arXiv subjects

V. Nagarajan

Publications and source records attributed to V. Nagarajan.

At least 19 recordsLinked to original sources

arXiv2023

Strain Dependent Spin Hall Magnetoresistance in the Multiferroic Antiferromagnet BiFeO$_3$

The spin Hall magnetoresistance (SMR) of epitaxial BiFeO$_3$ thin films is investigated. SMR consistent with ferromagnetic interfacial states for BiFeO$_3$ films fabricated on (001) SrTiO$_3$ (R' BFO) and LaAlO$_3$ (T' BFO) substrates is found, albeit with different temperature dependencies. For T' BFO, the SMR is enhanced at room temperature, and decays with reduced temperatures. By contrast, R' BFO shows a monotonic decrease in SMR response with increasing temperature, mirroring the trend of a weak ferromagnet. Density functional theory shows that this difference originates from the coupling of the applied magnetic field to oxygen octahedral rotation (R') and spin (T') degrees of freedom.

cond-mat.mtrl-sci↗

arXiv2022

Ferroelectric Solitons Crafted in Epitaxial Bismuth Ferrite Superlattices

In ferroelectrics, complex interactions among various degrees of freedom enable the condensation of topologically protected polarization textures. Known as ferroelectric solitons, these particle-like structures represent a new class of materials with promise for beyond CMOS technologies due to their ultrafine size and sensitivity to external stimuli. Such polarization textures have scarcely been reported in multiferroics. Here, we report a range of soliton topologies in bismuth ferrite strontium titanate superlattices. High-resolution piezoresponse force microscopy and Cs-corrected high-angle annular dark-field scanning transmission electron microscopy reveal a zoo of topologies, and polarization displacement mapping of planar specimens reveals center-convergent and divergent topological defects as small as 3 nm. Phase field simulations verify that some of these topologies can be classed as bimerons, with a topological charge of plus and minus one, and first-principles-based effective Hamiltonian computations show that the co-existence of such structures can lead to non-integer topological charges, a first observation in a BiFeO3-based system. Our results open new opportunities in multiferroic topotronics.

cond-mat.mtrl-sci↗

arXiv2020

Detection of odor quality and ripening stage of Mangifera indica L. by graphdiyne nanosheet -- a DFT outlook

Using first-principles calculation, geometrical stability together with electronic properties of graphdiyne nanosheet (Gdn-NS) is investigated. The structural stability of Gdn-NS is established with the support of phonon band structure and cohesive energy. The main objective of the present study is to check the odor quality of Mangifera indica L. (mangoes) fruits during the various ripening stage with the influence of Gdn-NS material. In addition, the adsorption of various volatiles, namely ethyl butanoate, myrcene, (E,Z,Z)-1,3,4,8-undecatetraene and $γ$-octalactone aromas on Gdn-NS is explored with the significant parameters including Bader charge transfer, energy gap, average energy gap changes and adsorption energy. The sensitivity of volatiles emitting from various ripening stages of mango on Gdn-NS were explored with the influence of density of states spectrum. The outcomes of the proposed work help us to check the ripening stage and odor quality of Mangifera indica L. by Gdn-NS material using density functional theory.

cond-mat.mtrl-sci↗

arXiv2020

Hermes: a Fast, Fault-Tolerant and Linearizable Replication Protocol

Today's datacenter applications are underpinned by datastores that are responsible for providing availability, consistency, and performance. For high availability in the presence of failures, these datastores replicate data across several nodes. This is accomplished with the help of a reliable replication protocol that is responsible for maintaining the replicas strongly-consistent even when faults occur. Strong consistency is preferred to weaker consistency models that cannot guarantee an intuitive behavior for the clients. Furthermore, to accommodate high demand at real-time latencies, datastores must deliver high throughput and low latency. This work introduces Hermes, a broadcast-based reliable replication protocol for in-memory datastores that provides both high throughput and low latency by enabling local reads and fully-concurrent fast writes at all replicas. Hermes couples logical timestamps with cache-coherence-inspired invalidations to guarantee linearizability, avoid write serialization at a centralized ordering point, resolve write conflicts locally at each replica (hence ensuring that writes never abort) and provide fault-tolerance via replayable writes. Our implementation of Hermes over an RDMA-enabled reliable datastore with five replicas shows that Hermes consistently achieves higher throughput than state-of-the-art RDMA-based reliable protocols (ZAB and CRAQ) across all write ratios while also significantly reducing tail latency. At 5% writes, the tail latency of Hermes is 3.6X lower than that of CRAQ and ZAB.

cs.DC↗

arXiv2019

Silicene nanosheet to discriminate the quality of pear fruit based on volatiles adsorption --- a DFT application

We report the interaction between the silicene nanosheet (Si-NS) and volatile organic compounds (VOCs) released from the pear fruit (Pyrus communis) in ripened and over-ripened stages using density functional theory (DFT) technique. The geometric stability of Si-NS is studied from the phonon band structure. Further, the electronic property of Si-NS is studied from the energy band gap structure, and the energy gap is found to be 0.46 eV, which exhibits semiconductor property. The outcomes infer that the adsorption of volatiles released from the pear fruit on silicene nanosheet is in the following order hexyl acetate $\rightarrow$ butyl acetate $\rightarrow$ butyl butyrate in the ripened stage whereas in the over-ripened stage the adsorption sequence is noticed to be acetic acid $\rightarrow$ ethyl acetate $\rightarrow$ 1-butanol. The adsorption property of pear fruit volatiles on silicene nanosheet is documented with the adsorption energy, average energy gap changes, and Bader charge transfer. Moreover, the adsorption of VOCs on silicene nanosheet is also explored using the energy band structure, electron density along with the adsorption sites and density of states (DOS) spectrum. Besides, the findings reveal that the silicene nanosheet can be used to discriminate the quality of pear fruit.

cond-mat.mes-hall↗

arXiv2019

Nitrogen dioxide and ammonia gas molecules interaction studies on phosphorene nanosheet --- a DFT investigation

The adsorption behaviour of hazardous gas molecules, namely nitrogen dioxide (NO$_2$) and ammonia (NH$_3$), on phosphorene nanosheet (PNS) was explored by means of ab initio technique. To improve the structural solidity of pristine PNS, we have introduced the passivation of hydrogen and fluorine at the terminated edge. The structural solidity of both hydrogen and fluorine passivated PNS is verified in terms of formation energy. The main objective of this research work is to probe NO$_2$ and NH$_3$ gases using PNS as a base sensing material. The adsorption of various preferential adsorption sites of these gas molecules is studied in accordance with the average HOMO-LUMO gap changes, natural-bond-orbital (NBO) charge transfer, HOMO-LUMO gap, and adsorption energy. Notably, the negative value of adsorption energy is found upon the adsorption of NO$_2$ and NH$_3$ on PNS and it is in the range of $-1.36$ to $-2.45$ eV. The findings of the present research work recommend that the hydrogenated and fluorinated PNS can be effectively used as a chemical sensor against NO$_2$ and NH$_3$ molecules.

cond-mat.mes-hall↗

arXiv2019

Coexistence of orbital and quantum critical magnetoresistance in FeSe$_{1-x}$S$_{x}$

The recent discovery of a non-magnetic nematic quantum critical point (QCP) in the iron chalcogenide family FeSe$_{1-x}$S$_{x}$ has raised the prospect of investigating, in isolation, the role of nematicity on the electronic properties of correlated metals. Here we report a detailed study of the normal state transverse magnetoresistance (MR) in FeSe$_{1-x}$S$_{x}$ for a series of S concentrations spanning the nematic QCP. For all temperatures and \textit{x}-values studied, the MR can be decomposed into two distinct components: one that varies quadratically in magnetic field strength $μ_{0}\textit{H}$ and one that follows precisely the quadrature scaling form recently reported in metals at or close to a QCP and characterized by a \textit{H}-linear MR over an extended field range. The two components evolve systematically with both temperature and S-substitution in a manner that is determined by their proximity to the nematic QCP. This study thus reveals unambiguously the coexistence of two independent charge sectors in a quantum critical system. Moreover, the quantum critical component of the MR is found to be less sensitive to disorder than the quadratic (orbital) MR, suggesting that detection of the latter in previous MR studies of metals near a QCP may have been obscured.

cond-mat.str-el↗

arXiv2018

Switching behaviour of stilbene molecular device: a first-principles study

The switching behaviour of stilbene molecular system (SMS) device is investigated with the help of non-equilibrium Green's function (NEGF) approach using first principles calculation. The transmission spectrum of cis-isomers confirmed that more electrons are transferred across the SMS-device using optical excitation by the spin of C$=$C bond by torsion angle $(θ=180^\circ)$. The current-voltage characteristics show the lower magnitude of current for trans-stilbene and higher magnitude of current for cis-stilbene for an externally applied bias voltage. The outcome of the proposed work suggests that cis and trans-stilbene molecular device can be used as a switch.

cond-mat.mes-hall↗

arXiv2017

Sensing behavior of acetone vapors on TiO$_2$ nanostructures --- application of density functional theory

The electronic properties of TiO$_2$ nanostructure are explored using density functional theory. The adsorption properties of acetone on TiO$_2$ nanostructure are studied in terms of adsorption energy, average energy gap variation and Mulliken charge transfer. The density of states spectrum and the band structure clearly reveals the adsorption of acetone on TiO$_2$ nanostructures. The variation in the energy gap and changes in the density of charge are observed upon adsorption of acetone on n-type TiO$_2$ base material. The results of DOS spectrum reveal that the transfer of electrons takes place between acetone vapor and TiO$_2$ base material. The findings show that the adsorption property of acetone is more favorable on TiO$_2$ nanostructure. Suitable adsorption sites of acetone on TiO$_2$ nanostructure are identified at atomistic level. From the results, it is confirmed that TiO$_2$ nanostructure can be efficiently utilized as a sensing element for the detection of acetone vapor in a mixed environment.

cond-mat.mes-hall↗

arXiv2017

Investigation on nickel ferrite nanowire device exhibiting negative differential resistance $-$ a first-principles investigation

The electronic property of NiFe$_2$O$_4$ nanowire device is investigated through nonequilibrium Green's functions (NEGF) in combination with density functional theory (DFT). The electronic transport properties of NiFe$_2$O$_4$ nanowire are studied in terms of density of states, transmission spectrum and $I{-}V$ characteristics. The density of states gets modified with the applied bias voltage across NiFe$_2$O$_4$ nanowire device, the density of charge is observed both in the valence band and in the conduction band on increasing the bias voltage. The transmission spectrum of NiFe$_2$O$_4$ nanowire device gives the insights on the transition of electrons at different energy intervals. The findings of the present work suggest that NiFe$_2$O$_4$ nanowire device can be used as negative differential resistance (NDR) device and its NDR property can be tuned with the bias voltage, which may be used in microwave device, memory devices and in fast switching devices.

cond-mat.mes-hall↗

arXiv2017

Interaction of NH$_3$ gas on $α$-MoO$_3$ nanostructures $-$ a DFT investigation

The structural stability, electronic properties and NH$_3$ adsorption properties of pristine, Ti, Zr and F substituted $α$-MoO$_3$ nanostructures are successfully studied using density functional theory with B3LYP/LanL2DZ basis set. The structural stability of $α$-MoO$_3$ nanostructures is discussed in terms of formation energy. The electronic properties of pristine, Ti, Zr and F incorporated $α$-MoO$_3$ nanostructures are discussed in terms of HOMO-LUMO gap, ionization potential and electron affinity. $α$-MoO$_3$ nanostructures can be fine-tuned with suitable substitution impurity to improve the adsorption characteristics of ammonia, which can be used to detect NH$_3$ in a mixed environment. The present work gives an insight into tailoring $α$-MoO$_3$ nanostructures for NH$_3$ detection.

cond-mat.mes-hall↗

arXiv2015

Strain-induced magnetic phase transition in SrCoO$_{3-δ}$ thin films

It has been well established that both in bulk at ambient pressure and for films under modest strains, cubic SrCoO$_{3-δ}$ ($δ< 0.2$) is a ferromagnetic metal. Recent theoretical work, however, indicates that a magnetic phase transition to an antiferromagnetic structure could occur under large strain accompanied by a metal-insulator transition. We have observed a strain-induced ferromagnetic to antiferromagnetic phase transition in SrCoO$_{3-δ}$ films grown on DyScO$_3$ substrates, which provide a large tensile epitaxial strain, as compared to ferromagnetic films under lower tensile strain on SrTiO$_3$ substrates. Magnetometry results demonstrate the existence of antiferromagnetic spin correlations and neutron diffraction experiments provide a direct evidence for a G-type antiferromagnetic structure with Neél temperatures between $T_N \sim 135\,\pm\,10\,K$ and $\sim 325\,\pm\,10\,K$ depending on the oxygen content of the samples. Therefore, our data experimentally confirm the predicted strain-induced magnetic phase transition to an antiferromagnetic state for SrCoO$_{3-δ}$ thin films under large epitaxial strain.

cond-mat.mtrl-sci↗

arXiv2014

Element-Specific Depth Profile of Magnetism and Stoichiometry at the La0.67Sr0.33MnO3/BiFeO3 Interface

Depth-sensitive magnetic, structural and chemical characterization is important in the understanding and optimization of novel physical phenomena emerging at interfaces of transition metal oxide heterostructures. In a simultaneous approach we have used polarized neutron and resonant X-ray reflectometry to determine the magnetic profile across atomically sharp interfaces of ferromagnetic La0.67Sr0.33MnO3 / multiferroic BiFeO3 bi-layers with sub-nanometer resolution. In particular, the X-ray resonant magnetic reflectivity measurements at the Fe and Mn resonance edges allowed us to determine the element specific depth profile of the ferromagnetic moments in both the La0.67Sr0.33MnO3 and BiFeO3 layers. Our measurements indicate a magnetically diluted interface layer within the La0.67Sr0.33MnO3 layer, in contrast to previous observations on inversely deposited layers. Additional resonant X-ray reflection measurements indicate a region of an altered Mn- and O-content at the interface, with a thickness matching that of the magnetic diluted layer, as origin of the reduction of the magnetic moment.

cond-mat.str-el↗

arXiv2010

Probing La(0.7)Sr(0.3)MnO3 multilayers via spin wave resonances

La(0.7)Sr(0.3)MnO3/BiFeO3 and La(0.7)Sr(0.3)MnO3/PbZr20Ti80O3 epitaxial heterostructures have been grown on SrTiO3 substrates. Spin wave resonances are used to study interface properties of the ferromagnetic La(0.7)Sr(0.3)MnO3. We find that the addition of the BiFeO3 or PbZr20Ti80O3 causes out-of-plane surface pinning of the La(0.7)Sr(0.3)MnO3. We are able to place new limits on the exchange constant D of La(0.7)Sr(0.3)MnO3 grown on these substrates and confirm the presence of uniaxial and biaxial anisotropies caused by the SrTiO3 substrate.

cond-mat.mtrl-sci↗

arXiv2010

Phase Coexistence Near a Morphotropic Phase Boundary in Sm-doped BiFeO3 Films

We have investigated heteroepitaxial films of Sm-doped BiFeO3 with a Sm-concentration near a morphotropic phase boundary. Our high-resolution synchrotron X-ray diffraction, carried out in a temperature range of 25C to 700C, reveals substantial phase coexistence as one changes temperature to crossover from a low-temperature PbZrO3-like phase to a high-temperature orthorhombic phase. We also examine changes due to strain for films greater or less than the critical thickness for misfit dislocation formation. Particularly, we note that thicker films exhibit a substantial volume collapse associated with the structural transition that is suppressed in strained thin films.

cond-mat.mtrl-sci↗

arXiv2010

Analysis of Birth weight using Singular Value Decomposition

The researchers have drawn much attention about the birth weight of newborn babies in the last three decades. The birth weight is one of the vital roles in the babys health. So many researchers such as (2),(1) and (4) analyzed the birth weight of babies. The aim of this paper is to analyze the birth weight and some other birth weight related variable, using singular value decomposition and multiple linear regression.

physics.data-an↗

arXiv2008

Complex phase mixture and domain superstructure across a new lead-free ferroelectric/anti-ferroelectric morphotropic phase boundary

We investigate the microstructural evolution in a ferroelectric to antiferroelectric phase transition at the morphotropic phase boundary in the Bi(1-x)SmxFeO3 system. Continuous Sm3+ substitution on the A-site induces short-range anti-parallel cation displacements as verified by the appearance of localized 1/4(110) weak spots in selected area electron diffraction patterns for 0.1<x<0.14 samples, and thus onset of antiferroelectricity. Kinetic Monte Carlo simulations confirm that increasing the strength of the anti-parallel interactions (i.e. increasing x) induces a ferroelectric to antiferroelectric transition. For 0.14<x<0.2 antiphase oxygen octahedra tilts induce complete antiferroelectricity.

cond-mat.mtrl-sci↗

arXiv2008

Combinatorial discovery of a lead-free morphotropic phase boundary in a thin-film piezoelectric perovskite

We report on the discovery of a lead-free morphotropic phase boundary in Sm doped BiFeO3 with a simple perovskite structure using the combinatorial thin film strategy. The boundary is a rhombohedral to pseudo-orthorhombic structural transition which exhibits a ferroelectric (FE) to antiferroelectric (AFE) transition at approximately Bi0.86Sm0.14FeO3 with dielectric constant and out-of-plane piezoelectric coefficient comparable to those of epitaxial (001) oriented Pb(Zr,Ti)O3 (PZT) thin films at the MPB. The discovered composition may be a strong candidate of a Pb-free piezoelectric replacement of PZT.

cond-mat.mtrl-sci↗