Ing. Oldřich Schneeweiss, DrSc.
Multiscale Modelling and Measurements of Physical Properties (CEITEC IPM), Electrical and Magnetic Properties Group
315, Mössbauer.lab., 120
+420 532 290 434, +420 532 290 311, +420 532 290 312
Iron and iron oxide nanoparticles with applications in the magnetic separation processes
Research center of powdered nanomaterials
Structure, electrical and magnetic properties of nanocrystalline materials composed of carbon and 3d transition metals
Atomic ordering at surfaces and interfaces of alloys of 3d metals
Surfaces and interfaces in structural materials - applications of modern technologies and computer modelling
H. Elhadidy, F. Z. Mahi, J. Franc, A. Musiienko, V. Dedic, O. Schneeweiss,
High frequency noise calculation in Schottky metal-semiconductor-metal
structure and parameter retrieval of nanometric CdTe structure
Thin Solid Films 645 (2018)340
An analytical model to calculate the noise spectral density in Metal-Semiconductor-Metal (M-S-M) structure of Schottky contacts has been developed. The model based on the linearization of Langevin approach of carrier motion inside a bulk semiconductor, and taking into account the fluctuations in the leakage current through the structure due to the barrier lowering by the image force effect. Particularly, the calculations describe two quantities of noise: electric field and total current spectral densities. The results obtained from the Au-CdTe-Au Schottky structure exhibit sharp resonances due to the effect of plasma frequency oscillations and the relative thickness of the depletion region below the anode. Moreover, the noise current spectrum exhibits Lorentzian behavior when the M-S-M has the form of a homogenous structure (thickness of depletion region ≈ 0). These results are in agreement with that reported by Monte Carlo technique of metal Schottky structure. The discussion of the noise spectra as a function of structure parameters revealed that the nanometric M-S-M structures with undoped CdTe can be used as Schottky detectors/emitters in Terahertz frequency applications.
Oldřich Schneeweiss, Martin Friák, Marie Dudová, David Holec, Mojmír Šob, Dominik Kriegner, Václav Holý, Přemysl Beran, Easo P. George, Jörg Neugebauer, and Antonín Dlouhý,
Magnetic properties of the CrMnFeCoNi high-entropy alloy,
Physical Review B 96 (2017) 014437-1 - 014437-13.
We present experimental data showing that the equiatomic CrMnFeCoNi high-entropy alloy undergoes two magnetic transformations at temperatures below 100 K while maintaining its fcc structure down to 3 K. The first transition, paramagnetic to spin glass, was detected at 93 K and the second transition of the ferromagnetic type occurred at 38 K. Field-assisted cooling below 38 K resulted in a systematic vertical shift of the hysteresis curves. Strength and direction of the associated magnetization bias was proportional to the strength and direction of the cooling field and shows a linear dependence with a slope of 0.006 +/- 0.001 emu/T. The local magnetic moments of individual atoms in the CrMnFeCoNi quinary fcc random solid solution were investigated by ab initio (electronic density functional theory) calculations. Results of the numerical analysis suggest that, irrespective of the initial configuration of local magnetic moments, the magnetic moments associated with Cr atoms align antiferromagnetically with respect to a cumulative magnetic moment of their first coordination shell. The ab initio calculations further showed that the magnetic moments of Fe and Mn atoms remain strong (between 1.5 and 2 Bohr magneton), while the local moments of Ni atoms effectively vanish. These results indicate that interactions of Mn- and/or Fe-located moments with the surrounding magnetic structure account for the observed macroscopic magnetization bias.
O. Schneeweiss, B. David, T. Žák, J. Filip, J. Tuček, R. Zbořil:
Magnetic interactions between nanoparticles formed during calcination of ferrihydrite,
Acta Physica Polonica A 118 (2010) 749-750
O. Schneeweiss, B. David, T. Žák, R. Zbořil, and M. Mashlan:
Nanocrystalline Fe–Ni and Fe–Co samples prepared by powder processing
J. Magn. Magn. Mater., 310 (2007) e858–e860
B. David, M. Pizúrová, O. Schneeweiss, P. Bezdička, M. Klementová, J. Filip, R. Alexandrescu, F. Dumitrache, C.T. Fleaca, I. Voicu, and I. Morjan:
Multi-walled carbon nanotubes formed by condensed-phase conversions of Fe-C-based nanopowder in vacuum
Czech. J. Phys. 56 2006 E51-E61
B. David, O. Schneeweiss, N. Pizúrová, M. Klementová, P. Bezdička, R. Alexandrescu, F. Dumitrache, and I. Morjan:
Fe3C nanopowder synthesized by laser pyrolysis and its annealing behaviour
Surf. Interf. Analysis 38, 2006 482-485
J. Čermák, I. Stloukal and O. Schneeweiss: Short-Circuit Diffusion of 99Mo in Partly Crystallized Fe76Mo8B15Cu1, Fe40Ni40B20 and Fe80B20 Alloys. Proceedings NANO '05, Brno, Czech Republic, November 8-10, 2005, p. 302.
B. David, M. Pizúrová, O. Schneeweiss, P. Bezdička, R. Alexandrescu, I. Morjan, A. Crunteanu, and I. Voicu:
Magnetic properties of iron/graphite core-shell nanoparticles prepared by annealing of Fe-G-N-based nanocomposite
J. Magn. Magn. Mater. 290 (2005) 179-182
B. David, M. Pizúrová, O. Schneeweiss, P. Bezdička, I. Morjan, and R. Alexandrescu:
Preparation of iron/graphite core-shell structured nanoparticles
J. Alloys Compd. 378 (2004) 112-116
O. Schneeweiss, Y. Jirásková, T. Žák, J. Šebek, S.F. Lin, and X.K. Yao:
Preparation and properties of FeNi-Mg/MgO nanocomposite
Czech. J. Phys. 52 (2002) 167–170
O. Schneeweiss, Y. Jirásková, J. Čermák and P. Lejček: Atomic Ordering at Grain Boundaries in Fe-Si and Fe-Al Alloys. Proceedings of International Conference on the Applications of the Mössbauer Effect (ICAME2001), Kluwer, Dordrecht, 2002, 571.
Y. Jirásková, M. Svoboda, O. Schneeweiss, and T. Žák:
Structural properties of austenitic stainless steel in the initial state and after rf plasma nitriding
Czech. J. Phys. 52 (2002) A61–A64
O. Schneeweiss, Y. Jirásková, J. Čermák and P. Lejček: Comparison of Site Preferences of 57Co at Grain Boundaries in Fe-Si and Fe-Al Alloys. METAL 2001 - 10th International Metallurgical & Material Conference, Ostrava, Czech Republic, May 15-17 2001, CD-ROM.