arXiv subjects

C. V. Tomy

Publications and source records attributed to C. V. Tomy.

At least 19 recordsLinked to original sources

arXiv2021

Direction dependent thermoelectric properties of layered compound In2Te5 single crystal

We analyze the anisotropic electrical and thermal transport measurements in single crystals of In2Te5 belonging to monoclinic space group C12 c1 with the temperature gradient applied parallel and perpendicular to the crystallographic c-axis of the crystals. The thermal conductivity along the c-axis thermal conductivity parallel was found to smaller by a factor of 2 compared to the thermal conductivity along the direction perpendicular to the c-axis over the entire temperature range. In contrast, the Seebeck coefficient along the c-axis parallel was found to be higher than its value along the direction perpendicular to the c-axis. At room temperature, the figure of merit ZT parallel is found to be 4 times larger as compared to the figure of merit ZT perpendicular.

cond-mat.mtrl-sci↗

arXiv2020

A simple synthesis method for growing single crystals of a copper coordination polymer [Cu(C2O4)(4-aminopyridine)2(H2O)]n, and its theoretical and physical properties studies

This work reports on a novel and simple synthetic route for the growth of metal-organic crystal [Cu(C2O4)(4-aminopyridine)2(H2O)]n of large size using the technique of liquid-liquid diffusion or layer diffusion. Single crystal X-ray diffraction measurements revealed a very good quality of the grown single crystals with a small value 1.101 of goodness of fit R. Rietveld refinement done on powder X-ray diffractogram obtained on few single crystals crushed together revealed a very small value of R as 3.45, indicating very good crystal quality in a batch of crystals. Density functional theory with three different basis sets generated the optimized geometry of a monomeric unit as well as its vibrational spectra. Comparison between experimentally obtained bond lengths, bond angles, IR frequencies etc. suggest (B3LYP/LanL2DZ, B3LYP/6-311++ G(d,p) basis set to describe the properties the best. Magnetic susceptibility measurements confirm the metal-organic crystal [Cu(C2O4)(4-aminopyridine)2(H2O)]n to be a very good representation of a spin 1/2 Heisenberg antiferromagnet.

cond-mat.mtrl-sci↗

arXiv2020

Experimental realisation of multipartite entanglement via quantum Fisher information in a uniform antiferromagnetic quantum spin chain

Quantum entanglement is a quantum mechanical phenomenon where the quantum state of a many-body system with many degrees of freedom cannot be described independently of the state of each body with a given degree of freedom, no matter how far apart in space each body is. Entanglement is not only considered a resource in quantum information but also believed to affect complex condensed matter systems. Detecting and quantifying multi-particle entanglement in a many-body system is thus of fundamental significance for both quantum information science and condensed matter physics. Here, we detect and quantify multipartite entanglement in a spin 1/2 Heisenberg antiferromagnetic chain in a bulk solid. Multipartite entanglement was detected using quantum Fisher information which was obtained using dynamic susceptibility measured via inelastic neutron scattering. The scaling behaviour of quantum Fisher information was found to identify the spin 1/2 Heisenberg antiferromagnetic chain to belong to a class of strongly entangled quantum phase transitions with divergent multipartite entanglement.

quant-ph↗

arXiv2019

Investigation of the phase separation property in La$_{0.2}$Pr$_{0.4}$Ca$_{0.4}$MnO$_3$ manganite

We report a comprehensive investigation of La0.2Pr0.4Ca0.4MnO3 to clarify the micrometre scale phase separation phenomenon in the mixed valent manganite (La,Pr,Ca)MnO3. The compound shows multiple magnetic transitions, in which the charge-ordered state is converted into a ferromagnetic state in steps with the application of a magnetic field. The ac susceptibility measurements show that the glassy transition at low temperatures does not depend on the frequency, thus indicating the absence of any spin glass behaviour. Magnetization as well as heat capacity measurements indicate that this low temperature transition is magnetic field dependent. The field dependent resistivity at 2K shows a sharp drop indicating that the sample behaviour changes from a high resistive state to a low resistive state, corroborating the conversion of charge-ordered insulating (COI) phase to a ferromagnetic metallic (FMM) phase. Our results point towards the existence of phase separation, rigidity of the low temperature glassy-like phase as well as the conversion of COI phase to FMM phase by the application of magnetic fields.

cond-mat.mtrl-sci↗

arXiv2019

Muon spin rotation and neutron scattering investigations of the B-site ordered double perovskite Sr2DyRuO6

The magnetic ground state of double perovskite Sr2DyRuO6 has been investigated using muon spin rotation and relaxation (muSR), neutron powder diffraction (NPD) and inelastic neutron scattering (INS), in addition to heat capacity and magnetic susceptibility (ac and dc) measurements. A clear signature of a long-range ordered magnetic ground state has been observed in the heat capacity data, which exhibit two sharp anomalies at 39.5 and 36 K found as well in the magnetic data. Further confirmation of long-range magnetic ordering comes from a sharp drop in the muon initial asymmetry and a peak in the relaxation rate at 40 K, along with a weak anomaly near 36 K. Based on temperature dependent NPD, the low temperature magnetic structure contains two interpenetrating lattices of Dy and Ru5, forming an antiferromagnetic ground state below 39.5 K with magnetic propagation vector k = (0,0,0). The magnetic moments of Dy and Ru at 3.5 K are pointing along the crystallographic b-axis with values of muDy = 4.92(10) muB and muRu = 1.94(7) muB, respectively. The temperature dependence of the Ru moments follows a mean field type behaviour, while that of the Dy moments exhibits a deviation indicating that the primary magnetic ordering is induced by the order of the 4d electrons of Ru rather than that of its proper 4f Dy electrons. The origin of the second anomaly observed in the heat capacity data at 36.5 K must be connected to a very small spin reorientation as the NPD studies do not reveal any clear change in the observed magnetic Bragg peaks positions or intensities between these two transitions. INS measurements reveal the presence of crystal field excitations (CEF) in the paramagnetic state with overall CEF splitting of 73.8 meV, in agreement with the point change model calculations.

cond-mat.str-el↗

arXiv2018

Effect of B-site bismuth doping on magnetic and transport properties of La0.5Ca0.5Mn1-xBixO3 thin films

The magnetic properties in manganite have been found to be highly sensitive to the doping and structural manipulations. Here, we report the effect of B-site bismuth doping on the magnetic and transport properties in La0.5Ca0.5Mn1-xBixO3 (LCMBO) thin films (for x = 0, 0.02 and 0.05) for high-efficiency spintronics devices. For thin film of LCMBO (with x = 0.02), a significant increase in the magnetization and ferromagnetic ordering temperature (TC) are observed. Also, about 98% magnetoresistance (MR) and unusually large (~ 42%) anisotropic magnetoresistance (AMR) is observed at 50 K in the same LCMBO (for x = 0.02) thin film. This observed improvement in TC, MR and AMR in LCMBO (with x = 0.02) thin film may be attributed to the modulation of the trapped electrons through JT-distortions due to the replacement of Mn+3 ions by larger Bi+3 ions. With further increase in bismuth doping (for x = 0.05) at the B-site, a significant decrease in magnetization and TC have been observed.

cond-mat.mes-hall↗

arXiv2018

Structure, magnetic and transport properties of epitaxial thin films of equiatomic CoFeMnGe quaternary Heusler alloy

Future spintronics requires the realization of thin film of half-metallic ferromagnets having high Curie temperature and 100\% spin polarization at the Fermi level for potential spintronics applications. In this paper, we report the epitaxial thin films growth of half-metallic CoFeMnGe Heusler alloy on MgO (001) substrate using pulsed laser deposition system, along with the study of structural, magnetic and transport properties. The magnetic property measurements of the thin film suggest a soft ferromagnetic state at room temperature with an in-plane magnetic anisotropy and a Curie temperature well above the room temperature. Anisotropic magnetoresistance (AMR) ratio and temperature dependent electrical resistivity measurements of the thin film indicate the compound to be half-metallic in nature and therefore suitable for the fabrications of spintronics devices.

cond-mat.mtrl-sci↗

arXiv2017

Possible spin gapless semiconductor type behaviour in CoFeMnSi epitaxial thin films

Spin-gapless semiconductors with their unique band structures have recently attracted much attention due to their interesting transport properties that can be utilized in spintronics applications. We have successfully deposited the thin films of quaternary spin-gapless semiconductor CoFeMnSi Heusler alloy on MgO (001) substrates using a pulsed laser deposition system. These films show epitaxial growth along (001) direction and display uniform and smooth crystalline surface. The magnetic properties reveal that the film is ferromagnetically soft along the in-plane direction and its Curie temperature is well above 400 K. The electrical conductivity of the film is low and exhibits a nearly temperature independent semiconducting behaviour. The estimated temperature coefficient of resistivity for the film is -7x10^-10 Ohm.m/K, which is comparable to the values reported for spin-gapless semiconductors.

cond-mat.mtrl-sci↗

arXiv2017

Electron-quasiparticle interaction in $\rm DyNi_2B_2C$ measured by point-contact spectroscopy

The electron-quasiparticle interaction (EQI) spectral function has been measured for $\rm DyNi_2B_2C$ in the normal state at low temperatures by means of point-contact spectroscopy (PCS). A low-frequency peak is found around $eV\sim 5\ meV$. It becomes measurable at $T_m^*\simeq 15\ K$ and grows in intensity with constant width as the temperature is lowered. We argue that this peak arises from the strong interaction of conduction electron with coupled crystal-electric-field-phonon excitations whose branches cross at low energy. The comparison with PC spectra for $\rm HoNi_2B_2C$ suggests that a similar peak also exists for this compound. The magnitude of the point-contact EQI parameter $λ_{PC}$ for $\rm DyNi_2B_2C$ is estimated. $©$2000 Published by Elsevier Science B.V. All rights reserved.

cond-mat.supr-con↗

arXiv2017

Point-contact spectroscopy of superconducting energy gap in $\rm DyNi_2B_2C$

The superconducting energy gap in $\rm DyNi_2B_2C$ has been investigated using a point-contact technique based on the Andreev reflection from a normal (N)-superconductor (S) boundary, where N is Ag. The observed differential resistance $dV/dI$ is well described by the Blonder-Tinkham-Klapwijk (BTK) theory based on the BSC density of states with zero broadening parameter. Typically, the intensity of the gap structure amounts to several percentage of the normal state resistance, which is an order of magnitude less than predicted by the theory. For $\rm DyNi_2B_2C$ with $T_c<T_N$ (the Neel temperature), we found gap values satisfying the ratio of $2Δ_0/k_BT_c=3.63\pm 0.05$ similar to other superconducting nickel-borocarbides, both nonmagnetic and magnetic with $T_c\geq T_N$. The superconducting gap nonlinearity is superimposed on the antiferromagnetic structure in $dV/dI(V)$ which is suppressed at the magnetic field of the order of 3T applied nominally in the $ab$-plane and temperature $\geq 11~K$. The observed superconducting properties depend on the exact composition and structure at the surface of the crystal.

cond-mat.supr-con↗

arXiv2016

Coherent microwave generation by spintronic feedback oscillator

The transfer of spin angular momentum to a nanomagnet from a spin polarized current provides an efficient means of controlling the magnetization direction in nanomagnets. A unique consequence of this spin torque is that the spontaneous oscillations of the magnetization can be induced by applying a combination of a dc bias current and a magnetic field. Here we experimentally demonstrate a different effect, which can drive a nanomagnet into spontaneous oscillations without the need of external spin torque injection. For the demonstration of this effect, we use a nano-pillar of magnetic tunnel junction (MTJ) powered by a dc current and connected to a coplanar waveguide (CPW) lying above the free layer of the MTJ. Any fluctuation of the free layer magnetization is converted into oscillating voltage via the tunneling magneto-resistance effect and is fed back into the MTJ by the CPW through inductive coupling. As a result of this feedback, the magnetization of the free layer can be driven into a continual precession. The combination of MTJ and CPW behaves similar to a laser system and outputs a stable rf power with quality factor exceeding 10,000.

cond-mat.mes-hall↗

arXiv2016

Planar Hall and Nernst effect in patterned ultrathin film of La0.7Sr0.3MnO3

We present the observation of a transverse thermopower, or Planar Nernst Effect, in patterned ultrathin film (8 nm) of La0.7Sr0.3MnO3 (LSMO) driven by heat current applied in-plane of the film and Planar Hall Effect (PHE) in the same LSMO ultrathin film with in-plane current of 100 microA is also investigated. Even for temperature difference of 5 K the Planar Nernst Effect in ultrathin film (8 nm) shows a coercivity of 3 Oe same as observed in Planar Hall Effect measurement and confirms the ferromagnetic nature of thin film. The angular dependence of transverse voltages shows four-fold sin{theta} cos{theta} dependence symmetry at 250 K, which is consistent with Planar Hall Effect measurement.

cond-mat.mes-hall↗

arXiv2016

Magnetism in La$_{0.7}$Sr$_{0.3}$Mn$_{1-x}$Co$_x$O$_3$ ($0 \leq x \leq 1$)

We study the structural and magnetic properties of La$_{0.7}$Sr$_{0.3}$Mn$_{1-x}$Co$_x$O$_3$ ($0 \leq x \leq 1$). Rietveld refinement of X-ray Diffraction (XRD) pattern suggests phase purity of the polycrystalline samples with R$\bar{3}$c space group. Interplay of Ferromagnetic (FM) and Antiferromagnetic (AFM) interaction upon Co substitution at Mn site in La$_{0.7}$Sr$_{0.3}$MnO$_3$ is evident from magnetic measurements. There is an optimal cobalt substitution at which the coercive field is maximum.

cond-mat.mtrl-sci↗

arXiv2016

Extreme Sensitivity of Magnetic Properties on the Synthesis Routes in La$_{0.7}$Sr$_{0.3}$MnO$_3$

La$_{0.7}$Sr$_{0.3}$MnO$_3$ polycrystalline samples have been prepared using different synthesis routes. X-ray Diffraction (XRD) confirms that the samples are of single phase with R$\bar{3}$c space group. The surface morphology and particle size has been measured using Field Emission Scanning Electron Microscopy (FESEM). Magnetic measurement shows that the magnetization in the materials are affected by low crystallite size which destroys the spin ordering due to strain at grain boundaries and in turn also lead to reduction in magnetization as well as an enhanced coercivity in the material.

cond-mat.mtrl-sci↗

arXiv2016

n-type SnSe$_{1-x}$ for Thermoelectric Application

We report the synthesis of n-type SnSe$_{1-x}$ using a self-sacrificial, facile, solvo-thermal synthesis route. Electrical and thermal transport measurements suggest a low thermal conductivity and a significant thermopower in the temperature range 100 - 400\,K. We also propose the possibility of developing an all SnSe thermoelectric module.

cond-mat.mtrl-sci↗

arXiv2015

Electric Field Controlled Magnetization and Charge-Ordering in Pr0.6Ca0.4MnO3

In this paper, we present the observation of the electric field control on the charge-ordering and metamagnetic transitions during the magnetization measurements in a single crystal of Pr0.6Ca0.4MnO3 (PCMO). We have demonstrated that the complete melting of charge ordering can be realized in a single crystal of PCMO by applying a voltage as small as 2.5 V, which otherwise needs magnetic fields in excess of 11 T. The maximum change in magnetization with applied voltage occurs across the charge-ordering transition temperature (TCO = 235 K). Even though the electric field does not seem to affect the magnetic ordering, we see a clear evidence at low temperatures for the occurrence of the metamagnetic transitions at higher fields with the application of electric field.

cond-mat.mes-hall↗

arXiv2015

Cu2ZnSnS4 Films using an Eco-friendly Direct Liquid Coating Approach for Solar Cell Applications

Cu2ZnSnS4 (CZTS) is a promising candidate as an absorber material for thin film solar cells. The reported wet chemical synthesis approaches often have a high environmental impact due to the usage of abrasive solvents such as hydrazines, hydroxylamines, etc. We report an eco-friendly solvent based approach for making CZTS thin films with desirable absorption characteristics for solar cell applications.

cond-mat.mtrl-sci↗

arXiv2015

Electric field controlled magnetization and transport properties of La0.7Ca0.3MnO3 ultrathin film

We have investigated the effect of electric field control on the magnetization and the transport properties in La0.7Ca0.3MnO3 (LCMO) ultrathin film (~10 nm) by using it as the semiconductor channel material of a prototypical field effect device and SiO2 as dielectric gate. A large electroresistance (ER) of ~78% at Vg = -8 V is found in LCMO at 200 K. The direct magnetization measurements confirm the formation of a large ferromagnetic phase with the increase in the applied gate voltage at 200 K.

cond-mat.mes-hall↗