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22 results on '"Barnasas, Alexandros"'

3. ZnO Matrices as a Platform for Tunable Localized Surface Plasmon Resonances of Silver Nanoparticles

Author

Ntemogiannis, Dimitrios, primary, Tsarmpopoulou, Maria, additional, Stamatelatos, Alkeos, additional, Grammatikopoulos, Spyridon, additional, Karoutsos, Vagelis, additional, Anyfantis, Dimitrios I., additional, Barnasas, Alexandros, additional, Alexopoulos, Vasilis, additional, Giantzelidis, Konstantinos, additional, Ndoj, Emanuel A., additional, Sigalas, Mihail, additional, and Poulopoulos, Panagiotis, additional

Published
2024
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7. Growth, Magnetic Anisotropies and Exchange Bias of Thin Ni0.95Fe0.05/NiFeO Multilayers

Author

Anyfantis, Dimitrios I., Ballani, Camillo, Kanistras, Nikos, Barnasas, Alexandros, Kapaklis, Vassilios, Schmidt, Georg, Papaioannou, Evangelos Th, Poulopoulos, Panagiotis, Anyfantis, Dimitrios I., Ballani, Camillo, Kanistras, Nikos, Barnasas, Alexandros, Kapaklis, Vassilios, Schmidt, Georg, Papaioannou, Evangelos Th, and Poulopoulos, Panagiotis

Abstract

Ni0.95Fe0.05/NiFeO multilayers were fabricated by radio frequency magnetron sputtering and natural oxidation. Doping of Ni by only 5 at. % Fe results in enhanced layering quality as X-ray reflectivity reveals. Due to magnetostatic anisotropy, the multilayers were found to be in-plane magnetized. The influence of mild thermal annealing (T = 525 K) on the magnetic properties of NiFe/NiFeO multilayers is also investigated. Annealing results in the enhancement of perpendicular magnetic anisotropy, mainly due to an increase in the uniaxial volume anisotropy term. Temperature-dependent hysteresis measurements between 4-400 K revealed considerable enhancement of coercivity and appearance of exchange bias effect.

Published
2022
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9. Quantum Confinement Effects of Thin Co3O4 Films

Author

Barnasas, Alexandros, primary, Garoufalis, Christos S., additional, Anyfantis, Dimitrios I., additional, Bouropoulos, Nikolaos, additional, Poulopoulos, Panagiotis, additional, Hayrapetyan, David B., additional, and Baskoutas, Sotirios, additional

Published
2021
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14. Magnetic Aspects and Large Exchange Bias of Ni0.9Co0.1/NiCoO Multilayers

Author

Anyfantis, Dimitrios I., Kanistras, Nikos, Ballani, Camillo, Barnasas, Alexandros, Kapaklis, Vassilios, Schmidt, Georg, Papaioannou, Evangelos Th., Poulopoulos, Panagiotis, Anyfantis, Dimitrios I., Kanistras, Nikos, Ballani, Camillo, Barnasas, Alexandros, Kapaklis, Vassilios, Schmidt, Georg, Papaioannou, Evangelos Th., and Poulopoulos, Panagiotis

Abstract

Ultrathin films of Ni-0.Co-9(0).(1) were grown by radio frequency magnetron sputtering. By means of a periodic natural oxidation procedure they were transformed into Ni-0.Co-9(0).(1)/NiCoO multilayers. Room temperature hysteresis loops recorded via the magneto-optic Kerr effect have revealed over all in-plane magnetic anisotropy due to magnetostatic anisotropy. Mild thermal annealing at 250 degrees C enhanced a tendency for perpendicular magnetic anisotropy, mainly due to an increase of the uniaxial volume anisotropy term. Spin reorientation transition, exchange bias larger than 700 Oe, and strong coercivity enhancement were observed via a superconducting quantum interference device at low temperatures after field cooling.

Published
2021
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17. Growth, Magnetic Anisotropies and Exchange Bias of Thin Ni 0.95 Fe 0.05 /NiFeO Multilayers.

Author

Anyfantis, Dimitrios I., Ballani, Camillo, Kanistras, Nikos, Barnasas, Alexandros, Kapaklis, Vassilios, Schmidt, Georg, Papaioannou, Evangelos Th., and Poulopoulos, Panagiotis

Subjects
MAGNETIC anisotropy, PERPENDICULAR magnetic anisotropy, MULTILAYERS, RADIO frequency, MAGNETIC properties
Abstract

Ni0.95Fe0.05/NiFeO multilayers were fabricated by radio frequency magnetron sputtering and natural oxidation. Doping of Ni by only 5 at. % Fe results in enhanced layering quality as X-ray reflectivity reveals. Due to magnetostatic anisotropy, the multilayers were found to be in-plane magnetized. The influence of mild thermal annealing (T = 525 K) on the magnetic properties of NiFe/NiFeO multilayers is also investigated. Annealing results in the enhancement of perpendicular magnetic anisotropy, mainly due to an increase in the uniaxial volume anisotropy term. Temperature-dependent hysteresis measurements between 4–400 K revealed considerable enhancement of coercivity and appearance of exchange bias effect. [ABSTRACT FROM AUTHOR]

Published
2022
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18. Growth and Optical Properties of MoO3 thin Films

Author

Barnasas, Alexandros, Diamantopoulos, Nikolaos C., Anyfantis, Dimitrios I., Bouropoulos, Nikolaos, Constantin, Politis, and Poulopoulos, Panagiotis

Abstract

Thin Mo films in the thickness range between 1 and 164 nm have been deposited on high-quality quartz and Corning glass substrates by Radio Frequency (RF) magnetron sputtering under high vacuum (base pressure ~ 3 × 10-7 mbar). The sputtering target was metallic Mo. Subsequent short annealing of Mo at temperatures between about 400 °C - 600 °C in a muffle furnace in air produced MoO3 thin films. Heating even to 400°C resulted in significant growth of crystal size. Surprisingly, films thinner than about 50 nm could not be heated at higher temperatures due to the evaporation of the oxide. Ultraviolet – visible light absorption spectroscopy experiments were employed for the determination of the optical band gap. The results for direct and indirect allowed transitions are discussed.

Published
2022
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22. Quantum Confinement Effects of Thin Co 3 O 4 Films.

Author

Barnasas, Alexandros, Garoufalis, Christos S., Anyfantis, Dimitrios I., Bouropoulos, Nikolaos, Poulopoulos, Panagiotis, Hayrapetyan, David B., and Baskoutas, Sotirios

Subjects
QUANTUM confinement effects, EFFECTIVE mass (Physics), LIGHT absorption, MAGNETRON sputtering, THIN films
Abstract

Thin Co films were deposited on quartz and Corning glass by radio frequency magnetron sputtering. The films were postannealed at 500 °C in a furnace in air atmosphere. The resulting samples were examined with X-ray diffraction experiments, which revealed that they consist of single-phase, polycrystalline C o 3 O 4 . The morphology of selected samples was recorded by atomic force microscopy. Ultraviolet-visible light absorption spectroscopy experiments probed the absorbance of the films in the wavelength range 200–1100 nm. Two types of transitions (energy gaps) were clearly identified. Both of them were found to be "blue shifted" with decreasing film thickness; this is interpreted as evidence of quantum confinement effects. For the case of the first gap value, this was corroborated by calculations based on a combination of the Potential Morphing Method and the effective mass approximation. [ABSTRACT FROM AUTHOR]

Published
2021
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