Samiran Choudhury

Dielectric Relaxations of (Acetamide + Electrolyte) Deep Eutectic Solvents in the Frequency Window, 0.2 ≤ ν/GHz ≤ 50: Anion and Cation Dependence

Dielectric relaxation (DR) measurements in the frequency range 0.2 ≤ ν/GHz ≤ 50 have been carried out for neat molten acetamide and six different (acetamide + electrolyte) deep eutectic solvents (DESs) for investigating ion effects on DR dynamics in these ionic DESs. Electrolytes used are lithium salts of bromide (LiBr), nitrate (LiNO3), and perchlorate (LiClO4); sodium salts of perchlorate (NaClO4) and thiocyante (NaSCN); and potassium thiocyanate (KSCN). With these electrolytes acetamide forms DESs approximately at an 80:20 mol ratio. Simultaneous fits to the measured permittivity (ε′) and loss (ε″) spectra of these DESs at ∼293 K require a sum of four Debye (4-D) processes with relaxation times spread over picosecond to nanosecond regime. In contrast, DR spectra for neat molten acetamide (∼354 K) depict 2-D relaxation with time constants ∼50 ps and ∼5 ps. For both the neat and ionic systems, the undetected dispersion, ε∞ – n(D)2, remains to be ∼3–4. Upon comparison, measured DR dynamics reveal pronounced anion and cation effects. Estimated static dielectric constants (ε0) from fits for these DESs cover the range 12 < ε0 < 30 and are remarkably lower than that (ε0 ∼ 64) measured for molten acetamide at ∼354 K. Hydrodynamic effective rotation volumes (Veff) estimated from the slowest DR relaxation time constants vary with ion identity and are much smaller than the molecular volume of acetamide. This decrease of ε0 and Veff is attributed respectively to the pinning of acetamide molecules by ions and orientation jumps and undetected portion to the limited frequency coverage employed in these measurements

Direct Observation of Interfacial Dzyaloshinskii-Moriya Interaction from Asymmetric Spin-wave Propagation in W/CoFeB/SiO 2 Heterostructures Down to Sub-nanometer CoFeB Thickness

Interfacial Dzyaloshinskii-Moriya interaction (IDMI) is important for its roles in stabilizing the skyrmionic lattice as well as soliton-like domain wall motion leading towards new generation spintronic devices. However, achievement and detection of IDMI is often hindered by various spurious effects. Here, we demonstrate the occurrence of IDMI originating primarily from W/CoFeB interface in technologically important W/CoFeB/SiO2 heterostructures using Brillouin light scattering technique. Due to the presence of IDMI, we observe asymmetry in the peak frequency and linewidth of the spin-wave spectra in the Damon-Eshbach (DE) geometry at finite k wave-vectors. The DMI constant is found to scale as the inverse of CoFeB thickness, over the whole studied thickness range, confirming the presence of IDMI in our system without any extrinsic effects. Importantly, the W/CoFeB interface shows no degradation down to sub-nanometer CoFeB thickness, which would be useful for devices that aim to use pronounced interface effects.

All-optical detection of the spin Hall angle in W/CoFeB/SiO2 heterostructures with varying thickness of the tungsten layer

The development of advanced spintronics devices hinges on the efficient generation and utilization of pure spin current. In materials with large spin-orbit coupling, the spin Hall effect may convert charge current to pure spin current, and a large conversion efficiency, which is quantified by spin Hall angle (SHA), is desirable for the realization of miniaturized and energy-efficient spintronic devices. Here, we report a giant SHA in beta-tungsten (\ensuremath{\beta}-W) thin films in

Tunable configurational anisotropy in collective magnetization dynamics of Ni80Fe20 nanodot arrays with varying dot shapes

\mathrm{Sub}\text{/}\mathrm{W}(t)\text{/}\mathrm{C}{\mathrm{o}}_{20}\mathrm{F}{\mathrm{e}}_{60}{\mathrm{B}}_{20}(3\phantom{\rule{0.16em}{0ex}}\mathrm{nm})\text{/}\mathrm{Si}{\mathrm{O}}_{2}(2\phantom{\rule{0.16em}{0ex}}\mathrm{nm})

Shape- and Interface-Induced Control of Spin Dynamics of Two-Dimensional Bicomponent Magnonic Crystals

heterostructures with variable W thickness. We employed an all-optical time-resolved magneto-optical Kerr effect microscope for an unambiguous determination of SHA using the principle of modulation of Gilbert damping of the adjacent ferromagnetic layer by the spin-orbit torque from the W layer. A nonmonotonic variation of SHA with W layer thickness (

Efficient terahertz anti-reflection properties of metallic anti-dot structures

t

All optical detection of picosecond spin-wave dynamics in 2D annular antidot lattice

) is observed with a maximum of about 0.4 at about

Collective hydration dynamics in some amino acid solutions: A combined GHz-THz spectroscopic study

t=3\phantom{\rule{0.16em}{0ex}}\mathrm{nm}

Bias field tunable magnetic configuration and magnetization dynamics in Ni80Fe20 nano-cross structures with varying arm length

, followed by a sudden reduction to a very low value at

Efficient Modulation of Spin Waves in Two-Dimensional Octagonal Magnonic Crystal

t=6\phantom{\rule{0.16em}{0ex}}\mathrm{nm}