gopi kaphle

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Dr. Gopi Chandra Kaphle is an Associate Professor of Tribhuvan University. He received his Ph.D. in Physics from Tribhuvan University in 2014. He has 17 years of experience in Physics research, teaching and training. To his credit, Dr. Kaphle has published over 25 research articles and two books. His major contribution is on the Condensed Matter Physics, Solid state physics, statistical Physics, Nano-materials and computational Physics. He also has collaborative work in India and German related to research in Material sciences which ultimately help to developed the field of Science and Technology in Nepal.Dr. Kaphle is an active member of several organization related to Science and Technology like Nepal Physical Society

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First-principles study of the electronic and optical properties of the (Y, N)-codoped anatase TiO 2 photocatalyst

Chinese Physics B, 2012

First-principles plane-wave pseudopotential calculations are performed to study the geometrical s... more First-principles plane-wave pseudopotential calculations are performed to study the geometrical structures, formation energies, and electronic and optical properties of Y-doped, N-doped, and (Y, N)-codoped TiO2. The calculated results show that Y and N codoping leads to lattice distortion, easier separation of photogenerated electron-hole pairs and band gap narrowing. The optical absorption spectra indicate that an obvious red-shift occurs upon Y and N codoping, which enhances visible-light photocatalytic activity.

Electronic structure and magnetic phase transition in MnSi

Physics of the Solid State, 2017

Hexagonal FeSe thin films were grown on SrTiO 3 substrates and the temperature and thickness depe... more Hexagonal FeSe thin films were grown on SrTiO 3 substrates and the temperature and thickness dependence of their electronic structures were studied. The hexagonal FeSe is found to be metallic, with a Fermi surface consisting of six elliptical electron pockets. With decreased temperature, parts of the bands shift downward to high binding energy while some bands shift upward to E F . The shifts of these bands begin around 300 K and saturate at low temperature, indicating a magnetic phase-transition temperature of about 300 K. With increased film thickness, the Fermi surface topology and band structure show no obvious change. Our paper reports the electronic structure of hexagonal FeSe, and shows that the possible magnetic transition is driven by large-scale electronic structure reconstruction.

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Editorial Vol.4(1)

Journal of Nepali Physical Society, May 22, 2017

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Experimental and Theoretical Study on Electronic and Optical Properties of TiO2 (anatase) Bulk and Al Doped Thin Film Phases

Journal of Lumbini Engineering College, Nov 22, 2023

Tuning the electronic and optical properties of TiO2is very important because of the variety of a... more Tuning the electronic and optical properties of TiO2is very important because of the variety of applications, including photocatalysts, electronics and data storage devices, and solar cells. Here, we performed the theoretical and experimental investigation of electronic, and optical properties of TiO2and Al doped TiO2in the form of bulk and thin film.A tight binding linear muffintin orbital(TB-LMTO) approach is used to optimized the TiO2 (anatase) in bulk phase. The optimized lattice parameter of TiO2 (anatase) is found to be 3.89Å.The band structure plot reveals that bulk TiO2 (anatase) bears wide bandgap semiconducting behavior with bandgap (Eg) 3.23 eV whereas thin film of aluminium doped TiO2 (anatase) behaves as a metal. The symmetric nature of up and down density of state (DOS) and projected density of states (PDOS) for both bulk and thin film of TiO2 (anatase) ensures their non-magnetic behavior. Experimental observation shows that the surface reflectance of the film increases with increasing concentration of aluminium (Al) while transmittance observed as opposite trends. The direct and indirect bandgaps of TiO2film evaluated using transmittance curves are 3.53 eV and 3.27 eV respectively, which are well agreed with the available standard band-gap range of TiO2 film (3.2 eV to 3.65 eV). The direct band gaps for Al-1% and Al-3% doped TiO2film are 3.60 eV and 3.62 eV respectively with thickness obtained from swanepoel method are 682.06 nm and 745.56 nm respectively.

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Unraveling the structural, electronic and magnetic properties of Mn1Pd n-1, Mn 2Pd n-2 and Pd n(n=13) clusters

Pragya Darshan प्रज्ञा दर्शन, Nov 1, 2023

This work presents a systematic study of the geometric, electronic and magnetic properties of Pd ... more This work presents a systematic study of the geometric, electronic and magnetic properties of Pd clusters pristine and mono-and bidoped with Mn: Pdn, Pdn−1Mn, Pdn−2Mn 2 where n ≤13. We have used the density functional formalism with the spin polarized generalized gradient approximation. From the variety of possible structures with thirteen atoms, we found the icosahedral configuration to be the most stable as compared to the hexagonal, cub-octahedral and buckled bi-planar. The change in magnetic behavior of Pd clusters after doping with Mn has been observed. This communication is an attempt to understand that behaviour.

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Structural, Electronic and Magnetic Properties of XYZ Type Half-Heusler Alloys

Journal of Nepali Physical Society, Dec 29, 2019

The spintronic devices have played an important role in modern technological era. Heusler alloys ... more The spintronic devices have played an important role in modern technological era. Heusler alloys have attracted lot of interest in spintronic applications due to their half-metallic properties predicted by band structure calculations. We investigate the electronic, magnetic and structural properties of half-Heusler alloys FeMnGe and CoMnSb using first principles based density functional theory (DFT) implemented on Tight Binding Linear Muffin-Tin Orbital within Atomic Sphere Approximation (TB-LMTO-ASA) code. The calculation reveal that CoMnSb and FeMnGe are half-metallic Ferro-magnet in nature of with magnetic moment 1.00 µB and 2.99 µB per formula unit at equilibrium lattice parameter respectively. The magnetic moment mainly originates from the strong spin polarization of d electrons of X atom and partial contribution of p electrons of Y atom. The half metallic gap of FeMnGe and CoMnSb is found to be 0.38 eV and 0.95 eV respectively. This shows that these alloys are very promising spintronic functional materials.

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$Research paper thumbnail of Structural Identification of Cubic Aluminum and Non-Cubic Titanium using X-Ray Diffractometer$

Structural Identification of Cubic Aluminum and Non-Cubic Titanium using X-Ray Diffractometer

The unknown crystalline samples like minerals, inorganic compounds etc. are identified mostly wit... more The unknown crystalline samples like minerals, inorganic compounds etc. are identified mostly with the help of X-ray diffraction (XRD). More than 25 Nobel prizes have been awarded to the works based on it. The identification of the solids are essential for the research in various streams of science like Material, Environmental, Geo, Engineering and Biology. The XRD is based on Bragg's law. The diffraction pattern obtained after passing the X-ray through interatomic slit is the main source of the structure. It was first demonstrated by Max von Laue (1912). The XRD is now attached with instrumental and computational tools. This paper focus on different steps for the indexing of an X-ray diffraction pattern, identifying the Bravais lattice, and calculating the lattice parameters of the cubic (Al) and non-cubic (Ti) system that are the starting elements we have used for the preparation of MXene. We have used the experimental and mathematical ways for the determinations of the intended structural values. The values obtained were in well agreement with the standard data.

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Electronic and Magnetic Properties of Half Metallic Heusler Alloy Co2mnsi: A First-Principles Study

The himalayan physics, Oct 12, 2017

Heusler alloys have been of great interest because of their application in the field of modern te... more Heusler alloys have been of great interest because of their application in the field of modern technological word. Electronic and magnetic properties of Co, Mn, Si and the Heusler alloy Co 2 MnSi have been studied using Density functional theory based Tight Binding Linear Muffin Tin Orbital with Atomic Sphere Approximation (TB-LMTO-ASA) approach. From the calculation lattice parameter of optimized structure of Co, Mn, Si and Co2MnSi are found to be 2.52A0 , 3.49A0 , 5.50A0 , 5.53A0 respectively. Band structure calculations show that Co and Mn are metallic, Si as semi-conducting while the Heusler alloy Co 2 MnSi as half-metallic in nature with band gap 0.29eV. The charge density plot indicates major bonds in Co 2 MnSi are ionic in nature. Magnetic property has been studied using the density of states (DOS), indicating that Co and Co 2 MnSi are magnetic with magnetic moment 2.85µ B and 4.91µ B respectively. The contribution of orbitals in band, DOS and magnetic moment are due to d-orbitals of Co and Mn and little from s and p-orbital of Si in Co 2 MnSi.

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Effect of Mn Doping on the Electronic and Magnetic Properties of Full Heusler Alloy Co2FeSi

Journal of Lumbini Engineering College

Heusler compounds are one of the largest families of ternary intermetallics with broad range of a... more Heusler compounds are one of the largest families of ternary intermetallics with broad range of applications. In this work, we inspected the electronic and magnetic properties of full Heusler alloy Co2FeSi and the effect induced by doping Mn atom on those properties. We employed plane wave pseudo-potential method based on DFT framework implemented in Quantum ESPRESSO code using PBE type of functional for exchange correlation energy. The calculation demonstrates that Co2FeSi exhibits metallic nature in the majority spin state and semi-conducting nature in minority spin state with indirect energy gap of ≈ 0.132 eV and shows chances of weakened half-metallicity as indicated by the presence of band gap below fermi level. The calculated total magnetic moment is 5.44 μB/cell which is found to be deviated from Slater-Pauling rule M = NV − 24 for full Heusler compounds. The site selection for doping was based on the empirical rule for atomic occupation established for Heusler alloys and the...

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Structural, electronic, and magnetic properties of quaternary Heusler compounds, CoFeTiSb and CoMnCrSi: A First-principles study

Materials Today: Proceedings, 2021

ATB-LMTO approach to study structural stability and electronic behavior of transition metal dichalcogenides MX2 (M=Zr,HfANDX=S,Se)

Himalayan Physics, 2019

We present a comprehensive first principles study on structural and electronic properties of TMDs... more We present a comprehensive first principles study on structural and electronic properties of TMDs MX 2 (M=Zr, Hf AND X=S, Se) using Local Density Approximation (LDA) implemented Tight Binding Linear Muffin Tin Orbital (TB-LMTO) approach. The structural optimization of these materials are performed using energy minimization process. The optimized lattice parameters for ZrS 2 , ZrSe 2 , HfS 2 and HfSe 2 are found to be 3.71 A, 3.70Å, 3.62Å, and 3.80Årespectively. The band gaps of these materials are found to be 1.75 eV, 1.139 eV, 2.04 eV and 1.134 eV respectively which reveals the semi-conducting nature of ZrS 2 , ZrSe 2 and HfSe 2 while HfS 2 is found to be insulator with large band gap. The density of states of these materials for up-spin and down-spin are found to be symmetric in nature showing non-magnetic behavior of these materials. The charge density plot of these materials along (100)plane and (110) plane shows covalent bond exist among (X-X) and (M-X) atoms while ionic bond exist among (M-M) atoms.

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Magnetic Moment of Zigzag CuO Nanotubes at Different Temperature and Size: Ab-Initio Study

Journal of Materials Science and Nanotechnology, Jun 1, 2018

In the past few years' investigation in the magnetic properties with different aspect in nano str... more In the past few years' investigation in the magnetic properties with different aspect in nano structure have been increased rapidly because of their technological importance, lots of attractive properties like, high surface-volume ratio, electronic, optical and magnetic properties as well as for understanding the physics involved in their many unusual properties comparing with the bulk [1-5]. Since, the discovery of the high temperature superconductor in copper oxide peroviskit and its unique electric and magnetic properties, Copper oxide (CuO) got more attention and made more interesting candidate for research [6-8]. Our recent ab-intio investigation on magnetism in zigzag and armchair CuO nanotubes shows remarkable magnetic properties at different diameter [9]. So, it is wrathful to investigate the temperature and size dependent magnetic properties in zigzag CuO nano tubes as a function of temperature.

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Study of Electronic Structure and Topological Phenomena in Ti 2 N MXene

Bulletin of the American Physical Society, Mar 18, 2021

DFT Analysis of Ferromagnetism in Zigzag and Armchair CuO Nanosheets

Physics of the Solid State, Aug 1, 2020

We report the structural, electronic, and magnetic properties of "zigzag" and "armchair" CuO nano... more We report the structural, electronic, and magnetic properties of "zigzag" and "armchair" CuO nanosheets. The density function theory (DFT)-based ab initio approach has been applied through revised Perdew, Burke, and Ernzerhof (rPBE) parameterized spin generalized-gradient approximation (SGGA) + mean-field Hubbard correction (U) exchange-correlation functional. In comparison to the semiconducting bulk CuO, the other forms of CuO nanosheets show metallic behavior and their structural stabilities have been analyzed through binding energy estimation. Using SGGA, the computed magnetic moment per atom of zigzag CuO nanosheet varies irregularly between 0.66 and 1.19 μ B , whereas for armchair CuO, between 0.59 and 1.53 μ B. The addition of U changes this variation from 0.68 to 0.76 μ B in zigzag and from 0.62 to 1.29 μ B in armchair nanosheets, respectively. The computed spin polarization as unity or less than unity identifies the ferromagnetism in these materials. Obtained results of CuO nanosheets defend them as a potential candidate for a variety of electronic devices like gas sensors, electrodes, energy storage devices, etc.

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Magnetism in Zigzag and Armchair CuO Nanoribbons: Ab Initio Analysis

Physics of the Solid State, Feb 1, 2021

Abstract The present work reports the magnetism analysis of zigzag and armchair forms of CuO nano... more Abstract The present work reports the magnetism analysis of zigzag and armchair forms of CuO nanoribbons by using density functional theory (DFT)-based ab initio approach. The structural stability has been confirmed through the binding energy calculation. The electronic and magnetic properties have been analyzed as a function of varied width of CuO nanoribbons, interesting information for variety of applications. The metallic and ferromagnetic behaviors of CuO nanoribbons are observed, whereas its bulk counterpart shows a p-type semiconducting and antiferromagnetic nature. The computed magnetic moments for the zigzag and armchair forms of CuO nanoribbon are in the ranges of 0.19–0.61 μ B and 0.24–0.97 μ B , respectively. The computed spin polarizations confirms the half or full metallic ferromagnetic nature of these nanoribbons.

Electronic Structures and Magnetic Properties of NiAl and Ni3Al

Quantum matter, Jun 1, 2016

The adsorption characteristics of transition metal (TM) adatoms on olympicene, a graphene-like mo... more The adsorption characteristics of transition metal (TM) adatoms on olympicene, a graphene-like molecule consisting of five rings of which four are benzene-like rings, are analyzed by means of firstprinciples calculations. The electronic structures and magnetic properties of 3d transition metals on olympicene were investigated in the framework of generalized-gradient approximation using relativistic density functional theory. Our calculations were based on full-potential local orbital (FPLO) method. Stable structure and total energies were obtained. Relaxed TM@Olympicene molecules, unlike the pure organic olympicene, were partially buckled. Binding energy calculations showed high stability for Ni@Olympicene whereas Mn did not bind to olympicene surface. Electronic charge transfers were consistent with Pauling electronegativities. The related HOMO-LUMO gaps decreased with respect to pure olympicene. Our calculated total and TM spin magnetic moments indicated that TM@Olympicene were strongly magnetized. Orbital polarization correction (OPC) were also used in order to get an upper estimation for orbital magnetic moment of all 3d atoms. Fe@Olympicene shows highest orbital moment of 0.18 m B. The Atoms in Molecules (AIM) approach was used to analyze the nature of TMeC bonds in TM@Olympicene complexes. The results show the TMeC bonds have a degree of covalency in their interactions.

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Spin reorientation in antiferromagnetic Dy2FeCoO6 double perovskite

Journal of Physics: Condensed Matter, Oct 15, 2020

We explored the electronic and magnetic properties of the lanthanide double perovskite Dy2FeCoO6 ... more We explored the electronic and magnetic properties of the lanthanide double perovskite Dy2FeCoO6 by combining magnetization, Raman and Mössbauer spectroscopy and neutron diffraction along with density functional theory (DFT) calculations. Our magnetization measurements revealed two magnetic phase transitions in Dy2FeCoO6. First, a paramagnetic to antiferromagnetic transition at T N = 248 K and subsequently, a spin reorientation transition at T SR = 86 K. In addition, a field-induced magnetic phase transition with a critical field of H c ≈ 20 kOe is seen at 2 K. Neutron diffraction data suggested cation-disordered orthorhombic structure for Dy2FeCoO6 in Pnma space group which is supported by Raman scattering results. The magnetic structures ascertained through representational analysis indicate that at T N, a paramagnetic state is transformed to Γ5(Cx, Fy, Az) antiferromagnetic structure while, at T SR, Fe/Co moments undergo a spin reorientation to Γ3(Gx, Ay, Fz). The refined magnetic moment of (Fe/Co) is 1.47(4) μ B at 7 K. The antiferromagnetic structure found experimentally is supported through the DFT calculations which predict an insulating electronic state in Dy2FeCoO6.

Electronic and Magnetic Properties of Double Perovskites Nd2MgIrO6

Journal of Nepali Physical Society, Jan 28, 2016

We have studied the electronic and magnetic properties of double perovskites Nd 2 MgIrO 6 by mean... more We have studied the electronic and magnetic properties of double perovskites Nd 2 MgIrO 6 by means of full-potential linearized augmented plane wave (FP-LAPW) method based on density-functional theory (DFT). For the exchange-correlation potential, generalized gradient approximation (GGA) has been used. Based on our DFT calculations, Nd 2 MgIrO 6 is found to have an antiferromagnetic (AFM) ground state. The material shows Mott-Hubbard type insulator, which is observed to occur due to strong correlation in Nd-4f and Ir-5d states in addition to large crystal distortion, observed in the system. Strong hybridization between O-2p, Ir-5d and Nd-4f electrons are observed from the density of states findings. Our results shows that the 5d electrons of Ir hybridize strongly with O-2p states close to the Fermi level giving rise to the insulating state with a Mott-gap of ~0.9 eV in Nd 2 MgIrO 6. Our study suggests that the total magnetic moment reduces to 5.0 μ B per formula unit as a result of itinerant super-exchange rather than the exchange interaction involving individual ions of Nd and Ir atoms.

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Strain induced electronic structure, and magnetic and structural properties in quaternary Heusler alloys ZrRhTiZ (Z = Al, In)

Journal of Alloys and Compounds, Jun 1, 2021

Abstract Electronic structure, and magnetic and structural properties of quaternary Heusler alloy... more Abstract Electronic structure, and magnetic and structural properties of quaternary Heusler alloys ZrRhTiZ (Z = Al, In) have been analyzed from first principles calculations. The ferromagnetic ground state and thermodynamical stability of these compounds are supported by relative total energies, and by derived formation and cohesive energies, respectively. The investigated Curie temperatures of the compounds exceed room temperature indicating that these compounds are promising candidates for beyond room temperature spintronics and magneto-electronics applications. Both compounds follow the Slater-Pauling 18 electron rule and exhibit half-metallic ferromagnetic behavior with magnetic moments of 2 μB with 100 % spin polarization in one spin channel at the Fermi-level. The effect of uniform strain on half-metallicity of these compounds inverts the band gap from one spin channel to another spin channel with a mixed spin (magnetic moment) regime that can be mapped to an exchange bias like effect observed in some of the magnetic Heusler compounds. The half metallic ferromagnetic behavior is retained within -2% to 2% strain contrasting with the anomalous spin flip in -1% and 1% strain in ZrRhTiZ (Z= Al, In).

Magnetoelectronic and optical properties of CoMnZnSi quaternary Heusler alloy

Bulletin of the American Physical Society, Mar 18, 2021

Magnetoelectronic and optical properties of carbon nanotubes are, respectively, studied within th... more Magnetoelectronic and optical properties of carbon nanotubes are, respectively, studied within the sp 3 tight-binding model and the gradient approximation. They strongly depend on the magnitude and the direction of the magnetic field, the nanotube geometry ͑radius and chiral angle͒, and the Zeeman splitting. The magnetic field would lead to the change of energy gap, the destruction of state degeneracy, and the coupling of different angular momenta. Hence there are magnetic-field-dependent absorption frequencies and more absorption peaks. The types of carbon nanotubes predominate in the band structure and thus the range of absorption frequencies and the number of absorption peaks. The Zeeman splitting makes the semiconductor-metal transition occur at lower magnetic flux. It metalizes armchair carbon nanotubes in the presence of the perpendicular magnetic field. However, it does not affect the optical excitations except for metallic carbon nanotubes.

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