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Effect of Co substitution on the structural,electrical,and magnetic properties of Bi_(0.9)La_(0.1)FeO_3 by sol-gel synthesis

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International Journal of minerals,metallurgy and materials 2013年第2期20卷 166-171页

作者： Ghulam Ali Saadat A.Siddiqi shahid m.Ramay shahid Atiq murtaza Saleem Centre of Excellence in Solid State Physics University of the Punjab Interdisciplinary Research Centre in Biomedical materials COMSATS Institute of Information Technology Chemical Engineering Department College of EngineeringKing Saud University

Cobalt （Co）-doped ***3 multiferroics were synthesized by a sol-gel method based on the auto- combustion technique. As-synthesized powder was examined using various characterization techniques to explore the effect of Co substitution on the properties of Bi0.9La0.1FeO3. X-ray diffraction reveals that Co-doped Bi0.9La0.1FeO3 preserves the perovskite-type rhombohedral structure of BiFeO3, and the composition without Co preserves the original structure of the phase; however, a second-phase Bi2Fe409 has been identified in all other compositions. Surface morphological studies were performed by scanning electron microscopy. Temperature-dependent resistivity of the samples reveals the characteristic insulating behavior of the multiferroic material. The resistivity is found to decrease with the increase both in temperature and Co content. Room temperature frequency-dependent dielectric measurements were also reported. magnetic measurements show the enhancement in magnetization with the increase in Co content.

关键词： multiferroics cobalt doping microstructure electric properties magnetic properties sol-gel process

Enhancing secrecy rates in a wiretap channel

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Digital Communications and Networks 2020年第1期6卷 129-135页

作者： shahid m.Shah Vinod Sharma Department of ECE Indian Institute of ScienceBangalore560012India

Reliable communication imposes an upper limit on the achievable rate,namely the Shannon ***'s wiretap coding ensures a security constraint and reliability,but results in a decrease of achievable *** mitigate the loss in secrecy rate,we propose a coding scheme in which we use sufficiently old messages as key and prove that multiple messages are secure with respect to all the information possessed by the *** also show that we can achieve security in the strong ***,we study a fading wiretap channel with full channel state information of the eavesdropper's channel and use our coding/decoding scheme to achieve a secrecy capacity close to the Shannon capacity of the main channel(in the ergodic sense).Finally,we study a case where the transmitter does not have instantaneous information of the channel state of the eavesdropper,but only its distribution.

关键词： Physical layer security Rate loss Secret key Wiretap channel Secrecy capacity

Origin of Ferromagnetism in Al and Ni Co-doped ZnO Based DmS materials

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Chinese Physics Letters 2012年第10期29卷 155-157页

作者： murtaza Saleem Saadat A.Siddiqi shahid m.Ramay shahid Atiq Shahzad Naseem Centre for Solid State Physics University of the PunjabQuaid-e-Azam CampusLahore 54590Pakistan 2Interdisciplinary Research Centre in Biomedical MaterialsCOMSATS Institute of Information TechnologyDefence RoadOff Raiwind RoadLahorePakistan 3Department of Chemical EngineeringCollege of EngineeringKing Saud UniversityP.O.Box 800Riyadh 11421Saudi Arabia

Zn0.95Ni0.05O and Zn0.90Ni0.05Al0.05O compositions of nanocrystallites are synthesised using the well recognised auto-combustion *** x-ray diffraction patterns demonstrate the phase pure characteristic wurtzite-type crystal structure with space group P63mc in both the *** elemental incorporation of Ni and Al contents into the ZnO structure is confirmed by energy dispersive x-ray *** micrographs of scanning electron microscopy show an approximate ordered *** electrical resistivity is observed to decrease with the rising temperature,depicting the characteristic semiconductor behaviour of the *** lower values of resistivity and ferromagnetic interactions in the Al-doped sample correspond to an increase of carrier's *** is observed that the carrier mediated mechanism is mainly responsible for ferromagnetism in ZnO-based diluted magnetic semiconductors.

关键词： resistivity diluted Origin

Theoretical investigation of optical properties and band gap engineering for Zn1-xTmxTe(Tm=Fe,Co)alloys by modified Becke-Johnson potential

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Chinese Physics B 2017年第8期26卷 491-498页

作者： Q mahmood m Yaseen m Hassan shahid m Ramay Asif mahmood materials Growth and Simulation Laboratory Department of PhysicsUniversity of the PunjabQuaid-i-Azam Campus54590LahorePakistan Department Of Physlcs University of Agriculture UniversityFaisalabad 38040Pakistan Physics and Astronomy Department College of ScienceKing Sand UniversityRiyadhSaudi Arabia Chemical Engineering Department College of EngineeringKing Saud UniversityRiyadhSaudi Arabia

The direct band gap ZnTe with transition metal （Tm） impurities plays a vital role in optoelectronic and spintronic applications. In the present study, we use the advanced modified Becke-Johnson （mBJ） functional for performing the structural computations and detailed investigations of the optical characters in Zn1_xTmxTe （Tm = Fe, Co） alloys with 0 ≤ x ≤1. By employing the FP-LAPW method, we determine various optical parameters for the ternary alloys and for the end binaries. The calculated static dielectric constants and optical band gaps for Zn1_xTmxTe （Tm = Fe, Co） have an inverse relation that verifies the Penn model. We find that the static dielectric constant is nearly equal to the square of the static refractive index, and both increase with Tm content. Furthermore, we also find a slight shift of peaks to a higher energy region with increasing Tm concentration. The decreasing band gap and high value of the absorption in the visible region of electromagnetic spectrum make these alloys suitable for photonic and solar cell applications.

关键词： amorphous semiconductors transition metal-doped ZnTe structural computation optical property

Ab-initio calculations of bandgap tuning of In1-xGaxY(Y=N,P)alloys for optoelectronic applications

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Chinese Physics B 2021年第11期30卷 467-474页

作者： muhammad Rashid Jamil m mahmood Q shahid m Ramay Asif mahmood A Ghaithan H m Department of Physics Ghazi University City CampusDera Ghazi Khan32200Pakistan Department of Physics COMSATS University IslamabadIslamabad 44000Pakistan Basic and Applied Scientific Research Center(BASRC) College of Science of DammamImam Abdulrahman Bin Faisal UniversityP.O.Box 383Dammam 31113Saudi Arabia Department Physics College of ScienceImam Abdulrahman Bin Faisal UniversityP.O.Box 1982Dammam 31441Saudi Arabia Physics and Astronomy Department College of ScienceKing Saud UniversityRiyadhSaudi Arabia Chemical Engineering Department College of EngineeringKing Saud UniversityRiyadhSaudi Arabia

The III–V alloys and doping to tune the bandgap for solar cells and other optoelectronic devices has remained a hot topic of research for the last few *** the present article,the bandgap tuning and its influence on optical properties of In1-xGaxN/P,where(x=0.0,0.25,0.50,0.75,and 1.0)alloys are comprehensively analyzed by density functional theory based on full-potential linearized augmented plane wave method(FP-LAPW)and modified Becke and Johnson potentials(TB-mBJ).The direct bandgaps turn from 0.7 eV to 3.44 eV,and 1.41 eV to 2.32 eV for In1-xGaxN/P alloys,which increases their potentials for optoelectronic *** optical properties are discussed such as dielectric constants,refraction,absorption,optical conductivity,and *** light is polarized in the low energy region with minimum *** absorption and optical conduction are maxima in the visible region,and they are shifted into the ultraviolet region by Ga ***,static dielectric constant e1(0)is in line with the bandgap from Penn’s model.

关键词： density functional theory direct bandgap III-V semiconductors tuning of optical band gap solar cell applications

Competing crystallite size and zinc concentration in silica coated cobalt ferrite nanoparticles

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Progress in Natural Science:materials International 2014年第3期24卷 199-204页

作者： K.Nadeem m.shahid m.mumtaz materials Research Laboratory Department of Physics International Islamic University

Silica coated(30 wt%) cobalt zinc ferrite(Co1 xZnxFe2O4, x?0, 0.2, 0.3, 0.4, 0.5 and 1) nanoparticles were synthesized by using sol–gel method. Silica acts as a spacer among the nanoparticles to avoid the agglomeration. X-ray diffraction(XRD) reveals the cubic spinel ferrite structure of nanoparticles with crystallite size in the range 37–45 nm. Fourier transform infrared(FTIR) spectroscopy confirmed the formation of spinel ferrite and SiO2. Scanning electron microscopy(SEm) images show that the nanoparticles are nearly spherical and non-agglomerated due to presence of non-magnetic SiO2 surface coating. All these measurements signify that the structural and magnetic properties of Co1 xZnxFe2O4 ferrite nanoparticles strongly depend on Zn concentration and nanoparticle average crystallite size in different Zn concentration regimes.& 2014 Chinese materials Research Society. Production and hosting by Elsevier B.V. All rights reserved.

关键词： Ferrite Nanoparticles Composites magnetic properties

magnetism,optical,and thermoelectric response of CdFe_2O_4by using DFT scheme

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Chinese Physics B 2018年第3期27卷 376-383页

作者： Q mahmood m Yaseen K C Bhamu Asif mahmood Y Javed shahid m Ramay materials Growth and Simulation Laboratory Department of PhysicsUniversity of the Punjab Department of Physics University of AgricultureFaisalabad Department of Physics Goa University Chemical Engineering Department College of Engineering King Saud University Physics and Astronomy Department College of Science King Saud University

Comparative analysis of electronic, magnetic, optical, and thermoelectric properties of CdFe2O4, calculated by em- ploying PBEsol ＋ mBJ has been done. The PBEsol reveals metallic nature, while TB-mBJ illustrates ferromagnetic semiconducting behavior. The reasons behind the origin of ferromagnetism are explored by observing the exchange, crystal field, and John-Teller energies. The optical nature is investigated by analyzing dielectric constants, refraction, absorption coefficient, reflectivity, and optical conductivity. Finally, thermoelectric properties are elaborated by describing the electri- cal and thermal conductivities, Seebeck coefficient, and power factor. The strong absorption for the visible energy and high power factor suggest CdFe2O4 as the potential candidate for renewable energy applications.

关键词： frustrated magnetism density functional theory John-Teller distortion Hund's rule

Bandgap engineering to tune the optical properties of Be_xmg_(1-x)X(X=S, Se, Te) alloys

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Chinese Physics B 2018年第1期27卷 415-423页

作者： B Sabir N A Noor m Rashid Fasih Ud Din shahid m Ramay Asif mahmood Centre for Advanced Studies in Physics Government College University Department of Physics School of Science University of Management and TechnologyLahore Pakistan Department of Physics COMSATS Institute of Information Technology Physics and Astronomy Department College of Science King Saud University Chemical Engineering Department College of Engineering King Saud University

Structural, electronic, and optical properties of alloys Bexmgl-xX （X = S, Se, Te） in the assortment 0 〈 x 〈 1 were theoretically reported for the first time in zinc-blende （ZB） phase. The calculations were carried out by using full-potential linearized augmented plane wave plus local orbitals （FP-LAPW＋lo） formalism contained by the framework of density functional theory （DFT）. Wu--Cohen （WC） generalized gradient approximation （GGA）, based on optimization energy, has been applied to calculate these theoretical results. In addition, we used Becke and Johnson （mBJ-GGA） potential, modified form of GGA functional, to calculate electronic structural properties up to a high precision degree. The alloys were composed with the concentrations x = 0.25, 0.5, and 0.75 in pursuance of ＇special quasi-random structures＇（SQS） approach of Zunger for the restoration of disorder around the observed site of alloys in the first few shells. The structural parameters have been predicted by minimizing the total energy in correspondence of unit cell volume. Our alloys established direct band gap at different concentrations that make their importance in optically active materials. Furthermore, density of states was discussed in terms of the contribution of Be and mg s and chalcogen （S, Se, and Te） s and p states and observed charge density helped us to investigate the bonding nature. By taking into consideration of immense importance in optoelectronics of these materials, the complex dielectric function was calculated for incident photon energy in the range 0--15 eV.

关键词： Bexmgl-xX (X = S Se Te) alloys zinc-blende (ZB) phase density functional theory (DFT),electronic and optical properties

Ab-initio investigation of AGeO_3(A=Ca, Sr) compounds via Tran Blaha-modified Becke Johnson exchange potential

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Chinese Physics B 2017年第11期26卷 375-382页

作者： Rasul Bakhsh Behram m A Iqbal muhammad Rashid m Atif Sattar Asif mahmood shahid m Ramay Physics Department University of the Punjab Quaid-e-Azam Campus Allama Iqbal Open University Regional Campus Department of Physics School of Science University of Management and Technology Department of Physics COMSATS Institute of Information Technology Department of Physics Simulation Lab The Islamia University of Bahawalpur Chemical Engineering Department College of Engineering King Saud University Physics and Astronomy Department College of Science King Saud University

We employ ab-initio calculations to analyze the mechanical, electronic, optical and also thermoelectric properties associated with AGeO3（A = Ca, Sr） compounds. The full-potential linearized augmented plane wave（FP-LAPW） technique in the generalized gradient approximation（GGA-PBEsol） and the lately designed Tran-Blaha-modified Becke-Johnson exchange potential are utilized to examine the mechanical and optoelectronic properties respectively. To explore the thermoelectric quality, we use the semi-classical Boltzmann transport theory. The particular structural stabilities regarding AGeO3（A = Ca, Sr） materials are validated simply by computations from the elastic constants. The energy band structural framework and the density of states are displayed to indicate indirect bandgap under ambient conditions. The particular computed optical attributes that reveal prospective optoelectronic applications are usually elucidated simply by studying ε1（0） and also Eg, which can be connected by means of Penn＇s design. The optical details uncover the actual suitability to power ranging products. Finally, the Boltz Tra P code is executed to analyze the actual thermoelectric properties, which usually presents that the increase of internal temperatures can enhance the electric conductivity, thermal conductivity and also the power factor, whilst Seebeck coefficient decreases. Therefore, the studied materials will also be ideal for thermoelectric products to understand helpful option for alternative energy resources.

关键词： semiconductors elastic properties optical properties thermal properties