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Biswarup Satpati

Publications and source records attributed to Biswarup Satpati.

At least 37 records · Page 2Linked to original sources
arXiv2019

Tuning spinterface properties in Iron/Fullerene thin films

In ferromagnetic (FM) metal/organic semiconductor (OSC) heterostructures charge transfer can occur which leads to induction of magnetism in the non-magnetic OSC. This phenomenon has been described by the change in the density of states in the OSC which leads to a finite magnetic moment at the OSC interface and it is called the "spinterface". One of the main motivation in this field of organic spintronics is how to control the magnetic moment in the spinterface. In this regard, there are several open questions such as (i) which combination of FM and OSC can lead to more moment at the spinterface? (ii) Is the thickness of OSC also important? (iii) How does the spinterface moment vary with the FM thickness? (iv) Does the crystalline quality of the FM matters? (v) What is the effect of spinterface on magnetization reversal, domain structure and anisotropy? In this context, we have tried to answer the last three issues in this paper by studying Fe/C$_{60}$ bilayers of variable Fe thickness deposited on Si substrates. We find that both the induced moment and thickness of the spinterface vary proportionally with the Fe thickness. Such behavior is explained in terms of the growth quality of the Fe layer on the native oxide of the Si (100) substrate. The magnetization reversal, domain structure and anisotropy of these bilayer samples were studied and compared with their respective reference samples without having the C$_{60}$ layer. It is observed that the formation of spinterface leads to reduction in uniaxial anisotropy in Fe/C$_{60}$ on Si (100) in comparison to their reference samples.

physics.app-ph↗
arXiv2019

Effect of hydrostatic pressure on ferromagnetism in two-dimensional CrI$_3$

We have investigated the magnetic properties of highly anisotropic layered ferromagnetic semiconductor CrI$_3$ in presence of hydrostatic pressure ($P$). At ambient pressure, magnetization exhibits a clear anomaly below 212 K along with a thermal hysteresis over a wide temperature range (212-180 K), where a first-order structural transition is observed. CrI$_3$ undergoes a second-order ferromagnetic-paramagnetic phase transition with Curie temperature $T_C$=60.4 K. With application of pressure, the transition becomes sharper and $T_C$ is found to increase from 60.4 to 64.9 K as $P$ increases from 0 to 1.0 GPa. $T_C$ increases with $P$ in a sublinear fashion. The thermal hysteresis in magnetization and the increase of $T_C$ with pressure suggest that the spin and lattice degrees of freedom are coupled. The observed increase in $T_C$ has been explained on the basis of change in inter-layer coupling and Cr-I-Cr bond angle with pressure.

cond-mat.mtrl-sci↗
arXiv2019

Magnetotransport properties and giant anomalous Hall angle in half-Heusler compound TbPtBi

Magnetic lanthanide half-Heuslers ($R$PtBi; $R$ being the lanthanide) represent an attractive subgroup of the Heusler family and have been identified as ideal candidates for time reversal symmetry breaking topological Weyl semimetals. In this paper, we present the detailed analysis of the magnetotransport properties of frustrated antiferromagnet TbPtBi. This material shows large, non-saturating magnetoresistance (MR) with unusual magnetic field dependence. The MR of TbPtBi is significantly anisotropic with respect to the magnetic field, applied along different crystallographic directions and indicates the anisotropic nature of the Fermi surface. The chiral anomaly induced negative longitudinal magnetoresistance confirms the presence of Weyl fermions. At low temperature, Berry phase driven large anomalous Hall conductivity has been observed. The calculated anomalous Hall angle is the largest reported so far.

cond-mat.mtrl-sci↗
arXiv2018

Huge magnetoresistance and ultra-sharp metamagnetic transition in polycrystalline ${Sm_{0.5}Ca_{0.25}Sr_{0.25}MnO_3}$

Large magnetoresistive materials are of immense interest for a number of spintronic applications by developing high density magnetic memory devices, magnetic sensors and magnetic switches. Colossal magnetoresistance, for which resistivity changes several order of magnitude (${\sim10^4 \%}$) in an external magnetic field, occurs mainly in phase separated oxide materials, namely manganites, due to the phase competition between the ferromagnetic metallic and the antiferromagnetic insulating regions. Can one further enhance the magnetoresistance by tuning the volume fraction of the two phases? In this work, we report a huge colossal magnetoresistance along with the ultra-sharp metamagnetic transition in half doped ${Sm_{0.5}Ca_{0.25}Sr_{0.25}MnO_3}$ manganite compound by suitably tuning the volume fraction of the competing phases. The obtained magnetoresistance value at 10 K is as large as $\sim10^{13}\%$ in a 30 kOe external magnetic field and $\sim10^{15}\%$ in 90 kOe external magnetic field and is several orders of magnitude higher than any other observed magnetoresistance value reported so far. Using model Hamiltonian calculations we have shown that the inhomogeneous disorder, deduced from tunneling electron microscopy, suppresses the CE-type phase and seeds the ferromagnetic metal in an external magnetic field.

cond-mat.mtrl-sci↗
arXiv2018

Planar Hall effect in type II Dirac semimetal VAl$_{3}$

The study of electronic properties in topological systems is one of the most fascinating topics in condensed matter physics, which has generated enormous interests in recent times. New materials are frequently being proposed and investigated to identify their non-trivial band structure. While sophisticated techniques such as angle-resolved photoemission spectroscopy have become popular to map the energy-momentum relation, the transport experiments lack any direct confirmation of Dirac and Weyl fermions in a system. From band structure calculations, VAl$_{3}$ has been proposed to be a type II topological Dirac semimetal. This material represents a large family of isostructural compounds, all having similar electronic band structure and is an ideal system to explore the rich physics of Lorentz symmetry violating Dirac fermions. In this work, we present a detailed analysis on the magnetotransport properties of VAl$_{3}$. A large, non-saturating magnetoresistance has been observed. Hall resistivity reveals the presence of two types of charge carriers with high mobility. Our measurements show a large planar Hall effect in this material, which is robust and can be easily detectable up to high temperature. This phenomenon originates from the relativistic chiral anomaly and non-trivial Berry curvature, which validates the theoretical prediction of the Dirac semimetal phase in VAl$_{3}$.

cond-mat.mtrl-sci↗
arXiv2018

Magneto-transport properties of proposed triply degenerate topological semimetal Pd$_{3}$Bi$_{2}$S$_{2}$

We report transport properties of single-crystalline Pd$_{3}$Bi$_{2}$S$_{2}$, which has been predicted to host an unconventional electronic phase of matter beyond three-dimensional Dirac and Weyl semimetals. Similar to several topological systems, the resistivity shows field induced metal-semiconductor-like crossover at low temperature. Large, anisotropic and non-saturating magnetoresistance (MR) has been observed in transverse experimental configuration. At 2 K and 9 T, the MR value reaches as high as $\sim$1.1$\times$10$^{3}$ \%. Hall resistivity reveals the presence of two types of charge carriers and has been analyzed using two-band model. In spite of the large density ($>$ 10$^{21}$ cm$^{-3}$), the mobility of charge carriers is found to be quite high ($\sim$ 0.75$\times$10$^{4}$ cm$^{2}$ V$^{-1}$ s$^{-1}$ for hole and $\sim$ 0.3$\times$10$^{4}$ cm$^{2}$ V$^{-1}$ s$^{-1}$ for electron). The observed magneto-electrical properties indicate that Pd$_{3}$Bi$_{2}$S$_{2}$ may be a new member of the topological semimetal family, which can have a significant impact in technological applications.

cond-mat.mtrl-sci↗
arXiv2018

Probing lattice dynamics and electron-phonon coupling in topological nodal-line semimetal ZrSiS

Topological materials provide an exclusive platform to study the dynamics of relativistic particles in table-top experiments and offer the possibility of wide-scale technological applications. ZrSiS is a newly discovered topological nodal-line semimetal and has drawn enormous interests. In this report, we have investigated the lattice dynamics and electron-phonon interaction in single crystalline ZrSiS using Raman spectroscopy. Polarization and angle resolved measurements have been performed and the results have been analyzed using crystal symmetries and theoretically calculated atomic vibrational patterns along with phonon dispersion spectra. Wavelength and temperature dependent measurements show the complex interplay of electron and phonon degrees of freedom, resulting in resonant phonon and quasielastic electron scatterings through inter-band transitions. Our high-pressure Raman studies reveal vibrational anomalies, which were further investigated from the high-pressure synchrotron x-ray diffraction (HPXRD) spectra. From HPXRD, we have clearly identified pressure-induced structural transitions and coexistence of multiple phases, which also indicate possible electronic topological transitions in ZrSiS. The present study not only provides the fundamental information on the phonon subsystem, but also sheds some light in understanding the topological nodal-line phase in ZrSiS and other iso-structural systems.

cond-mat.mtrl-sci↗
arXiv2018

Magnetotransport properties and evidence of topological insulating state in LaSbTe

In this report, we present the magnetotransport and magnetization properties of LaSbTe single crystals. Magnetic field-induced turn-on behavior and low-temperature resistivity plateau have been observed. By adopting both metal-semiconductor crossover and Kohler scaling analysis, we have discussed the possible origin of the temperature and magnetic field dependence of resistivity. At 5 K and 9 T, a large, non-saturating transverse magnetoresistance (MR) $\sim$ 5$\times$10$^{3}$ \% has been obtained. The MR shows considerable anisotropy, when the magnetic field is applied along different crystallographic directions. The non-linear field dependence of the Hall resistivity confirms the presence of two types of charge carriers. From the semiclassical two-band fitting of Hall conductivity and longitudinal conductivity, very high carrier mobilities and almost equal electron and hole densities have been deduced, which result in large MR. The Fermi surface properties have been analyzed from de Haas-van Alphen oscillation. From the magnetization measurement, the signature of non-trivial surface state has been detected, which confirms that LaSbTe is a topological insulator, consistent with the earlier first-principles calculations.

cond-mat.mtrl-sci↗
arXiv2017

Anisotropic Fermi surface probed by the de Haas-van Alphen oscillation in proposed Dirac Semimetal TaSb$_{2}$

TaSb$_{2}$ has been predicted theoretically and proposed through magnetotransport experiment to be a topological semimetal. In earlier reports, the Shubnikov-de Haas oscillation has been analyzed to probe the Fermi surface, with magnetic field along a particular crystallographic axis only. By employing a sample rotator, we reveal highly anisotropic transverse magnetoresistance by rotating the magnetic field along different crystallographic directions. To probe the anisotropy in the Fermi surface, we have performed magnetization measurements and detected strong de Haas-van Alphen (dHvA) oscillations for the magnetic field applied along \textbf{b} and \textbf{c} axes as well as perpendicular to \textbf{bc} plane of the crystals. Three Fermi pockets have been identified by analyzing the dHvA oscillations. Hall measurement reveals electron as the only charge carrier, i.e., all the three Fermi pockets are electron type. With the application of magnetic field along different crystal directions, the cross sectional areas of the Fermi pockets have been found significantly different. Other physical parameters, such as the effective mass of the charge carrier and Fermi velocity have also been calculated using the Lifshitz-Kosevich formula.

cond-mat.mtrl-sci↗
arXiv2017

Fermi surface topology and signature of surface Dirac nodes in LaBi

Novel topological state of matter is one of the rapidly growing fields in condensed matter physics research in recent times. While these materials are fascinating from the aspect of fundamental physics of relativistic particles, their exotic transport properties are equally compelling due to the potential technological applications. Extreme magnetoresistance and ultrahigh carrier mobility are two such major hallmarks of topological materials and often used as primary criteria for identifying new compounds belonging to this class. Recently, LaBi has emerged as a new system, which exhibits the above mentioned properties. However, the topological nature of its band structure remains unresolved. Here, using the magnetotransport and magnetization measurements, we have probed the bulk and surface states of LaBi. Similar to earlier reports, extremely large magnetoresistance and high carrier mobility have been observed with compensated electron and hole density. The Fermi surface properties have been analyzed from both Shubnikov-de Haas and de Haas-van Alphen oscillation techniques. In the magnetization measurement, a prominent paramagnetic singularity has been observed, which demonstrates the non-trivial nature of the surface states in LaBi. Our study unambiguously confirms that LaBi is a three-dimensional topological insulator with possible linear dispersion in the gapped bulk band structure.

cond-mat.mtrl-sci↗
arXiv2017

Probing Localized Surface Plasmons of Trisoctahedral Gold Nanocrystals for Surface Enhanced Raman Scattering

Trisoctahedral (TOH) shaped Au nanocrystals (NCs) have emerged as a new class of metal nanoparticles (MNP) due to its superior catalystic and SERS activities caused by the presence of high density atomic steps and dangling bonds on their high index facets. We examine the radiative localized surface plasmon resonance (LSPR) modes of an isolated single TOH Au NC using cathodoluminescence (CL), with high resolution spatial information of the local density of optical states (LDOS) across the visible spectral range. Further we show pronounced enhancement factor in the Raman scattering by performing Raman spectroscopic measurements on Rhodamine 6G (R6G) covered TOH Au NPs aggregates on a Si substrate. We believe that the hot spots between two adjacent MNP surfaces (nanogaps) can be significantly stronger than single particle LSPRs. Such nanogaps hotspots may have crucial role on the substantial SERS enhancement observed in this report. Consequently, the present study indicates that MNPs aggregates are highly desirable than individual plasmonic nanoparticles for possible applications in SERS based biosensing.

cond-mat.mtrl-sci↗
arXiv2016

Nanoscale η-NiSi formation via ion irradiation of Si/Ni/Si

Nickel monosilicide (NiSi) has emerged as an excellent material of choice for source-drain contact applications below 45 nm node complementary metal-oxide-semiconductor (CMOS) technology. We have investigated the formation of nanoscale NiSi by ion irradiation of Si (~5 nm)/Ni(~15 nm)/Si, grown under ultrahigh vacuum environment. Irradiation was carried out at room temperature with 1 MeV Si+ ions. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were employed for analysis. With increasing ion fluence ion beam mixing occurs and more and more Si is incorporated into the Ni layer and this layer gets amorphized. At an even higher fluence a recrystallized uniform nickel monosilicide (η-NiSi) layer is formed. Several planar spacings of different Miller indices of η-NiSi have been observed in XRD and TEM. Additionally, an oscillatory amorphization and recrystallization has been observed in the substrate Si with increasing ion fluence. To our knowledge, this has never been observed in ion irradiation of bare Si in decades of work in this area. The oscillatory amorphization/recrystallization in Si is apparently Ni-induced. Irradiation displaces Ni and produces a distribution of Ni in amorphized Si. Irradiation at a higher fluence produces two recrystallized Si bands in amorphous Si with concomitant accumulation of Ni at the amorphous/crystalline interfaces. On further increase of irradiation fluence the recrystallized Si bands again pass through amorphization and recrystallization. The total thickness of recrystallized as well as amorphous Si shows an oscillatory behavior as a function of ion fluence.

cond-mat.mtrl-sci↗
arXiv2016

Temperature and high fluence induced ripple rotation on Si(100) surface

Topography evolution of Si(100) surface due to oblique incidence low energy ion beam sputtering (IBS) is investigated. Experiments were carried out at different elevated temperatures from 20$^{\circ}$C to 450$^{\circ}$C and at each temperature, the ion fluence is systematically varied in a wide range from $\sim$ 1$\times$10$^{18}$cm$^{-2}$ to 1$\times$10$^{20}$cm$^{-2}$. The ion sputtered surface morphologies are characterized by atomic force microscopy and high-resolution cross-sectional transmission electron microscopy. At room temperature, the ion sputtered surfaces show periodic ripple nanopatterns and their wave-vector remains parallel to ion beam projection for entire fluence range. With increase of substrate temperature, these patterns tend to demolish and reduce into randomly ordered mound-like structures around 350$^{\circ}$C. Further rise in temperature above 400$^{\circ}$C leads, surprisingly, orthogonally rotated ripples beyond fluence 5$\times$10$^{19}$cm$^{-2}$. All the results are discussed combining the theoretical framework of linear, non-linear and recently developed mass redistribution continuum models of pattern formation by IBS. These results have technological importance regarding the control over ion induced pattern formation as well as it provides useful information for further progress in theoretical field.

cond-mat.mtrl-sci↗
arXiv2016

Structural and Electrical Properties of MoTe$_2$ and MoSe$_2$ Grown by Molecular Beam Epitaxy

We demonstrate the growth of thin films of molybdenum ditelluride and molybdenum diselenide on sapphire substrates by molecular beam epitaxy. In-situ structural and chemical analyses reveal stoichiometric layered film growth with atomically smooth surface morphologies. Film growth along the (001) direction is confirmed by X-ray diffraction, and the crystalline nature of growth in the 2H phase is evident from Raman spectroscopy. Transmission electron microscopy is used to confirm the layered film structure and hexagonal arrangement of surface atoms. Temperature dependent electrical measurements show an insulating behavior which agrees well with a two-dimensional variable-range hopping model, suggesting that transport in these films is dominated by localized charge-carrier states.

cond-mat.mtrl-sci↗
arXiv2015

Inducing magnetism onto the surface of a topological crystalline insulator

Inducing magnetism onto a topological crystalline insulator (TCI) has been predicted to result in several novel quantum electromagnetic effects. This is a consequence of the highly strain-sensitive band topology of such symmetry-protected systems. We thus show that placing the TCI surface of SnTe in proximity to EuS, a ferromagnetic insulator, induces magnetism at the interface between SnTe and EuS and thus breaks time-reversal-symmetry in the TCI. Magnetotransport experiments on SnTe-EuS-SnTe trilayer devices reveal a hysteretic lowering of the resistance at the TCI surface that coincides with an increase in the density of magnetic domain walls. This additional conduction could be a signature of topologically-protected surface states within domain walls. Additionally, a hysteretic anomalous Hall effect reveals that the usual in-plane magnetic moment of the EuS layer is canted towards a perpendicular direction at the interface. These results are evidence of induced magnetism at the SnTe-EuS interfaces resulting in broken time-reversal symmetry in the TCI.

cond-mat.mes-hall↗
arXiv2014

Quantum Coherent Transport in SnTe Topological Crystalline Insulator Thin Films

Topological crystalline insulators (TCI) are unique systems where a band inversion that is protected by crystalline mirror symmetry leads to a multiplicity of topological surface states. Binary SnTe is an attractive lead-free TCI compound; the present work on high-quality thin films provides a route for increasing the mobility and reducing the carrier density of SnTe without chemical doping. Results of quantum coherent magnetotransport measurements reveal a multiplicity of Dirac surface states that are unique to TCI. Modeling of the weak antilocalization shows variations in the extracted number of carrier valleys that reflect the role of coherent intervalley scattering in coupling different Dirac states on the degenerate TCI surface.

cond-mat.mes-hall↗
arXiv2013

Large area buried nanopatterning by broad ion implantation without any mask or direct writing

We have introduced here a simple, single step and cost effective broad ion beam technique for preparation of nanoscale electronic, magnetic, optical and mechanical devices without the need of resist, mask, or focused electron and ion beams. In this approach, broad beam ion implantation of desired atom on a prefabricated ion beam patterned surface promotes site selective deposition by adjusting the local angle of ion implantation. We show that implantation of Fe ions on an O+ induced pre fabricated triangular shaped patterned Si surface results in a self-organized periodic array of striped magnetic nanostructures having several micron length and about 50 nm width arranged with a lateral separation of ~ 200 nm. The morphology, composition, crystalline structure and magnetic property of these nanopatterns have been analyzed and the crucial feature of such nanopattern formation by broad beam ion implantation is explained.

cond-mat.mes-hall↗