Sudip Majumder

S.N. Bose National Centre for Basic Sciences

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Anjan Barman

S.N. Bose National Centre for Basic Sciences

Samiran Choudhury

S.N. Bose National Centre for Basic Sciences

Y. Otani

The University of Tokyo

Surya Narayan Panda

Chitkara University

Saswati Barman

University of Engineering & Management

Supriyo Bandyopadhyay

Virginia Commonwealth University

Soma Dutta

S.N. Bose National Centre for Basic Sciences

Arpan Bhattacharyya

Indian Institute of Technology Gandhinagar

Sourav Sahoo

S.N. Bose National Centre for Basic Sciences

Sumona Sinha

S.N. Bose National Centre for Basic Sciences

Cooperative Institutions

S.N. Bose National Centre for Basic Sciences

Virginia Commonwealth University

University of Illinois Chicago

The University of Tokyo

RIKEN

Saha Institute of Nuclear Physics

Indian Association for the Cultivation of Science

KIIT University

Lawrence Berkeley National Laboratory

Washington State University Vancouver

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Bias field orientation driven reconfigurable magnonics and magnon−magnon coupling in triangular shaped Ni₈₀Fe₂₀ nanodot arrays

Nanotechnology (2022)

Amrit Kumar Mondal Sudip Majumder Bipul Kumar Mahato Saswati Barman Y. Otani

Reconfigurable magnonics have attracted intense interest due to their myriad advantages including energy efficiency, easy tunability and miniaturization of on-chip data communication and processing devices. Here, we demonstrate efficient reconfigurability of spin-wave (SW) dynamics as well as SW avoided crossing by varying bias magnetic field orientation in triangular shaped Ni80Fe20nanodot arrays. In particular, for a range of in-plane angles of bias field, we achieve mutual coherence between two lower frequency modes leading to a drastic modification in the ferromagnetic resonance frequency. Significant modification in magnetic stray field distribution is observed at the avoided crossing regime due to anisotropic dipolar interaction between two neighbouring dots. Furthermore, using micromagnetic simulations we demonstrate that the hybrid SW modes propagate longer through an array as opposed to the non-interacting modes present in this system, indicating the possibility of coherent energy transfer of hybrid magnon modes. This result paves the way for the development of integrated on-chip magnonic devices operating in the gigahertz frequency regime.

Magnonics

Magnon

Reconfigurability

Nanodot

Spin wave

10.1088/1361-6528/acae5e

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Citations (8)

Defect-Density- and Rashba-Shift-Induced Interfacial Dzyaloshinskii–Moriya Interaction and Spin Pumping in Single-Layer Graphene/Co₂₀Fe₆₀B₂₀ Heterostructures: Implications for New-Generation Spintronics

ACS Applied Nano Materials (2022)

Amrit Kumar Mondal Sudip Majumder Sourav Sahoo Surya Narayan Panda Sumona Sinha

The quest for quantum phenomena in unconventional materials has led to the development of myriad unique systems. Because of their unusual atomic-scale interface properties and their controllability, graphene/ferromagnet heterostructures have emerged as a strong contender for next-generation spintronics. Further development demands superior properties and correlation between the different microscopic mechanisms involved. Herein, we demonstrate a superior interfacial Dzyaloshinskii–Moriya interaction (iDMI) in single-layer graphene/CoFeB/SiO2 heterostructures from asymmetric spin-wave dispersion measurement using a Brillouin light-scattering technique. The spin-wave frequencies and line widths have been correlated with structural and nanoscale morphological properties to evaluate the roles of Rashba shift and defect density for the emergence of iDMI and spin pumping for a range of thicknesses of the CoFeB layer, where the defects have been found to play a dominant role for the extrinsic spin–orbit coupling over the Rashba shift. A significantly large iDMI and spin-mixing conductance have been observed even at moderately low Ar pressure during sputter deposition of the ferromagnetic layer, which asserts further optimization of the said properties with external deposition parameters for application in next-generation energy-efficient and miniaturized spintronic and spin–orbitronic devices.

10.1021/acsanm.2c00098

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Citations (8)

Tunable Strong Magnon-Magnon Coupling in Two-Dimensional Array of Diamond Shaped Ferromagnetic Nanodots

Physica Scripta (2023)

Sudip Majumder Samiran Choudhury Saswati Barman Y. Otani Anjan Barman

Abstract Hybrid magnonics involving coupling between magnons and different quantum particles have been extensively studied during past few years for varied interests including quantum electrodynamics. In such systems, magnons in magnetic materials with high spin density are utilized where the ‘coupling strength’ is collectively enhanced by the square root of the number of spins to overcome the weaker coupling between individual spins and the microwave field. However, achievement of strong magnon-magnon coupling in a confined nanomagnets would be essential for on-chip integration of such hybrid systems. Here, through intensive study of interaction between different magnon modes in a Ni 80 Fe 20 (Py) nanodot array, we demonstrate that the intermodal coupling can approach the strong coupling regime with coupling strength up to 0.82 GHz and cooperativity of 2.51. Micromagnetic Simulations reveal that anticrossing occurs due to change in exchange configuration (symmetry breaking). The coupling strength could be continuously tuned by varying the bias field ( H ext ) strength and orientation ( ϕ ), opening routes for external control over hybrid magnonic systems. These findings could greatly enrich the rapidly evolving field of quantum magnonics.

Magnon

Magnonics

Nanodot

10.1088/1402-4896/ad1953

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Citations (3)

Ultrafast demagnetization and precession in permalloy films with varying thickness

Physical review. B./Physical review. B (2023)

Surya Narayan Panda Sucheta Mondal Sudip Majumder Anjan Barman

Excitation by a femtosecond laser pulse is an efficient method to control various ultrafast spin manipulation processes, e.g., ultrafast demagnetization, remagnetization, and damping. Thus, a comprehensive study of magnetization dynamics over a broad timescale by varying the excitation energy can provide a solid foundation of integrating these processes within a single system. Here, time-resolved magneto-optical Kerr effect magnetometry is used to investigate the evolution of magnetization dynamics from femtosecond- to nanosecond timescale in ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ thin films. The correlation between ultrafast demagnetization time and fast remagnetization time with the laser pump fluence is demonstrated experimentally and is validated by the phenomenological three-temperature modeling involving different coupling parameters and specific heat of electron-, lattice-, and spin baths. Significant enhancement of the Gilbert damping parameter and a redshift in the precessional frequency are observed for uniform Kittel mode and perpendicular standing spin-wave modes with increasing excitation energy. Direct correlation between demagnetization time and Gilbert damping parameter indicates spin-flip scattering as the responsible mechanism for the ultrafast demagnetization and intraband conductivity-like contribution to the damping process. This extensive study develops an in-depth understanding about the role of laser fluence on the ultrafast spin dynamics. Our findings will be beneficial for the construction of ultrahigh-speed spintronics devices which rely on the heat-assisted modification of the dynamic properties in ferromagnetic thin films.

Magnetization dynamics

Permalloy

Spin wave

10.1103/physrevb.108.144421

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Citations (3)

Structural Phase Dependent Giant Interfacial Spin Transparency in W/CoFeB Thin Film Heterostructure

arXiv (Cornell University) (2020)

Surya Narayan Panda Sudip Majumder Arpan Bhattacharyya Soma Dutta Samiran Choudhury

Pure spin current has transfigured the energy-efficient spintronic devices and it has the salient characteristic of transport of the spin angular momentum. Spin pumping is a potent method to generate pure spin current and for its increased efficiency high effective spin-mixing conductance (Geff) and interfacial spin transparency (T) are essential. Here, a giant T is reported in Sub/W(t)/Co20Fe60B20(d)/SiO2(2 nm) heterostructures in \beta-tungsten (\beta-W) phase by employing all-optical time-resolved magneto-optical Kerr effect technique. From the variation of Gilbert damping with W and CoFeB thicknesses, the spin diffusion length of W and spin-mixing conductances are extracted. Subsequently, T is derived as 0.81 \pm 0.03 for the \beta-W/CoFeB interface. A sharp variation of Geff and T with W thickness is observed in consonance with the thickness-dependent structural phase transition and resistivity of W. The spin memory loss and two-magnon scattering effects are found to have negligible contributions to damping modulation as opposed to spin pumping effect which is reconfirmed from the invariance of damping with Cu spacer layer thickness inserted between W and CoFeB. The observation of giant interfacial spin transparency and its strong dependence on crystal structures of W will be important for pure spin current based spin-orbitronic devices.

Spin pumping

Spin diffusion

Source

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Citations (1)

Shape dependent high frequency spin-wave dynamics in nanoscale magnonic crystals

Journal of Magnetism and Magnetic Materials (2019)

Anulekha De Sucheta Mondal Samiran Choudhury Sourav Sahoo Sudip Majumder

Spin wave

Dynamics

10.1016/j.jmmm.2019.165263

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Citations (10)

Structural Phase Dependent Giant Interfacial Spin Transparency in W/CoFeB Thin Film Heterostructure

arXiv (Cornell University) (2020)

Surya Narayan Panda Sudip Majumder Arpan Bhattacharyya Soma Dutta Samiran Choudhury

Spin pumping

Spin diffusion

10.48550/arxiv.2009.14143

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Citations (1)

Active Control of Mode Crossover and Mode Hopping of Spin Waves in a Ferromagnetic Antidot Lattice

Physical Review Applied (2018)

Samiran Choudhury Sudip Majumder Saswati Barman Y. Otani Anjan Barman

Artificially patterned, periodically modulated magnetic media, popularly known as $m\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}g\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c$ $c\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}y\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}s$ (MCs), have attracted much attention for their huge potential in reconfigurable magnetic and spintronic devices. The authors investigate the magnetization dynamics in a two-dimensional MC, a periodic arrangement of divots in a ferromagnetic thin film, achieving active control of spin-wave dynamics at GHz frequencies by varying the strength and orientation of an external magnetic field. This tunability could be crucial to nanoscale, on-chip microwave communication technology.

Spin wave

Lattice (music)

10.1103/physrevapplied.10.064044

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Citations (16)

Active Control of Dipole-Exchange Coupled Magnon Modes in Nanoscale Bicomponent Magnonic Crystals

ACS Applied Nano Materials (2023)

Arundhati Adhikari Sudip Majumder Y. Otani Anjan Barman

Bicomponent magnonic crystals (BMCs) are metasurfaces formed using two dissimilar materials, which offer a richer manipulation of spin waves and promising spin-wave-based computation, communication, and signal processing. Here, the intricate interplay of spin dynamics between two different materials Co50Fe50 and Ni80Fe20 forming a BMC is exploited experimentally. Optimally engineered interface leads to interelement exchange coupling combined with the long-range dipolar coupling as confirmed by micromagnetic simulations. These couplings have been further tuned by systematic variation of the filling fraction of Co50Fe50 and Ni80Fe20 in the BMC. Moreover, the characteristic properties of spin-wave spectra are found to be highly sensitive to the bias-field strength. Further numerical simulations based on experimentally determined parameters demonstrate long-distance and high-speed spin-wave propagation in such BMCs controlled by the filling fraction and offer a diode-like on/off mechanism determined by the applied magnetic field strength. These observations will lead to the development of high-speed reconfigurable magnonic devices controlled by external parameters.

Magnon

Spin wave

Micromagnetics

10.1021/acsanm.2c05441

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Citations (9)

Formation of binary magnon polaron in a two-dimensional artificial magneto-elastic crystal

NPG Asia Materials (2023)

Sudip Majumder Justine L. Drobitch Supriyo Bandyopadhyay Anjan Barman

Abstract We observed strong tripartite magnon-phonon-magnon coupling in a two-dimensional periodic array of magnetostrictive nanomagnets deposited on a piezoelectric substrate, forming a 2D magnetoelastic “crystal”; the coupling occurred between two Kittel-type spin wave (magnon) modes and a (non-Kittel) magnetoelastic spin wave mode caused by a surface acoustic wave (SAW) (phonons). The strongest coupling occurred when the frequencies and wavevectors of the three modes matched, leading to perfect phase matching. We achieved this condition by carefully engineering the frequency of the SAW, the nanomagnet dimensions and the bias magnetic field that determined the frequencies of the two Kittel-type modes. The strong coupling (cooperativity factor exceeding unity) led to the formation of a new quasi-particle, called a binary magnon-polaron, accompanied by nearly complete (~100%) transfer of energy from the magnetoelastic mode to the two Kittel-type modes. This coupling phenomenon exhibited significant anisotropy since the array did not have rotational symmetry in space. The experimental observations were in good agreement with the theoretical simulations.

Magnon

Nanomagnet

10.1038/s41427-023-00499-4

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Citations (2)