arXiv subjects

Subhakanta Das

Publications and source records attributed to Subhakanta Das.

6 recordsLinked to original sources

arXiv2026

Strain effects in [001] textured Co80Ir20 thin films with negative magnetocrystalline anisotropy

Co80Ir20 ferromagnetic thin films have recently been the focus of intensive research because the negative magnetocrystalline anisotropy adds to the shape anisotropy and favors a strong alignment of the magnetization in the film plane for [001] textured or epitaxial thin films. However, the role of magnetoelastic effects has not been properly considered in most published research. In this work we have performed a detailed analysis of 24 nm Co80Ir20 thin films deposited on Si/SiO2 with different underlayers (Ta, Pt) and overlayers in order to induce [001]-textured growth and different degrees of strain. Using x-ray diffraction measurements we have found that the c-axis lattice parameter depends on the underlayer material (larger negative strain for Ta), but the degree of texture and the average grain size remain essentially constant, except for one of the multilayers. Differences in the magnetic behavior according to the underlayer were also found in room temperature magnetization vs field loops and temperature dependent dc magnetization measurements. Anisotropy was quantified using ferromagnetic resonance which showed that the effective anisotropy field is also dependent on the underlayer. Ta underlayers show an anisotropy close to that expected for shape, while Pt underlayer induces an additional in-plane anisotropy field of the order of 7-9 kOe. A simple model of stress induced anisotropy gives anisotropy field values similar to those observed experimentally. The correlation between observed strain and anisotropy together with the similarity in microstructural properties strongly suggests that stress effects cannot be disregarded when analyzing the magnetic data for the estimation of the magnetocrystalline contribution.

cond-mat.mtrl-sci↗

arXiv2026

Synergy of fivefold boost SOT efficiency and field-free magnetization switching with broken inversion symmetry: Toward neuromorphic computing

Non-volatile Neuromorphic Computing (NC) elements utilizing Spin Orbit Torque (SOT) provide a viable solution to alleviate the memory wall bottleneck in contemporary computing systems. However, the two challenges, low SOT efficiency and the need for in plane symmetry breaking field for perpendicular magnetization switching, greatly limit its practical implementation. In this work, the enhanced SOT efficiency of Platinum (Pt) SOT layer and field free perpendicular magnetization switching are achieved by integrating thin Ruthenium Oxide (RuO2) layer in our material stack. The optimal RuO2 thickness (0.5 nm) enhances 5.2 times Damping Like (DL) SOT efficiency compared with pure SOT layer (Pt), as determined by hysteresis loop shift measurements, with a relatively low resistivity (90 micro-Ohm-cm). Moreover, we achieve 3 times reduction of critical magnetization switching current density compared to reference sample. Our experimental findings also demonstrate Rashba-induced substantial field-free magnetization switching in the presence of an emergent built-in interfacial field. Notably, reliable multi resistance synaptic states are achieved by tailoring the synergistic effects of enhanced SOT and interfacial magnetism. The functionality of synaptic states has been further evaluated by implementing an artificial neural network and achieved image recognition accuracies of approximately 95% and 87% on the MNIST and Fashion-MNIST datasets, respectively. This systematic study paves the way to energy-efficient, field-free SOT synapses for practical NC applications.

cond-mat.mes-hall↗

arXiv2025

Giant Damping-like Torque Efficiency via Synergistic Spin Hall and enhanced Orbital Hall Effects

Current-induced spin-orbit torque (SOT) has emerged as a promising method for achieving energy-efficient magnetisation switching in advanced spintronic devices. Over the past two decades, researchers have primarily focused on enhancing spin current generation through the spin Hall effect, relying predominantly on the spin degree of freedom (DoF) of the electron, while neglecting its orbital counterpart. Orbital Hall effect depends critically on the crystallinity and the interface between the orbital Hall layer and the orbital-to-spin conversion layer. However, most experimental works on orbital Hall effect relied on polycrystalline films with no special attention to improve the crystallographic texture. In this work, we have grown the Ru layer on a NiW seedlayer, which helped to improve the crystallographic texture, thereby enhancing the switching efficiency by over 44%. Such a huge increase in switching efficiency was achieved by (i) improving crystallographic texture and (ii) leveraging both spin and orbital DoFs. Our study underscores the potential for improving the spin-torque efficiency by combining interface engineering, orbital and spin Hall effects to drive next-generation spintronics.

physics.app-ph↗

arXiv2025

Enhanced Spin Pumping and Magnetization dynamics in Ni$_{80}$Fe$_{20}$/MoS$_2$ stack via interface modification

Materials with strong spin orbit coupling (SOC) are essential for realizing spin orbit torque (SOT) based magnetic memory devices. Transition metal dichalcogenides (TMDs) are promising candidates for such appli cations because of their inherently high SOC strength. In this study, we investigate the spin pumping effect at the interface between a monolayer of molybdenum disulfide (ML-MoS$_2$) and Ni$_{80}$Fe$_{20}$ (Py) thin films using broadband ferromagnetic resonance (FMR) spectroscopy. FMR measurements reveal a notable enhancement in the effective Gilbert damping factor for the ML-MoS$_2$/Py (Pt = 0 nm) interface compared to the reference Py thin films, attributed to spin pumping across the ML-MoS$_2$/Py interface. To further quantify spin pumping efficiency, we introduce a high SOC platinum (Pt) interlayer at the ML-MoS$_2$/Py interface and systematically vary its thickness. This allows us to evaluate key spin transport parameters, including the enhancement in the effective Gilbert damping parameter, the effective spin mixing conductance that reflects the transfer of spin angular momentum from Py to ML-MoS$_2$ and the effective spin current density.

physics.app-ph↗

arXiv2025

Magnetic Orbital Hall Effect in Altermagnet RuO$_2$

Orbital angular momentum provides an alternative channel for current-induced magnetization switching beyond conventional spin--orbit coupling. While orbital Hall effects have been observed in several nonmagnetic materials, their manifestation in symmetry-compensated magnetic systems remains unexplored. Here, we report experimental evidence for a magnetic orbital Hall effect in RuO$_2$. In RuO$_2$(101)/Pt/Co heterostructures, we observe a pronounced unconventional torque characterized by a large out-of-plane component, strong crystalline anisotropy, and deterministic field-free switching of a perpendicular ferromagnet over a wide range of RuO$_2$ thicknesses. The torque exhibits a non-monotonic dependence on Pt thickness, reaching a maximum at 1.5~nm, and displays a long-range RuO$_2$ thickness ($t_{\mathrm{RuO}_2}$) dependence that saturates for $t_{\mathrm{RuO}_2}>100~\mathrm{nm}$. These features cannot be reconciled with conventional spin-current mechanisms. Rather, they indicate a magnetic orbital Hall effect in RuO$_2$ that could originate from exchange-induced momentum-dependent band splitting and its interplay with spin--orbit and crystal-field coupling, with the generated orbital current converted into torque in Pt. Our findings establish altermagnets as intrinsic sources of orbital currents and extend orbitronics to symmetry-compensated magnetic systems.

cond-mat.mes-hall↗

arXiv2024

Enhancement of spin current to charge current conversion in Ferromagnet/Graphene interface

The use of graphene in spintronic devices is contingent on its ability to convert a spin current into a charge current. We have systematically investigated the spin pumping induced spin-to-charge current conversion at the Graphene/FM interface and the effect of interface modification through high spin orbit coupling (SOC) material (Pt) as an interlayer (IL) of varying thicknesses by using broadband FMR spectroscopy. The spin mixing conductance is enhanced from $1.66 \times 10^{18}$ m$^{-2}$ to $2.72 \times 10^{18}$ m$^{-2}$ whereas the spin current density is enhanced from 0.135$\pm $0.003 to 0.242$\pm$0.004 MA/m$^{2}$ at the Graphene/FM interface due to the interface modification using high SOC material Pt as an interlayer. The spin current to charge current conversion efficiency turns out to be $\approx 0.003$ nm for the Graphene/FM interface. These findings support the idea that Graphene in combination with high SOC material (Pt) could be a potential candidate for spintronic applications, specifically for spin-torque-based memory applications.

cond-mat.mes-hall↗