Research Projects

Emerging Spin-orbitronics device concepts of magnetic memory and logic application requires fundamental understanding of the mechanism involved in reciprocal charge to spin current interconversion. Amongst various challenges that such application faces, the spin torque required for energy efficient magnetization switching and driving domain wall with large velocity have drawn intense attention due to interesting physics and its relevance in spin-orbitronics devices. To harness the full potential of spin-orbitronics devices beyond Complementary Metal Oxide Semiconductor technologies, it is pertinent to have sufficiently large efficiency of charge-spin current interconversion and vice-versa. Though both charge current to spin current conversion as well as spin current to charge current conversion has been discussed by various groups in different stacks separately, to the best of our knowledge its reciprocal/non-reciprocal nature in wide variety of heterostructures remain elusive. Another challenging aspect is to understand the role of interface electronic structure and transparency of interface in the reciprocity of interconversion between spin current and charge current in technologically relevant ferromagnetic thin film heterostructures. It is worth mentioning here that these interfacial effects are intricately related to the hybridization at the interface and show their imprint on the effective Gilbert damping of the stack. We aim to address these contemporary problems of modern spintronics research within this project. We plan to perform experimental and theoretical studies in HM/FM based heterostructures which will lead to the solid understanding of mechanisms involved during the interconversion of charge current to spin current. We will aim to achieve high transparency for both spin as well as charge transfer across the interface in such bilayers which may make these heterostructures as key materials for application in spin orbitronics devices. In particular, we will attempt to achieve reciprocal charge to spin current conversion in interface engineered heavy metal (Ta,W)/Ferromagnet (CoFe, CoFeB) based heterostructures. Interface engineering will be done by doping Nitrogen or Oxygen in the HM layer as well as by incorporating Cu or Cr as dusting layer in the stack. Such modification of the interface is expected to create Rashba like interfaces which in-turn will promote the locking between momentum and direction of the spin polarization. Furthermore, effective Gilbert damping parameter will be investigated using spin-torque ferromagnetic resonance set up as a function of HM layer and FM layer thickness. Using harmonic Hall voltage measurement charge current to spin current conversion efficiency will be quantified. Furthermore, spin pumping and inverse spin Hall effect measurement will be performed to obtain the estimate of spin current to charge current conversion efficiency. In these stacks interface electronic structure will be investigated using x-ray photoelectron spectroscopy. Also, using time of flight secondary ion mass spectroscopy layer by layer etching will be performed to understand the precise atomic composition of a layer. These studies are expected to provide in-depth insight into the role of bulk and interface states in governing either reciprocal or non-reciprocal charge-spin interconversion. In case of stacks exhibiting the non-reciprocal nature, attempts will be made to identify the source of charge or spin leakage and minimize such loss. As Ta/CoFeB based stacks is an important constituent of magnetic recording industry, we believe such studies is critical for the development of next generation spin-orbitronics devices.