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Ramzan, Muhammad
Alternative names
Publications (10 of 43) Show all publications
Arslanov, T. R., Mollaev, A. Y., Kamilov, I. K., Arslanov, R. K., Kilanski, L., Minikaev, R., . . . Shoukavaya, T. V. (2015). Pressure control of magnetic clusters in strongly inhomogeneous ferromagnetic chalcopyrites. Scientific Reports, 5, 7720
Open this publication in new window or tab >>Pressure control of magnetic clusters in strongly inhomogeneous ferromagnetic chalcopyrites
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2015 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, p. 7720-Article in journal (Refereed) Published
Abstract [en]

Room-temperature ferromagnetism in Mn-doped chalcopyrites is a desire aspect when applying those materials to spin electronics. However, dominance of high Curie-temperatures due to cluster formation or inhomogeneities limited their consideration. Here we report how an external perturbation such as applied hydrostatic pressure in CdGeP2:Mn induces a two serial magnetic transitions from ferromagnet to non-magnet state at room temperature. This effect is related to the unconventional properties of created MnP magnetic clusters within the host material. Such behavior is also discussed in connection with ab initio density functional calculations, where the structural properties of MnP indicate magnetic transitions as function of pressure as observed experimentally. Our results point out new ways to obtain controlled response of embedded magnetic clusters.

National Category
Other Physics Topics
Identifiers
urn:nbn:se:uu:diva-244484 (URN)10.1038/srep07720 (DOI)000347813700001 ()
Available from: 2015-02-25 Created: 2015-02-17 Last updated: 2017-12-04Bibliographically approved
Araujo, C. M., Nagar, S., Ramzan, M., Shukla, R., Jayakumar, O. D., Tyagi, A. K., . . . Rao, K. V. (2014). Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites. Scientific Reports, 4, 4686
Open this publication in new window or tab >>Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites
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2014 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, p. 4686-Article in journal (Refereed) Published
Abstract [en]

We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spectroscopic techniques and first-principles calculations. We find that the observed order-disorder transformation is accompanied by an insulator-metal transition arising from a wide distribution of Cr-O-Cr bond angles and the consequent metallization through free carriers. Similar results also found in YbCrO3-films suggest that the observed phenomenon is more general and should, in principle, apply to a wider range of oxide systems. The ability to tailor ferromagnetic order above room temperature in oxide materials opens up many possibilities for novel technological applications of this counter intuitive effect.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-204955 (URN)10.1038/srep04686 (DOI)000334286200001 ()
Available from: 2013-08-13 Created: 2013-08-13 Last updated: 2017-12-06Bibliographically approved
Lykissa, I., Li, S.-Y., Ramzan, M., Chakraborty, S., Ahuja, R., Granqvist, C. G. & Niklasson, G. A. (2014). Electronic density-of-states of amorphous vanadium pentoxide films: Electrochemical data and density functional theory calculations. Journal of Applied Physics, 115(18), 183701/1-/5
Open this publication in new window or tab >>Electronic density-of-states of amorphous vanadium pentoxide films: Electrochemical data and density functional theory calculations
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2014 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 18, p. 183701/1-/5Article in journal (Refereed) Published
Abstract [en]

Thin films of V2O5 were prepared by sputter deposition onto transparent and electrically conducting substrates and were found to be X-ray amorphous. Their electrochemical density of states was determined by chronopotentiometry and displayed a pronounced low-energy peak followed by an almost featureless contribution at higher energies. These results were compared with density functional theory calculations for amorphous V2O5. Significant similarities were found between measured data and computations; specifically, the experimental low-energy peak corresponds to a split-off part of the conduction band apparent in the computations. Furthermore, the calculations approximately reproduce the experimental band gap observed in optical measurements.

National Category
Condensed Matter Physics Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-228477 (URN)10.1063/1.4875636 (DOI)000336919400017 ()
Projects
EU GRINDOOR
Funder
EU, FP7, Seventh Framework Programme, 267234
Available from: 2014-07-15 Created: 2014-07-15 Last updated: 2017-12-05Bibliographically approved
Kaewmaraya, T., Ramzan, M., Osorio-Guillen, J. M. & Ahuja, R. (2014). Electronic structure and ionic diffusion of green battery cathode material: Mg2Mo6S8. Solid State Ionics, 261, 17-20
Open this publication in new window or tab >>Electronic structure and ionic diffusion of green battery cathode material: Mg2Mo6S8
2014 (English)In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 261, p. 17-20Article in journal (Refereed) Published
Abstract [en]

We report ab-initio density functional theory calculations of crystal and electronic structure of Mg2Mo6S8, a candidate material to be used in rechargeable magnesium batteries, by employing hybrid exchange-correlation functionals. We find that Mg2Mo6S8 crystalizes in a triclinic geometry and it is a semiconductor with an indirect band gap. Ab-initio molecular dynamics shows that Mg ions present progressive diffusion starting at 200 K with a preferable path through the channel between Mo6S8 blocks along the [010] direction. The intercalation voltage of the system is also determined and the results show that the voltage evaluated by PBE and hybrid functionals likely implies the lower and the upper limit of the experimental value. Lastly, we confirm the dynamical stability of the crystal structure by the calculated phonon dispersion relation. 

Keywords
Mg-ion batteries, First-principle calculations, Hybrid functionals, Molecular dynamics
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-229710 (URN)10.1016/j.ssi.2014.03.023 (DOI)000338819500004 ()
Available from: 2014-08-18 Created: 2014-08-12 Last updated: 2017-12-05Bibliographically approved
Århammar, C., Endrino, J. L., Ramzan, M., Horwat, D., Blomqvist, A., Rubensson, J.-E., . . . Ahuja, R. (2014). Probing temperature-induced ordering in supersaturated Ti-1 (-) xAlxN coatings by electronic structure. Surface & Coatings Technology, 242, 207-213
Open this publication in new window or tab >>Probing temperature-induced ordering in supersaturated Ti-1 (-) xAlxN coatings by electronic structure
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2014 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 242, p. 207-213Article in journal (Refereed) Published
Abstract [en]

The ordering of supersaturated cubic titanium aluminum nitride (c-Ti0.35Al0.65N) coatings is probed from room temperature up to and above the point of spinodal decomposition, using Near Edge X-ray Absorption Fine-structure (NEXAFS) and first principles calculations. The measured and calculated nitrogen (N) K spectra suggest that unoccupied N p states hybridize with Ti d states. When temperature is raised the N p-Ti d overlap decreases, whereas hybridization between N p and Al p tends to increase. The observed spectral changes with temperature together with calculations of defect heat of formation suggest a depletion of N in the surroundings of Ti in c-Ai(1) (-) xAlxN and/or in the formed c-TiN.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-204951 (URN)10.1016/j.surfcoat.2013.10.054 (DOI)000333782400030 ()
Available from: 2013-08-13 Created: 2013-08-13 Last updated: 2017-12-06Bibliographically approved
Sagynbaeva, M., Panigrahi, P., Yunguo, L., Ramzan, M. & Ahuja, R. (2014). Tweaking the magnetism of MoS2 nanoribbon with hydrogen and carbon passivation. Nanotechnology, 25(16), 165703
Open this publication in new window or tab >>Tweaking the magnetism of MoS2 nanoribbon with hydrogen and carbon passivation
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2014 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 25, no 16, p. 165703-Article in journal (Refereed) Published
Abstract [en]

Using density functional theory (DFT), we report the modulated electronic and magnetic properties of MoS2 nanoribbon by passivating the ribbon edges with H and C separately. For the modeled symmetric MoS2 nanoribbon with a zig-zag type edge, one side is terminated at Mo and the other side is terminated at S. For the zig-zag type, we have studied two ribbons of width similar to 3 angstrom and 6 angstrom respectively. Both of these pristine zig-zag type nanoribbons are found to be metallic and also ferromagnetic. However, the increase in the ribbon width results in a decrease in the net magnetic moment of the nanoribbon. Thereafter, we study the modulated electronic and magnetic properties of the nanoribbon of similar to 3 angstrom width by saturating the ribbon edges with H and C. In one case, by passivating the zig-zag type ribbon with H at the S terminated edge, we find a net increase in magnetic moment of the ribbon when compared with the pristine one. Furthermore, when the ribbon is passivated with H at both of the edges, the net magnetic moment shows a decreasing trend. In another case, the zig-zag nanoribbon is passivated with C in a similar fashion to H and we find with one edge passivation the net magnetic moment of the ribbon decreases, whereas with both edges C passivated the ribbon magnetism increases significantly. However, the nanoribbon modeled with the armchair type of edge and terminated with Mo at both sides is found to be non-magnetic and semiconducting. Passivating the armchair type nanoribbon with H and C, we find the band gap shows an increasing trend when going from one side to both sides passivation. In all cases, the armchair type nanoribbons show non-magnetic behavior.

Keywords
MoS2 nanoribbon, magnetic, semiconducting
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-224566 (URN)10.1088/0957-4484/25/16/165703 (DOI)000333814700011 ()
Available from: 2014-05-19 Created: 2014-05-14 Last updated: 2017-12-05Bibliographically approved
Belonoshko, A. B., Ramzan, M., Mao, H.-k. & Ahuja, R. (2013). Atomic Diffusion in Solid Molecular Hydrogen. Scientific Reports, 3, 2340
Open this publication in new window or tab >>Atomic Diffusion in Solid Molecular Hydrogen
2013 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, p. 2340-Article in journal (Refereed) Published
Abstract [en]

We performed ab initio molecular dynamics simulations of the C2c and Cmca-12 phases of hydrogen at pressures from 210 to 350 GPa. These phases were predicted to be stable at 0 K and pressures above 200 GPa. However, systematic studies of temperature impact on properties of these phases have not been performed so far. Filling this gap, we observed that on temperature increase diffusion sets in the Cmca-12 phase, being absent in C2c. We explored the mechanism of diffusion and computed melting curve of hydrogen at extreme pressures. The results suggest that the recent experiments claiming conductive hydrogen at the pressure around 260 GPa and ambient temperature might be explained by the diffusion. The diffusion might also be the reason for the difference in Raman spectra obtained in recent experiments.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-204936 (URN)10.1038/srep02340 (DOI)000322565300003 ()
Available from: 2013-08-13 Created: 2013-08-13 Last updated: 2017-12-06Bibliographically approved
Kaewmaraya, T., Ramzan, M., Sun, W., Sagynbaeva, M. & Ahuja, R. (2013). Atomistic study of promising catalyst and electrode material for memory capacitors: Platinum Oxides. Computational materials science, 79, 804-810
Open this publication in new window or tab >>Atomistic study of promising catalyst and electrode material for memory capacitors: Platinum Oxides
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2013 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 79, p. 804-810Article in journal (Refereed) Published
Abstract [en]

Platinum oxides have the technological importance as evidenced by numerous studies concentrating on their crystal structures to attain the clear atomistic understanding but the controversy exists between the experimental and theoretical studies. In our present study, we report the electronic and optical properties of crystalline PtO and PtO2 on the basis of Heyd-Scuseria-Ernzerhof (HSE06) functional within the framework of the density functional theory (DFT). We present the structural parameters, electronic and optical properties of several proposed structures of PtO and PtO2. We find that PtS-type structure of PtO and CaCl2-type structure of PtO2 are the most stable structures of these materials on the basis of hybrid functional and they appear to be semiconductors with band gap values of 0.87 eV and 1.85 eV, respectively. The mechanical stability of these structures is also confirmed by calculating the phonon band structures. The corresponding structural parameters are found in good agreement with experimental values. Furthermore, we present the bader charge analysis and optical properties of these phases. 

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-204962 (URN)10.1016/j.commatsci.2013.07.021 (DOI)000324471100102 ()
Available from: 2013-08-13 Created: 2013-08-13 Last updated: 2017-12-06Bibliographically approved
Ramzan, M., Li, Y., Chimata, R. & Ahuja, R. (2013). Electronic, mechanical and optical properties of Y2O3 with hybrid density functional (HSE06). Computational materials science, 71, 19-24
Open this publication in new window or tab >>Electronic, mechanical and optical properties of Y2O3 with hybrid density functional (HSE06)
2013 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 71, p. 19-24Article in journal (Refereed) Published
Abstract [en]

In this paper, we have investigated the electronic, optical and mechanical properties of the Y2O3 crystal by first-principle calculations based on the density-functional theory. The generalized gradient approximation (GGA-PBE) and hybrid exchange-correlation functional (HSE06) are both used for comparative study. It is found that, the band gap of Y2O3 calculated by HSE06 method (6.0 eV) is in good agreement with the experimental band gap data (5.5 eV), and HSE06 gives better electronic structure description close to experiments. Then we calculate the elastic constants, and derive the corresponding properties i.e.; bulk, shear and Young's moduli, and Poisson's ratio. Our calculated elastic and mechanical properties correspond well with experimental data. Besides, we also obtain the equilibrium lattice and bulk modulus of yttria by fitting the Birch-Murnaghan equation of state. It is found that, the HSE06 well reproduce the experimental lattice parameters, equilibrium volume and bulk modulus of Y2O3. Based on the accurate described crystal and electronic structure and mechanical properties by HSE06 method, the optical properties of this material are also analyzed.

Keywords
Hybrid density functional, Electronic structure, Mechanical properties, Optical properties
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-198896 (URN)10.1016/j.commatsci.2012.12.026 (DOI)000316661300003 ()
Available from: 2013-05-02 Created: 2013-04-29 Last updated: 2017-12-06Bibliographically approved
Ramzan, M., Li, Y. & Ahuja, R. (2013). Electronic structure, mechanical and optical properties of In2O3 with hybrid density functional (HSE06). Solid State Communications, 172, 37-40
Open this publication in new window or tab >>Electronic structure, mechanical and optical properties of In2O3 with hybrid density functional (HSE06)
2013 (English)In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 172, p. 37-40Article in journal (Refereed) Published
Abstract [en]

In this study, the hybrid densily correlation functional (HSE06) is used to explore the eleclronic structure and optical properties of In2O3, on the basis of density functional theory (DFT). The calculated equilibrium lattice parameters, volume and bulk modulus of this compound, are comparable with the experimental results available in the literature. The bandgap of In2O3 has been a matter of debate in literatures. However, our calculated bandgap can bridge the gap between experiment and theory, and is in good agreement with the available experimental results. Furthermore, we calculate and analyze the optical and mechanical properties of this compound. We hope that our work will help to understand the correct electronic structure and optical properties of this compound.

Keywords
Hybrid density functional, Electronic structure, Mechanical properties, Optical properties
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-221700 (URN)10.1016/j.ssc.2013.08.020 (DOI)000332019600009 ()
Available from: 2014-04-03 Created: 2014-04-03 Last updated: 2017-12-05Bibliographically approved
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