logic operations. However, a key challenge in CRAM lies in the non-ideal error rates associated with switching dynamics of MTJs, necessitating innovative approaches to reduce errors and optimize logic margins. This work proposes a novel approach of utilizing the voltage-controlled magnetic anisotropy (VCMA) to steepen the switching probability transfer curve (SPTC), thereby significantly reducing the logic operation error rate in CRAM. Using several numerical modeling tools, we validate the effectiveness of VCMA in modulating the energy barrier and switching dynamics in MTJs. It is revealed that the VCMA effect significantly reduces the error rate of CRAM by 61.43% at a VCMA coefficient of 200 fJ/V/m compared to CRAM without VCMA. The reduction of error rate is further rapidly amplified with an increasing TMR ratio. Furthermore, the introduction of the VCMA effect decreases the logic voltage (Vlogic) required for logic operations in CRAM and results in reduction of energy consumption. Our work serves as a first exploration in reducing the error rate in CRAM by modifying SPTC in MTJs.

cs.ET↗

arXiv2025

Optimizing Time-resolved Magneto-optical Kerr Effect for High-fidelity Magnetic Characterization

Spintronics has emerged as a key technology for fast and non-volatile memory with great CMOS compatibility. As the building blocks for these cutting-edge devices, magnetic materials require precise characterization of their critical properties, such as the effective anisotropy field ($H_{\rm{k,eff}}$, related to magnetic stability) and damping ($α$ key factor in device energy efficiency). Accurate measurements of these properties are essential for designing and fabricating high-performance spintronic devices. Among advanced metrology techniques, Time-resolved Magneto-Optical Kerr Effect (TR-MOKE) stands out for its superb temporal and spatial resolutions, surpassing traditional methods like ferromagnetic resonance (FMR). However, the full potential of TR-MOKE has not yet been fully pledged due to the lack of systematic optimization and robust operational guidelines. In this study, we address this gap by developing experimentally validated guidelines for optimizing TR-MOKE metrology across materials with perpendicular magnetic anisotropy (PMA) and in-plane magnetic anisotropy (IMA). Our work identifies the optimal ranges of the field angle to simultaneously achieve high signal amplitudes and improve measurement sensitivities to $H_{\rm{k,eff}}$ and $α$. By suppressing the influence of inhomogeneities and boosting sensitivity, our work significantly enhances TR-MOKE capability to extract magnetic properties with high accuracy and reliability. This optimization framework positions TR-MOKE as an indispensable tool for advancing spintronics, paving the way for energy-efficient and high-speed devices that will redefine the landscape of modern computing and memory technologies.

cond-mat.mes-hall↗

arXiv2025

Anomalous vortex Hall effect in a ferromagnet/superconductor heterostructure

The coexistence of superconductivity and ferromagnetism is a fascinating and complex phenomenon in condensed matter physics, as these two states are typically mutually exclusive due to their competing spin configurations. However, the interplay between these two orders through the proximity effect has been a subject of intense research as it opens up possibilities for novel technological applications. Here, we report the coexistence of superconductivity and ferromagnetism in superconducting δ-TaN/ferromagnetic CoFeB heterostructures grown by facing-target sputtering. Superconducting states are comprehensively investigated, with evidence of strong correlation between the superconducting and ferromagnetic order parameters. In particular, we observed an anomalous Hall signal without the presence of the magnetic field in the mixed state of the superconducting transition near the critical temperature. Systematic characterizations of the Hall resistance under varying temperatures and magnetic fields attribute this behavior to the vortex Hall effect (VHE), whereby superconducting vortices in the mixed state undergo transverse motions near the critical temperature. Unlike previously reported VHEs in conventional type-II superconductors, the anomalous VHE in TaN is induced by the stray field in the underlying CoFeB layers. The concurrency of strong spin-orbit coupling, the superconductivity in the TaN layer, and the highly spin-polarized ferromagnetic ordering in the CoFeB layer offers new insights into proximity-induced vortex dynamics and the design of novel superconducting spintronic devices.

cond-mat.supr-con↗

arXiv2025

Coexistence of unconventional spin Hall effect and antisymmetric planar Hall effect in IrO$_2$

Crystal symmetry plays an important role in the Hall effects. Unconventional spin Hall effect (USHE), characterized by Dresselhaus and out-of-plane spins, has been observed in materials with low crystal symmetry. Recently, antisymmetric planar Hall effect (APHE) was discovered in rutile RuO2 and IrO2 (101) thin films, which also exhibit low crystal symmetry. In this study, we report the observation of both USHE and APHE in IrO2 (111) films, using spin-torque ferromagnetic resonance (ST-FMR) and harmonic Hall measurements, respectively. Notably, the unconventional spin torque efficiency from Dresselhaus spin was more than double that of a previous report. Additionally, the temperature dependence of APHE suggests that it arises from the Lorentz force, constrained by crystal symmetry. Symmetry analysis supports the coexistence of USHE and APHE and demonstrates that both originate from the crystal symmetry of IrO2 (111), paving the way for a deeper understanding of Hall effects and related physical phenomena.

cond-mat.mes-hall↗

arXiv2025

Fast spin precession and strong perpendicular magnetic anisotropy in ferrimagnetic Mn4N thin films improved by Pd buffer layer

Ferrimagnets take the advantages of both ferromagnets and antiferromagnets making them promise for spintronic applications. Here we prepared ferrimagnetic Mn4N thin films with high Curie temperature and investigated the crystalline structure and magnetic properties affected by the Pd buffer layer. We demonstrated that both crystalline quality and perpendicular magnetic anisotropy (PMA) of Mn4N thin films are enhanced significantly due to the relaxation of tensile stress induced by the Pd buffer layer. We also demonstrated a fast spin precession at room temperature, almost 100 GHz, in Mn4N thin films. With the characteristics of high thermal stability, enhanced PMA by buffer layer and fast spin precession, Mn4N thin film is a promising material for spintronic applications.

cond-mat.mtrl-sci↗

arXiv2025

Enhancing Unconventional Spin-Orbit Torque Efficiency: Numerical Study on the Influence of Crystallographic Texture and Polycrystalline Effects on Low-Symmetry Materials

Spin-orbit torque (SOT) has been extensively studied as a key mechanism in spintronics applications. However, conventional SOT materials limit the spin polarization direction to the in-plane orientation, which is suboptimal for efficient magnetization switching. Recently, spin currents with spin polarization along multiple directions have been observed in low-symmetry materials, offering a promising energy-efficient strategy for the field-free switching of magnetic materials with perpendicular magnetic anisotropy. However, the efficiency of this mechanism is highly dependent on the crystallographic texture of the SOT materials, a critical factor that, to date, has not been quantitatively investigated. In this study, we present a comprehensive numerical investigation into the impact of both in-plane and out-of-plane crystallographic textures of SOT materials on the unconventional SOT generated by Dresselhaus-like and out-of-plane spin polarizations. By employing a theoretical orientation distribution function, we calculate the effective unconventional SOT values for SOT materials with tunable crystallographic texture. This analysis provides a framework for the synthesis and optimization of future low-symmetry SOT materials, which can enhance operational efficiency for spintronics applications in magnetoresistive random-access memory and spin logic devices.

cond-mat.mes-hall↗

arXiv2024

Energy Efficient Stochastic Signal Manipulation in Superparamagnetic Tunnel Junctions via Voltage-Controlled Exchange Coupling

Superparamagnetic tunnel junctions (sMTJs) are emerging as promising components for stochastic units in neuromorphic computing, owing to their tunable random switching behavior. Conventional MTJ control methods, such as spin-transfer torque (STT) and spin-orbit torque (SOT), often require substantial power. Here, we introduce the voltage-controlled exchange coupling (VCEC) mechanism, enabling switching between antiparallel and parallel states in sMTJs with an ultralow power consumption of only 40 nW, approximately two orders of magnitude lower than conventional STT-based sMTJs. This mechanism yields a sigmoid-shaped output response, making it ideally suited for neuromorphic computing applications. Furthermore, we validate the feasibility of integrating VCEC with the SOT current control, offering an additional dimension for magnetic state manipulation. This work marks the first practical demonstration of VCEC effect in sMTJs, highlighting its potential as a low-power control solution for probabilistic bits in advanced computing systems.

physics.app-ph↗

arXiv2024

Giant spin Hall effect with multi-directional spin components in Ni4W

Spin-orbit torque (SOT) can be used to efficiently manipulate the magnetic state of magnetic materials, which is an essential element for memory and logic applications. Due to symmetry constraints, only in-plane spins can be injected into the ferromagnet from the underlying SOT layer for conventional SOT materials such as heavy metals and topological materials. Through the use of materials with low symmetries, or other symmetry breaking approaches, unconventional spin currents with out-of-plane polarization has been demonstrated and enabled field-free deterministic switching of perpendicular magnetization. Despite this progress, the SOT efficiency of these materials has typically remained low. Here, we report a giant SOT efficiency of 0.85 in sputtered Ni4W/CoFeB heterostructure at room temperature, as evaluated by second harmonic Hall measurements. In addition, due to the low crystal symmetry of Ni4W, unconventional out-of-plane and Dresselhaus-like spin components were observed. Macro-spin simulation suggests our spin Hall tensor to provide about an order of magnitude improvement in the magnetization switching efficiency, thus broadening the path towards energy efficient spintronic devices using low-symmetry materials.

cond-mat.mes-hall↗

arXiv2024

Experimental demonstration of magnetic tunnel junction-based computational random-access memory

Conventional computing paradigm struggles to fulfill the rapidly growing demands from emerging applications, especially those for machine intelligence, because much of the power and energy is consumed by constant data transfers between logic and memory modules. A new paradigm, called "computational random-access memory (CRAM)" has emerged to address this fundamental limitation. CRAM performs logic operations directly using the memory cells themselves, without having the data ever leave the memory. The energy and performance benefits of CRAM for both conventional and emerging applications have been well established by prior numerical studies. However, there lacks an experimental demonstration and study of CRAM to evaluate its computation accuracy, which is a realistic and application-critical metrics for its technological feasibility and competitiveness. In this work, a CRAM array based on magnetic tunnel junctions (MTJs) is experimentally demonstrated. First, basic memory operations as well as 2-, 3-, and 5-input logic operations are studied. Then, a 1-bit full adder with two different designs is demonstrated. Based on the experimental results, a suite of modeling has been developed to characterize the accuracy of CRAM computation. Scalar addition, multiplication, and matrix multiplication, which are essential building blocks for many conventional and machine intelligence applications, are evaluated and show promising accuracy performance. With the confirmation of MTJ-based CRAM's accuracy, there is a strong case that this technology will have a significant impact on power- and energy-demanding applications of machine intelligence.

cs.ET↗

arXiv2024

On Error Correction for Nonvolatile Processing-In-Memory

Processing in memory (PiM) represents a promising computing paradigm to enhance performance of numerous data-intensive applications. Variants performing computing directly in emerging nonvolatile memories can deliver very high energy efficiency. PiM architectures directly inherit the vulnerabilities of the underlying memory substrates, but they also are subject to errors due to the computation in place. Numerous well-established error correcting codes (ECC) for memory exist, and are also considered in the PiM context, however, they typically ignore errors that occur throughout computation. In this paper we revisit the error correction design space for nonvolatile PiM, considering both storage/memory and computation-induced errors, surveying several self-checking and homomorphic approaches. We propose several solutions and analyze their complex performance-area-coverage trade-off, using three representative nonvolatile PiM technologies. All of these solutions guarantee single error correction for both, bulk bitwise computations and ordinary memory/storage errors.

cs.ET↗

arXiv2023

Room Temperature Spin to Charge Conversion in Amorphous Topological Insulating Gd-Alloyed BixSe1-x/CoFeB Bilayers

Disordered topological insulator (TI) films have gained intense interest by benefiting from both the TIs exotic transport properties and the advantage of mass production by sputtering. Here, we report on the clear evidence of spin-charge conversion (SCC) in amorphous Gd-alloyed BixSe1-x (BSG)/CoFeB bilayers fabricated by sputtering, which could be related to the amorphous TI surface states. Two methods have been employed to study SCC in BSG/CoFeB(5 nm) bilayers with different BSG thicknesses. Firstly, spin pumping is used to generate a spin current in CoFeB and to detect SCC by inverse Edelstein effect. The maximum SCC efficiency (SCE) is measured as large as 0.035 nm in a 6 nm thick BSG sample, which shows a strong decay when tBSG increases due to the increase of BSG surface roughness. The second method is the THz time-domain spectroscopy, which reveals a small tBSG dependence of SCE, validating the occurrence of a pure interface state related SCC. Furthermore, our angle-resolved photoemission spectroscopy data show dispersive two-dimensional surface states that cross the bulk gap until to the Fermi level, strengthening the possibility of SCC due to the amorphous TI states. Our studies provide a new experimental direction towards the search for topological systems in the amorphous solids.

cond-mat.mtrl-sci↗