arXiv subjects

Jyotirmoy Chatterjee

Publications and source records attributed to Jyotirmoy Chatterjee.

4 recordsLinked to original sources

arXiv2026

Synaptic Multi-Weight Wafer-Scale Domain Wall Magnetic Tunnel Junctions Driven by Spin Orbit Torque

Spintronic synaptic devices based on magnetic random access memory (MRAM) are a rapidly evolving class within the analog neuromorphic architecture. However, obtaining the multi-weight or analog behavior desired for improved neural network inference accuracy in scaled MRAM remains a challenge. In this study, we demonstrate and tune up to eight distinct resistance levels in 300 mm wafer-scale magnetic tunnel junction artificial synapses driven by spin orbit torque. By varying the applied in-plane field, multi-weight resistance states emerge through domain wall nucleation and pinning. These multi-weight states appear stochastically and can be addressed with an iterative programming algorithm to program a specific resistance. Electromagnetic simulations indicate the multiple states are due to domain wall nucleation mediated by in-plane field and applied voltage. Implementation of the measured multi-weight devices in a neural network yields a 96.1% inference accuracy using the MNIST dataset if all devices provide the same number of multi-weight states. When experimental device-to-device variation is included, the accuracy is 48.6%. Overall, this work demonstrates a route towards multi-weight artificial synapse MRAM, establishing a path towards scalable neuromorphic systems based on spintronics.

cond-mat.mes-hall↗

arXiv2023

Deep Learning based Skin-layer Segmentation for Characterizing Cutaneous Wounds from Optical Coherence Tomography Images

Optical coherence tomography (OCT) is a medical imaging modality that allows us to probe deeper substructures of skin. The state-of-the-art wound care prediction and monitoring methods are based on visual evaluation and focus on surface information. However, research studies have shown that sub-surface information of the wound is critical for understanding the wound healing progression. This work demonstrated the use of OCT as an effective imaging tool for objective and non-invasive assessments of wound severity, the potential for healing, and healing progress by measuring the optical characteristics of skin components. We have demonstrated the efficacy of OCT in studying wound healing progress in vivo small animal models. Automated analysis of OCT datasets poses multiple challenges, such as limitations in the training dataset size, variation in data distribution induced by uncertainties in sample quality and experiment conditions. We have employed a U-Net-based model for the segmentation of skin layers based on OCT images and to study epithelial and regenerated tissue thickness wound closure dynamics and thus quantify the progression of wound healing. In the experimental evaluation of the OCT skin image datasets, we achieved the objective of skin layer segmentation with an average intersection over union (IOU) of 0.9234. The results have been corroborated using gold-standard histology images and co-validated using inputs from pathologists. Clinical Relevance: To monitor wound healing progression without disrupting the healing procedure by superficial, noninvasive means via the identification of pixel characteristics of individual layers.

eess.IV↗

arXiv2023

Analysis of ultrafast magnetization switching dynamics in exchange-coupled ferromagnet-ferrimagnet heterostructures

Magnetization switching in ferromagnets has so far been limited to the current-induced spin-orbit-torque effects. Recent observation of helicity-independent all-optical magnetization switching in exchange-coupled ferromagnet ferrimagnet heterostructures expanded the range and applicability of such ultrafast heat-driven magnetization switching. Here we report the element-resolved switching dynamics of such an exchange-coupled system, using a modified microscopic three-temperature model. We have studied the effect of i) the Curie temperature of the ferromagnet, ii) ferrimagnet composition, iii) the long-range RKKY exchange-coupling strength, and iv) the absorbed optical energy on the element-specific time-resolved magnetization dynamics. The phase-space of magnetization illustrates how the RKKY coupling strength and the absorbed optical energy influence the switching time. Our analysis demonstrates that the threshold switching energy depends on the composition of the ferrimagnet and the switching time depends on the Curie temperature of the ferromagnet as well as RKKY coupling strength. This simulation anticipates new insights into developing faster and more energy-efficient spintronics devices.

cond-mat.mtrl-sci↗

arXiv2022

Optical Switching in Tb/Co-Multilayer Based Nanoscale Magnetic Tunnel Junctions

Magnetic tunnel junctions (MTJs) are elementary units of magnetic memory devices. For high-speed and low-power data storage and processing applications, fast reversal by an ultrashort laser pulse is extremely important. We demonstrate optical switching of Tb/Comultilayer-based nanoscale MTJs by combining optical writing and electrical read-out methods. A 90 fs-long laser pulse switches the magnetization of the storage layer (SL). The change in magnetoresistance between the SL and a reference layer (RL) is probed electrically across the tunnel barrier. Single-shot switching is demonstrated by varying the cell diameter from 300 nm to 20 nm. The anisotropy, magnetostatic coupling, and switching probability exhibit cell-size dependence. By suitable association of laser fluence and magnetic field, successive commutation between high-resistance and low-resistance states is achieved. The switching dynamics in a continuous film is probed with the magneto-optical Kerr effect technique. Our experimental findings provide strong support for the growing interest in ultrafast spintronic devices.

physics.app-ph↗