arXiv subjects

Pranaba Kishor Muduli

Publications and source records attributed to Pranaba Kishor Muduli.

9 recordsLinked to original sources

arXiv2026

Topologically Driven Giant Effective Spin Mixing Conductance in Antiferromagnetic FeSn/Py Heterostructures

The topological semimetal FeSn antiferromagnet, characterized by its kagome lattice, two-dimensional flat bands, and Dirac-like surface states, holds immense promise for spintronic applications. In this work, for the first time, we investigate the spin pumping behavior in epitaxial-FeSn/Py (Ni$_{80}$Fe$_{20}$) heterostructures. We report a giant effective spin mixing conductance (g$^{\uparrow \downarrow}_{\mathrm{eff}}$) of $(116\pm 7)$~nm$^{-2}$, which is nearly one order of magnitude higher than that of standard Pt/Py heterostructures. The insertion of a 3 nm Al spacer layer results in a two-fold reduction in the effective damping, confirming the interfacial origin of the large g$^{\uparrow\downarrow}_{\mathrm{eff}}$. Consistently, we observe an order-of-magnitude higher inverse spin Hall effect voltage in the FeSn/Py system compared to a reference Pt/Py film stack. We attribute the giant g$^{\uparrow\downarrow}_{\mathrm{eff}}$ to the direct interfacing of the Py layer with the topologically active [001]-kagome surface of epitaxial-FeSn. These findings establish the critical role of topologically active interfaces for advanced quantum-material-based spintronic devices.

cond-mat.mes-hall↗

arXiv2026

Giant Damping-like Spin-Torque Conductivity in a GeTe/Py van der Waals Heterostructure

Recent observations of large unconventional spin-orbit torques in van der Waals (vdW) materials are driving intense interest for energy-efficient spintronic applications. A key limitation of ferromagnet (FM)/vdW heterostructures is their lower value of damping-like torque conductivity ($σ{\rm_{DL}^{y}}$) compared to the conventional heavy metal-based systems, limiting their prospects for commercial spintronic devices. Here, we report both a giant $σ{\rm_{DL}^{y}}$ of $-(1.25 \pm 0.11)\times 10^{5}~\hbar/ 2e~Ω^{-1}$m$^{-1}$ and an unconventional spin-orbit torque in a heterostructure comprising an FM (Ni$_{80}$Fe$_{20}$) and the vdW material GeTe. The value of $σ{\rm_{DL}^{y}}$ represents the highest reported torque conductivity for any FM/vdW interface and is comparable to benchmark heavy metal heterostructures. First-principles calculations reveal that this substantial torque originates from the cooperative interplay of the spin Hall effect, orbital Hall effect, and orbital Rashba effect, assisted by interfacial charge transfer. These findings demonstrate the potential of carefully engineered vdW heterostructures to achieve highly efficient electrical manipulation of magnetization at room temperature, paving the way for next-generation low-power spintronic devices.

cond-mat.mes-hall↗

arXiv2025

Symmetry Enhanced Unconventional Spin Current Anisotropy in a Collinear Antiferromagnet

Spin-orbit torque (SOT) presents a promising avenue for energy-efficient spintronics devices, surpassing the limitations of spin transfer torque. While extensively studied in heavy metals, SOT in antiferromagnetic quantum materials remains largely unexplored. Here, we investigate SOT in epitaxial FeSn, a collinear antiferromagnet with a kagome lattice. FeSn exhibits intriguing topological quantum features, including two-dimensional flat bands and Dirac-like surface states, making it an ideal platform for investigating emergent SOT properties. Using spin-torque ferromagnetic resonance, we uncover a six-fold symmetric damping-like SOT in epitaxial-FeSn/Py heterostructures, reflecting the six-fold symmetry of the epitaxial [0001]-oriented FeSn films. Additionally, we observe a substantial unconventional field-like torque, originating from spin currents with out-of-plane spin polarization. This torque exhibits a unique angular dependence-a superposition of six-fold crystalline symmetry and uniaxial symmetry associated with the antiferromagnetic spin Hall effect. Notably, the unconventional field-like torque is enhanced when the RF current flows along the Neel vector in FeSn. Our findings reveal an unconventional spin current anisotropy tunable by crystalline and magnetic symmetry, offering a novel approach for controlling SOT in antiferromagnetic spintronics.

cond-mat.mes-hall↗

arXiv2024

Ultra-fast spin Hall nano-oscillator based microwave spectral analysis

Ultra-fast spectrum analysis concept based on rapidly tuned spintronic nano-oscillators has been under development for the last few years and has already demonstrated promising results. Here, we demonstrate an ultra-fast microwave spectrum analyzer based on a chain of five mutually synchronized nano-constriction spin Hall nano-oscillators (SHNOs). As mutual synchronization affords the chain a much improved signal quality, with linewidths well below 1 MHz at close to a 10 GHz operating frequency, we observe an order of magnitude better frequency resolution bandwidth compared to previously reported spectral analysis based on single magnetic tunnel junction based spin torque nano-oscillators. The high-frequency operation and ability to synchronize long SHNO chains and large arrays make SHNOs ideal candidates for ultra-fast microwave spectral analysis.

cond-mat.mes-hall↗

arXiv2023

Interfacial origin of unconventional spin-orbit torque in Py/$γ-$IrMn$_{3}$

Angle-resolved spin-torque ferromagnetic resonance measurements are carried out in heterostructures consisting of Py (Ni$_{81}$Fe$_{19}$) and a noncollinear antiferromagnetic quantum material $γ-$IrMn$_{3}$. The structural characterization reveals that $γ-$IrMn$_{3}$ is polycrystalline in nature. A large exchange bias of 158~Oe is found in Py/$γ-$IrMn$_{3}$ at room temperature, while $γ-$IrMn$_{3}$/Py and Py/Cu/$γ-$IrMn$_{3}$ exhibited no exchange bias. Regardless of the exchange bias and stacking sequence, we observe a substantial unconventional out-of-plane anti-damping torque when $γ-$IrMn$_{3}$ is in direct contact with Py. The magnitude of the out-of-plane spin-orbit torque efficiency is found to be twice as large as the in-plane spin-orbit torque efficiency. The unconventional spin-orbit torque vanishes when a Cu spacer is introduced between Py and $γ-$IrMn$_{3}$, indicating that the unconventional spin-orbit torque in this system originates at the interface. These findings are important for realizing efficient antiferromagnet-based spintronic devices via interfacial engineering.

cond-mat.mtrl-sci↗

arXiv2022

Large spin Hall conductivity in epitaxial thin films of kagome antiferromagnet Mn$_3$Sn at room temperature

Mn$_3$Sn is a non-collinear antiferromagnetic quantum material that exhibits a magnetic Weyl semimetallic state and has great potential for efficient memory devices. High-quality epitaxial $c$-plane Mn$_3$Sn thin films have been grown on a sapphire substrate using a Ru seed layer. Using spin pumping induced inverse spin Hall effect measurements on $c$-plane epitaxial Mn$_3$Sn/Ni$_{80}$Fe$_{20}$, we measure spin-diffusion length ($λ_{\rm Mn_3Sn}$), and spin Hall conductivity ($σ_{\rm{SH}}$) of Mn$_3$Sn thin films: $λ_{\rm Mn_3Sn}=0.42\pm 0.04$ nm and $σ_{\rm{SH}}=-702~\hbar/ e~Ω^{-1}$cm$^{-1}$. While $λ_{\rm Mn_3Sn}$ is consistent with earlier studies, $σ_{\rm{SH}}$ is an order of magnitude higher and of the opposite sign. The behavior is explained on the basis of excess Mn, which shifts the Fermi level in our films, leading to the observed behavior. Our findings demonstrate a technique for engineering $σ_{\rm{SH}}$ of Mn$_3$Sn films by employing Mn composition for functional spintronic devices.

cond-mat.mtrl-sci↗

arXiv2020

Skyrmion-antiskyrmion droplets in a chiral ferromagnet

We find numerically skyrmionic textures with skyrmion number Q=0 in ferromagnets with the Dzyaloshinskii-Moriya interaction and perpendicular anisotropy. These have the form of a skyrmion-antiskyrmion pair and may be called chiral droplets. They are stable in an infinite film as well as in disc-shaped magnetic elements. Droplets are found for values of the parameters close to the transition from the ferromagnetic to the spiral phase. We study their motion under spin-transfer torque. They move in the direction of the spin flow and, thus, their dynamics are drastically different than the Hall dynamics of the standard Q=0 skyrmion.

cond-mat.mes-hall↗

arXiv2019

Direct Observation of Unusual Interfacial Dzyaloshinskii-Moriya Interaction in Graphene/NiFe/Ta Heterostructure

Graphene/ferromagnet interface promises a plethora of new science and technology. The interfacial Dzyaloshinskii Moriya interaction (iDMI) is essential for stabilizing chiral spin textures, which are important for future spintronic devices. Here, we report direct observation of iDMI in graphene/Ni80Fe20/Ta heterostructure from non-reciprocity in spin-wave dispersion using Brillouin light scattering (BLS) technique. Linear scaling of iDMI with the inverse of Ni80Fe20 thicknesses suggests primarily interfacial origin of iDMI. Both iDMI and spin-mixing conductance increase with the increase in defect density of graphene obtained by varying argon pressure during sputter deposition of Ni80Fe20. This suggests that the observed iDMI originates from defect-induced extrinsic spin-orbit coupling at the interface. The direct observation of iDMI at graphene/ferromagnet interface without perpendicular magnetic anisotropy opens new route in designing thin film heterostructures based on 2-D materials for controlling chiral spin structure such as skyrmions and bubbles, and magnetic domain-wall-based storage and memory devices.

cond-mat.mtrl-sci↗

arXiv2018

Chiral skyrmion auto-oscillations in a ferromagnet under spin transfer torque

A skyrmion can be stabilized in a nanodisc geometry in a ferromagnetic material with Dzyaloshinskii-Moriya (DM) interaction. We apply spin torque uniform in space and time and observe numerically that the skyrmion is set in steady rotational motion around a point off the nanodisc center. We give a theoretical description of the emerging auto-oscillation dynamics based on the coupling of the rotational motion to the breathing mode of the skyrmion and to the associated oscillations of the in-plane magnetization. The analysis shows that the achievement of auto-oscillations in this simple set-up is due to the chiral symmetry breaking. Thus, we argue that the system is turned into a spin-torque oscillator due to the chiral DM interaction.

cond-mat.mes-hall↗