Vineeth Mohanan Parakkat
@cusat.ac.in
Assistant Professor at Department of Physics
Cochin University of Science and Technology
His research interests include
• Magnetic thin films, magnetic data storage
• Spintronics: Electrical control of magnetism
• Magnetic metamaterials: Emergent physics in nanomagnetic arrays
• Micromagnetic simulations.
EDUCATION
Dr. Vineeth Mohanan P joined the department of Physics, CUSAT, as Assistant Professor in June 2021. He was working as a postdoctoral scholar at the University of Washington, Seattle, before joining CUSAT. He completed integrated Ph.D. program from the Indian Institute of Science, Bangalore, during 2007-2017. He received a bachelor’s degree in Physics from Kannur University in 2007.
RESEARCH, TEACHING, or OTHER INTERESTS
Condensed Matter Physics, Electronic, Optical and Magnetic Materials, Materials Science, Surfaces, Coatings and Films
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Vineeth Mohanan Parakkat, Gavin M. Macauley, Robert L. Stamps, and Kannan M. Krishnan
American Physical Society (APS)
We demonstrate ground state tunability for a hybrid artificial spin ice composed of Fe nanomagnets which are subject to site-specific exchange-bias fields, applied in integer multiples of the lattice along one sublattice of the classic square artificial spin ice. By varying this period, three distinct magnetic textures are identified: a striped ferromagnetic phase; an antiferromagnetic phase attainable through an external field protocol alone; and an unconventional ground state with magnetically charged pairs embedded in an antiferromagnetic matrix. Monte Carlo simulations support the results of field protocols and demonstrate that the pinning tunes relaxation timescales and their critical behavior.
Vineeth Mohanan Parakkat and Kannan M Krishnan
IOP Publishing
We describe the microfabrication and magnetic behavior of a composite/hybrid, two-dimensional, magnetostatically interacting array of nanomagnets of Fe and exchange-biased bilayer Fe/IrMn heterostructures. Such an interacting array of nanomagnets, forming an artificial spin ice lattice but with a hybrid structure, has not been demonstrated before. These devices are fabricated of epitaxially grown Fe/IrMn thin films by a two-stage electron beam lithography process involving metal mask transfer and controlled ion milling. Following the epitaxial deposition of Fe/IrMn bilayer films, the first step involves electron beam lithography fabrication of nanomagnet arrays, followed by selective removal of exchange-bias by etching away IrMn layer at specific nanomagnet elements by ion milling. The technique described provides a way to apply a site-specific magnetic field at the nanometer length scale, utilizing the phenomenon of exchange-bias, as demonstrated here for an array with local fields applied at twice the period of the artificial spin ice lattice. This technology can also be readily extended to different spintronic devices requiring spatial distribution of exchange-bias fields.
Vineeth Mohanan Parakkat, Kaichen Xie, and Kannan M. Krishnan
American Physical Society (APS)
We describe an artificial spin ice (ASI) composed of exchange biased heterostructured nanomagnetic elements with unidirectional anisotropy and compare it with a conventional ASI constituted by ferromagnets with uniaxial anisotropy (Ising spins). The introduction of a local exchange bias field, aligned along one of the sublattices of the square ASI, lifts the spin-reversal symmetry of the vertices. By varying the lattice constant of the square array, we control the ratio of exchange bias (EB) to dipolar field (${H}_{\\mathrm{EB}}/{H}_{\\mathrm{dip}}$) and tune the ground state from an antiferromagnetic to a ferromagnetic configuration with an effective magnetic moment. The geometric frustration of dipolar interactions is moderated by a nonfrustrated local field, leading to a mesoscopic system with specific metastable states observed during the demagnetization process.
Vineeth Mohanan Parakkat, K. R. Ganesh, and P. S. Anil Kumar
AIP Publishing
The dependence of perpendicular magnetization and Curie temperature (Tc) of Pt/Co/Pt thin films on the thicknesses of Pt seed (Pts) and presence of Ta buffer layer has been investigated in this work. Pt and Co thicknesses were varied between 2 to 8 nm and 0.35 to 1.31 nm (across the spin reorientation transition thickness) respectively and the Tc was measured using SQUID magnetometer. We have observed a systematic dependence of Tc on the thickness of Pts. For 8nm thickness of Pts the Co layer of 0.35nm showed ferromagnetism with perpendicular anisotropy at room temperature. As the thickness of the Pts was decreased to 2nm, the Tc went down below 250K. XRD data indicated polycrystalline growth of Pts on SiO2. On the contrary Ta buffer layer promoted the growth of Pt(111). As a consequence Ta(5nm)/Pt(3nm)/Co(0.35nm)/Pt(2nm) had much higher Tc (above 300K) with perpendicular anisotropy when compared to the same stack without the Ta layer. Thus we could tune the ferromagnetic Tc and anisotropy by varying the Pts thickness and also by introducing Ta buffer layer. We attribute these observations to the micro-structural evolution of Pts layer which hosts the Co layer.
Vineeth Mohanan Parakkat, K. R. Ganesh, and P. S. Anil Kumar
AIP Publishing
The effect of Cu dusting on perpendicular magnetic anisotropy of sputter grown Pt/Co/Pt stack in which the Cu layer is in proximity with that of Co is investigated in this work. We used magneto optic Kerr effect microscopy measurements to study the variation in the reversal mechanisms in films with Co thicknesses below 0.8nm by systematically varying their perpendicular magnetic anisotropy using controlled Cu dusting. Cu dusting was done separately above and below the cobalt layer in order to understand the role of bottom and top Pt layers in magnetization reversal mechanisms of sputtered Pt/Co/Pt stack. The introduction of even 0.3nm thick Cu layer below the cobalt layer drastically affected the perpendicular magnetic anisotropy as evident from the nucleation behavior. On the contrary, even a 4nm thick top Cu layer had little effect on the reversal mechanism. These observations along with magnetization data was used to estimate the role of top and bottom Pt in the origin of perpendicular magnetic anisotropy as well as magnetization switching mechanism in Pt/Co/Pt thin films. Also, with an increase in the bottom Cu dusting from 0.2 to 0.4nm there was an increase in the number of nucleation sites resulting in the transformation of domain wall patterns from a smooth interface type to a finger like one and finally to maze type.
Vineeth Mohanan Parakkat and P. S. Anil Kumar
AIP
Magnon contribution to the resistance of ferromagnetic film like Permalloy is investigated by magnetotransport measurements. We are able to observe and distinguish Anisotropic-Magnetoresistance(AMR)(1) and Magnon Magnetoresistance(MMR)(2) contributions clearly in PLD grown Permalloy films. A linear non-saturating longitudinal MR observed in high field regime for permalloy films could never be explained using AMR but only MMR can account for it.