arXiv subjects

Akanksha Chouhan

Publications and source records attributed to Akanksha Chouhan.

4 recordsLinked to original sources

arXiv2026

Reciprocity of Charge-Orbital-Spin Transport in Normal-Metal/Ferromagnet Heterostructures

Orbital angular momentum has recently emerged as an important carrier of angular momentum in solids, offering new pathways for spin orbitronic functionality beyond conventional spin transport. Here, we investigate the orbital Hall effect which generates orbital torques and their reciprocal process viz orbital pumping and the inverse orbital Hall effect (iOHE) in non-magnet/ferromagnet heterostructures. Using two port scattering parameter measurements on Ru/Ni, Ru/Pt/CoFeB and Co/Cu/SiO2 devices, we directly probe both orbital torque driven magnetization dynamics and orbital pumping within the same device platform. We observe that the transmission coefficients satisfy the symmetry relations required by Onsager reciprocity, demonstrating reciprocal conversion between charge, orbital and spin angular momenta. Our results establish orbital pumping as the reciprocal counterpart of orbital torque. Our experimental findings provide a unified framework for orbital transport phenomena.

cond-mat.mes-hall↗

arXiv2025

Out-of-plane angle resolved second harmonic Hall analysis in perpendicular magnetic anisotropy systems

Spin orbit torques (SOT) are used to manipulate magnetization of ferromagnets in heavy metal / ferromagnetic bilayers and thus are technologically relevant from magnetization switching perspective. This necessitates development of methods which give an insight into SOT behaviour and enable SOT efficiency estimation. In this article, we demonstrate an experimental approach of out-of-plane (OOP) angle resolved Second Harmonic Hall (SHH) measurement, in Pt/Co and Ta/CoFeB perpendicular magnetic anisotropy (PMA) systems, for damping-like and field-like SOT efficiency estimation. This method reveals a unique anomalous field-like torque dependent on magnetization direction in Ta/CoFeB system. The damping-like and field-like SOT efficiencies are extracted by solving LLGS equation in the low frequency limit of magnetic susceptibility. Along with SHH measurements, we also experimentally demonstrate anomalous Hall effect (AHE) based spin-torque ferromagnetic resonance (STFMR) technique for SOT efficiency quantification in PMA systems.

cond-mat.mes-hall↗

arXiv2025

Gate Voltage-Controlled Magnetic Anisotropy Effect on Pt-Porphyrin functionalized single-layer graphene

We report a novel approach to engineering large voltage-controlled magnetic anisotropy (VCMA) and enhanced spin-orbit coupling (SOC) at the interface of single-layer graphene (SLG) and NiFe (Py) through non-covalent functionalization with Platinum (II) 5,10,15,20-tetraphenyl porphyrin (Pt-porphyrin). Using chemical vapor deposition (CVD)-grown SLG, we demonstrate that Pt-porphyrin functionalization significantly increases the SOC and enables robust voltage modulation of interfacial magnetic anisotropy, as confirmed by spin-torque ferromagnetic resonance (ST-FMR) measurements. A substantial VCMA coefficient of 375.6 (fJ/(V-m)) is achieved, accompanied by an order-of-magnitude enhancement in spin torque efficiency (θsh) compared to pristine SLG. The resonance field exhibits a clear, reversible shift under applied gate voltage, confirming robust electric-field modulation of interfacial magnetic anisotropy. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) confirm the structural integrity and effective charge transfer at the functionalized interface. Electrical characterization of back-gated graphene field-effect transistors (GFETs) further reveals tunable electronic properties upon functionalization. Our results establish functionalized graphene/ferromagnet interfaces as a promising platform for low-power, voltage-controlled spintronic devices, paving the way for scalable, energy-efficient memory and logic technologies

cond-mat.mes-hall↗

arXiv2025

Shape Anisotropy Enabled Field Free Switching of Perpendicular Nanomagnets

Spin Orbit Torque-Magnetic Random Access Memory (SOT-MRAM) is being developed as a successor to the Spin transfer torque MRAM (STT-MRAM) owing to its superior performance on the metrics of reliability and read-write speed. SOT switching of perpendicularly magnetized ferromagnet in the heavy metal/ferromagnet bilayer of SOT-MRAM unit cell requires an additional external magnetic field to support the spin-orbit torque generated by heavy metal to cause deterministic switching. This complexity can be overcome if an internal field can be generated to break the switching symmetry. We experimentally demonstrate that by engineering the shape of ferromagnet, an internal magnetic field capable of breaking the switching symmetry can be generated, which allows for deterministic switching by spin-orbit torques. We fabricated nanomagnets of Cobalt with triangular shape on top of Platinum and showed external magnetic field free switching between the two stable states of magnetization by application of nano-second voltage pulses. The experimental findings are consistent with the micro-magnetic simulation results of the proposed geometry.

cond-mat.mes-hall↗