arXiv subjects

Subhankar Bedanta

Publications and source records attributed to Subhankar Bedanta.

At least 19 recordsLinked to original sources

arXiv2026

Interface-resolved structural properties of epitaxial Y$_3$Fe$_5$O$_{12}$/ Gd$_3$Fe$_5$O$_{12}$ bilayers grown on GGG(111) by pulsed laser deposition

Epitaxial Y$_3$Fe$_5$O$_{12}$ (YIG) and Gd$_3$Fe$_5$O$_{12}$ (GdIG) thin films, along with their bilayer heterostructures, were grown on Gd$_3$Ga$_5$O$_{12}$(GGG)(111) substrates using pulsed laser deposition. Structural properties were investigated using X-ray diffraction, reciprocal space mapping, and cross-sectional transmission electron microscopy. The results confirm high crystalline quality and coherent epitaxial growth, with RSM revealing a coexistence of strained and partially relaxed regions governed by layer sequence. TEM analysis shows sharp interfaces, columnar microstructures, and antiphase boundaries that facilitate strain relaxation. A comparative study indicates that the GGG/YIG/GdIG stacking sequence exhibits improved structural quality with reduced defect density, attributed to the superior epitaxial growth of YIG on the substrate. These findings highlight the critical role of growth sequence in controlling strain and interfacial structure in garnet heterostructures.

cond-mat.mtrl-sci↗

arXiv2025

Thermal Evolution of Skyrmions in Synthetic Ferrimagnets of Co/Gd Heterostructure for Topological Spintronic Applications

Synthetic ferrimagnetic (SFiM) multilayers offer a versatile platform for hosting skyrmions with tunable magnetic properties, combining the advantages of ferromagnets and antiferromagnets. Unlike synthetic antiferromagnets, SFiMs retain a finite magnetization that allows direct observation of magnetic textures while still benefiting from reduced dipolar fields and a suppressed skyrmion Hall effect. However, a systematic investigation of their temperature and field dependent magnetization evolution, including the labyrinthine-to-skyrmion transition in Co/Gd-based SFiMs, remains less explored. Here, we demonstrate the stabilization of 70 nm-radius skyrmions at room temperature and reveal how the Co and Gd sublattices influence the temperature-dependent net magnetization. Further, we develop a microscopic spin model for SFiM incorporating the relevant magnetic interactions, which reproduces the experimental observations and captures the temperature-dependent magnetic phase evolution. This framework highlights the interplay of fundamental interactions controlling skyrmion stability in SFiM and provides a pathway for engineering heterostructures for topological spintronic applications.

cond-mat.mtrl-sci↗

arXiv2025

Robust Superconductivity and High Upper Critical Fields in Epitaxial cubic W2N Thin Films

Transition Metal Nitrides are a versatile class of materials, combining chemical robustness, high hardness, and superconducting behaviour with critical temperatures between 2 to 10 K. While several binary TMNs have been explored, superconductivity in stoichiometric W2N has remained largely unexplored. Here, we report on superconducting thin films of stoichiometric W2N, demonstrating a distinctly high upper critical field of 8.5 T, uncommon among binary TMNs. This robust superconducting response under high magnetic fields highlights the technological relevance of W2N for integrated quantum and cryogenic electronic platforms. Overall, these results position stoichiometric W2N as a promising addition to the TMN superconducting landscape, opening new avenues for functional materials design based on chemically stable and mechanically resilient nitrides.

cond-mat.supr-con↗

arXiv2025

Effect of RKKY and dipolar interaction on the nucleation of skyrmion in Pt/Co multilayer with Ir spacer

Magnetic skyrmions, topologically protected spin textures, have emerged as promising candidates for next-generation spintronic applications. In this study, we investigate the stabilization of skyrmionic states in a uniquely engineered Pt/Co multilayer system with an Ir spacer, where both Ruderman Kittel Kasuya Yosida (RKKY) and dipolar interactions play a crucial role. The studied multilayer structure consists of a synthetic antiferromagnetic (SAF) configuration, where a single Ir layer facilitates strong antiferromagnetic coupling between two ferromagnetic regions: FM1 (top) and FM2 (bottom), each formed by repeated Co layers separated by Pt, enabling significant dipolar interactions. This FM1/Ir/FM2 configuration results in a distinctive skyrmionic hysteresis loop, driven by the interplay of dipolar and RKKY interactions. Magnetic force microscopy (MFM) imaging confirms the nucleation of isolated skyrmions, while magnetotransport measurements reveal a finite topological Hall effect (THE), indicating the chiral nature of these spin textures. Furthermore, we demonstrate that increasing the Co layer thickness leads to a reduction in magnetic anisotropy, which in turn results in the formation of relatively larger and denser skyrmions. Our findings establish a robust approach for stabilizing skyrmions through the combined effects of dipolar and RKKY interactions, offering new pathways for controlled skyrmion manipulation in spintronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Lattice Mismatch Driven In Plane Strain Engineering for Enhanced Upper Critical Fields in Mo2N Superconducting Thin Films

Transition metal nitrides are a fascinating class of hard coating material that provide an excellent platform for investigating superconductivity and fundamental electron phonon interactions. In this work the structural morphological and superconducting properties have been studied for Mo2N thin films deposited via direct current magnetron sputtering on cplane Al2O3 and MgO substrates to elucidate the effect of internal strain on superconducting properties. High resolution X Ray diffraction and time of flight elastic recoil detection analysis confirms the growth of single phase Mo2N thin films exhibiting epitaxial growth with twin domain structure. Low temperature electrical transport measurements reveal superconducting transitions at 5.2 K and 5.6 K with corresponding upper critical fields of 5 T and 7 T for the films deposited on Al2O3 and MgO, respectively. These results indicate strong type II superconductivity and the observed differences in superconducting properties are attributed to substrate induced strain which leads to higher e ph coupling for the film on MgO substrate. These findings highlight the tunability of superconducting properties in Mo2N films through strategic substrate selection.

cond-mat.supr-con↗

arXiv2024

Enhancement of spin Hall angle by an order of magnitude via Cu intercalation in MoS$_2$/CoFeB heterostructures

Transition metal dichalcogenides (TMDs) are a novel class of quantum materials with significant potential in spintronics, optoelectronics, valleytronics, and opto-valleytronics. TMDs exhibit strong spin-orbit coupling, enabling efficient spin-charge interconversion, which makes them ideal candidates for spin-orbit torque-driven spintronic devices. In this study, we investigated the spin-to-charge conversion through ferromagnetic resonance in MoS$_2$/Cu/CoFeB heterostructures with varying Cu spacer thicknesses. The conversion efficiency, quantified by the spin Hall angle, was enhanced by an order of magnitude due to Cu intercalation. Magneto-optic Kerr effect microscopy confirmed that Cu did not significantly modify the magnetic domains, indicating its effectiveness in decoupling MoS$_2$ from CoFeB. This decoupling preserves the spin-orbit coupling (SOC) of MoS$_2$ by mitigating the exchange interaction with CoFeB, as proximity to localized magnetization can alter the electronic structure and SOC. First-principles calculations revealed that Cu intercalation notably enhances the spin Berry curvature and spin Hall conductivity, contributing to the increased spin Hall angle. This study demonstrates that interface engineering of ferromagnet/TMD-based heterostructures can achieve higher spin-to-charge conversion efficiencies, paving the way for advancements in spintronic applications.

cond-mat.mtrl-sci↗

arXiv2024

Capping layer dependent anti-correlation between magnetic damping and spin-orbital to charge conversion

The magnetic Gilbert damping and spin-orbital to charge interconversion phenomenon play vital role in controlling the modern spintronics device performances. Though the ferromagnets (FMs) and heavy metals (HMs) are considered to be the key components of the future spin-orbit torque magnetic random access memory (SOT-MRAM) devices, recently the integration of lighter materials with low intrinsic spin-orbit coupling (SOC) in spintronics devices has proven to be noteworthy. Here we demonstrate the efficient control of magnetization dynamics of $\beta$-W/CoFeB bilayer when capped by low SOC organic and inorganic layers. The C$_{60}$ capping layer (CL) significantly enhances the magnetization relaxation process compared to the CuO$_x$ in $\beta$-W/CoFeB/CL heterostructures, while the static magnetic properties remain in-different irrespective of the nature of CL. Interestingly, the spin-orbital to charge conversion phenomenon is found to be enhanced for $\beta$-W/CoFeB/CuO$_x$ stacking compared to the $\beta$-W/CoFeB/C$_{60}$ heterostructure, signifying the anti-correlation between the magnetic damping and spin-orbital to charge conversion. The results are interpreted by the interfacial phenomena, like the orbital Rashba effect, two-magnon scattering, and interfacial spin memory loss. Our detailed experimental investigations shed light on the importance of low SOC materials in effectively tuning the magnetization dynamics for the development of future power efficient spintronics devices.

cond-mat.mes-hall↗

arXiv2024

Efficient spin to charge conversion and spin memory loss mitigation in oriented $\text{RuO}_2$ films

$\text{RuO}_2$, a transition metal oxide, is attracting attention in spintronics for its unique altermagnetic properties, which influence spin currents. Its ability to produce large spin-orbit torques and spin Hall effects is key for energy-efficient magnetic memory and logic devices. Additionally, the tunable thickness and crystallinity of $\text{RuO}_2$ thin films optimize torque efficiency for low-power switching. Spin pumping, a versatile method for investigating spin dynamics in $\text{RuO}_2$ thin films, has garnered considerable interest because of its straightforward, non-invasive and uncomplicated approach to addressing impedance mismatch and direct measurement of spintronic parameters. Here we present a systematic and detailed analysis on the efficient spin to charge conversion in (110)-oriented $\text{RuO}_2$ films with amorphous CoFeB as spin source. The spin Hall angle, and spin diffusion length were estimated to be 0.14 $\pm$ 0.01 and 4.58 $\pm$ 0.40 nm, respectively. The spin Hall conductivity of 998.89 $\pm$ 58.23 $\hbar \cdot \frac{Ω^{-1} \, \text{cm}^{-1}}{e}$ has been estimated which is theoretically predicted to be of the similar order. The interfacial spin transparency has been achieved to be 90%. We have shown that the spin memory loss at the $\text{RuO}_2$/CoFeB interface is 15%, which is very small.

cond-mat.mtrl-sci↗

arXiv2024

Origin of unexpected weak Gilbert damping in the LSMO/Pt bilayer system

This study presents a first-principles and semiclassical analysis of the puzzling observation that a La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) thin film exhibits larger Gilbert damping than an LSMO/Pt bilayer, contrary to conventional spin-pumping expectations. Density functional theory with Wannier interpolation yields an intrinsic damping of $\alpha_{\mathrm{int}}^{\mathrm{LSMO}}\!\approx\!1.4\times10^{-3}$, supporting an extrinsic origin of the high experimental value. Guided by the self-induced inverse spin Hall effect (ISHE) demonstrated in LSMO [Gupta et al., Phys.Rev. B 109, 014437 (2024)], we argue that the large spin Hall angle $|\theta_{\mathrm{SH}}|\simeq 0.093$ and low longitudinal conductivity of LSMO enable an efficient conversion of spin current to charge current boosting the effective damping. In the LSMO/Pt heterostructure the Pt cap shunts the charge current, raising $\sigma_{xx}$ and reducing the interfacial $|\theta_{\mathrm{SH}}|$ to~0.007. A Valet-Fert analysis for layer-resolved ab-initio spin accumulation gives the Pt spin-diffusion length and a non-negligible antidamping SOT coefficient, qualitatively accounting for the observed damping reduction under current bias. The seemingly anomalous damping hierarchy is thus reconciled without invoking additional interfacial mechanisms. The distinct length scales governing spin-pumping normalization, namely, the short absorption depth relevant to self-pumping in a single LSMO film versus the full magnetic thickness applicable to an LSMO/Pt bilayer, are crucial in this context. This observation suggests a practical design strategy: by simultaneously tuning the spin Hall-to-longitudinal conductivity ratio and the spin-diffusion length, one can engineer heterostructures with minimized magnetic losses for spin-orbitronics applications.

cond-mat.mtrl-sci↗

arXiv2024

Dependence of Exchange Bias on Interparticle Interactions in Co/CoO Core/shell Nanostructures

This article reports dependence of exchange bias (EB) effect on interparticle interactions in nanocrystalline Co/CoO core/shell structures, synthesized using conventional sol-gel technique. Analysis via powder X-Ray diffraction (PXRD) studies and transmission electron microscope (TEM) images confirm absence of crystalline phases other than core-shell Co-CoO with average particle size $\approx$18 nm. Volume fraction ($φ$) is varied (from 20\% to 1\%) by introduction of stoichiometric amount of non-magnetic amorphous silica matrix (SiO$_2$) which leads to a change in interparticle separation/interaction. The influence of exchange and dipolar interactions on the EB effect, caused by the variation in interparticle interaction/separation is studied for a series of Co/CoO core/shell nanoparticle systems. Studies of thermal variation of magnetization ($M- T$) and magnetic hysteresis loops ($M- H$) for the series point towards strong dependence of magnetic properties on dipolar interaction in concentrated assemblies whereas individual nanoparticle response is dominant in isolated nanoparticle systems. The analysis of the EB effect reveals a monotonic increase of coercivity ($H_C$) and EB field ($H_E$) with increasing volume fraction. When the nanoparticles are close enough and the interparticle interaction is significant, collective behavior leads to an increase in the effective antiferromagnetic (AFM) CoO shell thickness which results in high $H_C$, $H_E$. Moreover, in concentrated assemblies, the dipolar field superposes to the local exchange field and enhances the EB effect contributing as an additional source of unidirectional anisotropy.

cond-mat.mtrl-sci↗

arXiv2024

Tailoring the Topological Hall Effect in Pt/Co/X (X = Ta, Re) thin films

Electron transport combined with magnetism has gained more attention to the spintronics community in the last few decades. Among them, the topological Hall effect (THE), which arises due to the emergent magnetic field of a non-trivial object, is found to be a promising tool for probing the presence of skyrmions. A sizeable Dzyaloshinskii-Moriya interfacial interaction (iDMI) with reduced effective anisotropy can stabilize skyrmions in thin films. Recently, a large iDMI has been predicted in Pt/Co/Re thin film. Here, we investigate the influence of various magnetic interactions on the THE in perpendicularly magnetized Pt/Co/X (X = Ta, Re) thin films. The presence of skyrmions is confirmed via THE and magnetic force microscope (MFM) imaging. Notably, two distinct types of THE signals are observed in the different samples, which are explained using micromagnetic simulations. Our results reveal that exchange interaction, iDMI, effective anisotropy, and saturation magnetization contribute significantly in determining the variations in topological Hall resistivity behavior, which arise from different skyrmionic phases. These findings contribute to the development of novel material systems featuring different skyrmionic phases with potential applications in spintronics.

cond-mat.mtrl-sci↗

arXiv2024

Observation of Topological Hall Effect and Skyrmions in Pt/Co/Ir/Co/Pt System

The interlayer exchange coupling (IEC) between two ferromagnetic (FM) layers separated by a non-magnetic (NM) spacer layer gives rise to different types of coupling with the variation of spacer layer thickness. When the NM is metallic, the IEC is attributed to the well known Ruderman Kittel Kasuya Yosida (RKKY) interaction which shows an oscillatory decaying nature with increasing thickness. Due to this, it is possible to tune the coupling between the two FM to be either ferromagnetic or antiferromagnetic. In this work we have studied a Pt/Co/Ir/Co/Pt system where the Co thickness has been taken in the strong perpendicular magnetic anisotropy regime which is much less than the spin reorientation transition thickness. By tuning the Ir thickness to 2.0 nm, a canted state of magnetization reversal in the system is observed which gives rise to a possibility of nucleating topologically non trivial spin textures like skyrmions. Further, with the combination of transport and magnetic force microscopy (MFM) measurements, we have confirmed the presence of skyrmions in our system. These findings may be useful for potential applications in emerging spintronic and data storage technologies using skyrmions.

cond-mat.mtrl-sci↗

arXiv2024

Magnon mediated spin pumping by coupled ferrimagnetic garnets heterostructure

Spin pumping has significant implications for spintronics, providing a mechanism to manipulate and transport spins for information processing. Understanding and harnessing spin currents through spin pumping is critical for the development of efficient spintronic devices. The use of a magnetic insulator with low damping, enhances the signal-to-noise ratio in crucial experiments such as spin-torque ferromagnetic resonance (FMR) and spin pumping. A magnetic insulator coupled with a heavy metal or quantum material offers a more straight forward model system, especially when investigating spin-charge interconversion processes to greater accuracy. This simplicity arises from the absence of unwanted effects caused by conduction electrons unlike in ferromagnetic metals. Here, we investigate the spin pumping in coupled ferrimagnetic (FiM) Y3Fe5O12 (YIG)/Tm3Fe5O12 (TmIG) bilayers combined with heavy-metal (Pt) using the inverse spin Hall effect (ISHE). It is observed that magnon transmission occurs at both of the FiMs FMR positions. The enhancement of spin pumping voltage (Vsp) in the FiM garnet heterostructures is attributed to the strong interfacial exchange coupling between FiMs. The modulation of Vsp is achieved by tuning the bilayer structure. Further, the spin mixing conductance for these coupled systems is found to be 10^18 m^-2. Our findings describe a novel coupled FiM system for the investigation of magnon coupling providing new prospects for magnonic devices.

cond-mat.mtrl-sci↗

arXiv2024

Efficient Control of Magnetization Dynamics Via W/CuO$_\text{x}$ Interface

Magnetization dynamics, which determine the speed of magnetization switching and spin information propagation, play a central role in modern spintronics. Gaining its control will satisfy the different needs of various spintronic devices. In this work, we demonstrate that the surface oxidized Cu (CuO$_\text{x}$) can be employed for the tunability of magnetization dynamics of ferromagnet (FM)/heavy metal (HM) bilayer system. The capping CuO$_\text{x}$ layer in CoFeB/W/CuO$_\text{x}$ trilayer reduces the magnetic damping value in comparison with the CoFeB/W bilayer. The magnetic damping even becomes lower than that of the CoFeB/CuO$_\text{x}$ by ~ 16% inferring the stabilization of anti-damping phenomena. Further, the reduction in damping is accompanied by a very small reduction in the spin pumping-induced output DC voltage in the CoFeB/W/CuO$_\text{x}$ trilayer. The simultaneous observation of anti-damping and spin-to-charge conversion can be attributed to the orbital Rashba effect observed at the HM/CuO$_\text{x}$ interface. Our experimental findings illustrate that the cost-effective CuO$_\text{x}$ can be employed as an integral part of modern spintronics devices owing to its rich underneath spin-orbital physics.

cond-mat.mtrl-sci↗

arXiv2023

Structural deformation and irreversible magnetic properties of flexible Co/Pt and Co/Pd thin films

The successful commercialization of flexible spintronic devices requires a complete understanding of the impact of external strain on the structural, electronic, and magnetic properties of a system. The impact of bending-induced strain on flexible films is studied quite well. However, little is known about the effect of other modes of flexibility, e.g., wrinkling, twisting, peeling, and stretching on the functional properties of flexible films. In this context, perpendicular magnetic anisotropic Co/Pt and Co/Pd thin films are prepared on flexible Kapton substrates, and the impact of the peeling mode is studied in detail. The peeling method generates numerous cracks, and buckling in the thin film, along with localized blister formation imaged by scanning electron microscopy. Further, the resistivity measurement confirms a significant enhancement in sample resistance owing to the severe damage of the films. The structural discontinuities strongly affect the magnetization reversal phenomena as measured by the magneto-optic Kerr effect (MOKE)-based microscopy. The bubble domains got converted to elongated-shaped domains due to several hindrances to the wall motion after strain application. Further, the relaxation measurements reveal that the thermal energy is insufficient to switch the magnetization at a few areas due to their high pinning potential associated with the damages. In contrast to bending-induced strain, here, all the modifications in the functional properties are found to be irreversible in nature.

cond-mat.mtrl-sci↗

arXiv2023

Molecular Hybridization Induced Antidamping and Sizable Enhanced Spin-to-Charge Conversion in Co20Fe60B20/$β$-W/C60 Heterostructures

Development of power efficient spintronics devices has been the compelling need in the post-CMOS technology era. The effective tunability of spin-orbit-coupling (SOC) in bulk and at the interfaces of hybrid materials stacking is a prerequisite for scaling down the dimension and power consumption of these devices. In this work, we demonstrate the strong chemisorption of C60 molecules when grown on the high SOC $β$-W layer. The parent CFB/$β$-W bilayer exhibits large spin-to-charge interconversion efficiency, which can be ascribed to the interfacial SOC observed at the Ferromagnet/Heavy metal interface. Further, the adsorption of C60 molecules on $β$-W reduces the effective Gilbert damping by $\sim$15% in the CFB/$β$-W/C60 heterostructures. The anti-damping is accompanied by a gigantic $\sim$115% enhancement in the spin-pumping induced output voltage owing to the molecular hybridization. The non-collinear Density Functional Theory calculations confirm the long-range enhancement of SOC of $β$-W upon the chemisorption of C60 molecules, which in turn can also enhance the SOC at the CFB/$β$-W interface in CFB/$β$-W/C60 heterostructures. The combined amplification of bulk as well interfacial SOC upon molecular hybridization stabilizes the anti-damping and enhanced spin-to-charge conversion, which can pave the way for the fabrication of power efficient spintronics devices.

cond-mat.mtrl-sci↗

arXiv2023

Spinterface Mediated Magnetic Properties of Co20Fe60B20/Alq3 Heterostructures

Organic semiconductors (OSCs) are suitable materials for spintronics applications as they form a spinterface when placed next to a ferromagnet, which in turn leads to novel functionalities. The evolution of spinterface can tune the global magnetic anisotropy, magnetization reversal, magnetization dynamics, etc. Planar tris-(8-hydroxyquinoline)aluminum (Alq3) OSC has shown tremendous potential for spintronics applications, thanks to its efficient spin-polarized current transport ability. Here, we establish the spinterface when the Alq3 molecules are deposited on amorphous ferromagnet Co20Fe60B20(CFB). The $π$-d hybridization in CFB/Alq3 enhances the coercive field and significantly modifies the shape and size of the magnetic domains. A $\sim$100% increase in uniaxial anisotropic energies and a reduction in magnetic damping are also evident owing to the strong interfacial hybridization.

cond-mat.mtrl-sci↗

arXiv2023

Self-induced inverse spin Hall effect in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ films

The efficient generation of spin currents and spin torques via spin-orbit coupling is an important goal of spintronics research. One crucial metric for spin current generation is the spin Hall angle, which is the ratio of the spin Hall current to the transversely flowing charge current. A typical approach to measure the spin Hall angle in nonmagnetic materials is to generate spin currents via spin pumping in an adjacent ferromagnetic layer and measure the transverse voltage from the inverse spin Hall effect in the nonmagnetic layer. However, given that the spin Hall effect also occurs in ferromagnets, single ferromagnetic layers could generate a self-induced transverse voltage during spin pumping as well. Here we show that manganite based La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) films deposited by pulsed laser deposition exhibit a significant self-induced inverse spin Hall voltage while undergoing spin pumping. We observe efficient spin to charge conversion in the LSMO films via the inverse spin Hall effect. A spin pumping voltage of 1.86 $μ$V is observed in the LSMO (12 nm) film. Using density functional theory and the Kubo formalism, we calculate the intrinsic spin current conductivities of these films and show that they are in reasonable agreement with the experimental measurements.

physics.app-ph↗