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Featured researches published by T. Žák.


Sensors and Actuators A-physical | 1997

Structure sensitivity of magnetic and electrical properties of FeAl intermetallic compounds

M. Vondráček; O. Schneeweiss; T. Žák

Abstract We have investigated the structure dependence of the electrical and magnetic properties of FeAl compounds with 28 at.% Al. Local structure changes and hyperfine field parameters have been studied using Mossbauer spectroscopy. The magnetic properties and magnetoresistance exhibit strong dependence on the degree of plastic deformation. Additional alloying, e.g. by chromium, also changes the properties investigated. The results show that electrical, magnetic, and mechanical properties can be changed by controlled heat and mechanical treatment.


Journal of Magnetism and Magnetic Materials | 2000

Fe3Si surface coating on SiFe steel

O. Schneeweiss; Naděžda Pizúrová; Y. Jirásková; T. Žák; B. Cornut

Abstract Fe3Si layers were prepared using chemical vapor deposition of Si on the surface of GO steel and its subsequent heat treatment. The changes in the structure and phase composition after different heat treatment conditions have been analyzed. The coating is characterized by high hardness, good corrosion resistance, high electrical resistivity, and the spin texture which differs from the steel substrate.


Journal of Magnetism and Magnetic Materials | 1993

Magnetoresistance in ordered and disordered Fe72Al28 alloy

O. Schneeweiss; T. Žák; M. Vondráček

Abstract On the Fe-Al alloy near the Fe 3 Al stoichiometry the magnetoresistance and hysteresis loops were measured in the ordered and disordered states. Atomic order and structure were checked by Mossbauer spetroscopy and TEM. The disordered sample shows a usual behaviour of bulk ferromagnetics. The ordered one exhibits large decrease one exhibits large decrease of reisistivity in the magnetic field and lower ability to reach the saturation. The large magnetoresistance effect is explained on the basis of similarity between naturally layered Fe 3 Al structure and artificial multilayers taking into account probable perturbation of spin orientation on the sublattices occupied by the iron atoms with lower magnetic moments.


Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science | 2012

Nanocrystal Growth in Thermally Treated Fe75Ni2Si8B13C2 Amorphous Alloy

Dragica M. Minić; Vladimir A. Blagojević; Dušan M. Minić; Bohumil David; Naděžda Pizúrová; T. Žák

Thermal treatment of amorphous Fe75Ni2Si8B13C2 alloy leads to crystallization of the stable α-Fe(Si) and Fe2B as well as to the metastable Fe3B phase. The study of the mechanism of crystal growth of the α-Fe(Si) phase revealed that the mechanism of α-Fe(Si) growth changes from two dimensional in the early stage to one dimensional in the later stage of crystallization. The Fe2B phase was found to crystallize through two independent routes: from the amorphous phase and from the metastable Fe3B phase, which leads to a different mechanism of crystal growth for each route. Both routes exhibit a change in the mechanism of crystal growth: from two dimensional to one dimensional and from three dimensional to two dimensional, respectively. The respective mechanisms of crystal growth correlate well with the observed changes in preferential orientation of the crystallites of the Fe2B phase.


Czechoslovak Journal of Physics | 1997

Mössbauer and magnetic study of mechanical alloying of Fe3Si

T. Žák; S. Havlíček; O. Schneeweiss; M. Vondráček; N. Števulová

Using Mössbauer spectroscopy and measurement of hysteresis loops and thermomagnetic curves, phase composition and magnetic parameters of Fe3Si mechanically alloyed powders were studied in dependence on milling time and subsequent heat treatment at a thermomagnetic experiment. Samples of as-prepared powders show high value of coercivity, the saturation magnetization and the content of amorphous Fe3Si phase raise with increasing time of milling, the content of α-Fe diminishes. Heat treatment of samples with long enough milling time can produce almost perfect Fe3Si alloy.


Journal of Magnetism and Magnetic Materials | 1996

High temperature magnetization of 3.5% Si steel

T. Žák; Y. Jirásková; O. Schneeweiss; A. Sólyom; P. Marko

Abstract Thermomagnetic curves of rapidly solidified ribbons of Fe-3.5 wt% Si prepared using the single wheel and double roller techniques are discussed in comparison with those of commercial grain oriented transformer sheet samples. It is concluded that the arrangement of defect clusters or silicon or impurity atoms, fixed at the temperature of secondary recrystallization, influence the distribution of magnetic moments at high temperature.


Journal of Magnetism and Magnetic Materials | 1993

Influence of an external magnetic field on the recovery of high strained Fe-28 at% Al alloy

T. Žák; Y. Jirásková; O. Schneeweiss

Abstract The influence of an external magnetic field on the recovery process of nanocrystalline specimens prepared by high straining was studied. Hysteresis loops, coercivity measurements and Mossbauer spectra were taken on samples annealed with the external field on and off. The results show that the field accelerates the recovery process, but only a slight influence on macroscopic magnetic parameters can be observed. In that case, the influence of ordering and magnetic transition effects prevailed.


Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science | 2016

Thermally Induced Structural Transformations of Fe40Ni40P14B6 Amorphous Alloy

Milica Vasić; Pavla Roupcová; Naděžda Pizúrová; Sanja I. Stevanović; Vladimir A. Blagojević; T. Žák; Dragica M. Minić

Thermal stability and thermally induced structural transformations of Fe40Ni40P14B6 amorphous alloy were examined under non-isothermal and isothermal conditions. Formation of metastable α-(Fe,Ni), and stable γ-(Fe,Ni) and (Fe,Ni)3(P,B) crystalline phases as the main crystallization products was observed, while the presence of small amounts of other crystalline phases like Fe23B6 and Fe2NiB was indicated by electron diffraction in HRTEM. Thermomagnetic curve indicated that Fe content in different crystalline phases is very different, resulting in markedly different Curie temperatures after crystallization. Transmission electron microscopy and atomic force microscopy study suggested multiple-layered platelet-shaped morphology, both on the surface and in the bulk of the crystallized alloy sample. The thermal treatment heating rate and maximum temperature affected surface roughness and grain size inhomogeneity.


Journal of Metastable and Nanocrystalline Materials | 2003

Preparation of MgO-(Ni-Fe) Nanocrystalline Composite from Spark Eroded Powder

O. Schneeweiss; Yvonna Jirásková; T. Žák; Petr Bezdička; Eva Večerníková; P. Řepa

Phase analysis of Mg/MgO-(Ni-Fe) powders was carried out usi ng Mössbauer spectroscopy, X-ray diffraction and thermomagnetic (TMG) curve mea sur ments. Changes during annealing were observed by TG/DTA measurements completed wit h gas analysis using mass spectroscopy. X-ray diffraction revealed that MgO dominates in the as-prepared and annealed samples. Mössbauer phase analysis detected original Ni-F e phase, Fe , and small amount of Fe 0 and -Fe. Negligible changes in the phase composition were observed afte r vacuum annealing up to 500 C. At higher temperatures α-Fe and -Fe disappeared and iron content in Ni-Fe has decreased while intensity of Fe 2+ component has increased. Progress in oxidation was detected by TG/DTA above ~512 C.


Czechoslovak Journal of Physics | 2002

Preparation and Properties of FeNi-Mg/MgO Nanocomposite

O. Schneeweiss; Y. Jirásková; T. Žák; J. Šebek; Lin Shaofan; Yao Xinkan

The FeNi-Mg/MgO nanocomposite synthesized by spark erosion of pure Mg and Fe70Ni30 electrodes was investigated by X-ray diffraction, Mössbauer spectroscopy and magnetic measurements. From the X-ray diffraction measurements Mg, MgO, and α-FeNi were recognized. According to the Mössbauer spectra analysis, iron atoms were identified in α-FeNi, Fe1-xO, and FeNi in Mg/MgO phases. The FeNi in Mg/MgO phase consists of fcc γ-FeNi phase which is antiferromagnetic below TN ≈ 40 K and weakly ferromagnetic bcc α-FeNi clusters. The magnetic measurements confirmed the presence of the γ-FeNi phase and the composite model in the form of isolated magnetic particles in Mg/MgO matrix.

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O. Schneeweiss

Academy of Sciences of the Czech Republic

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Naděžda Pizúrová

Academy of Sciences of the Czech Republic

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Bohumil David

Academy of Sciences of the Czech Republic

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Y. Jirásková

Academy of Sciences of the Czech Republic

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Pavla Roupcová

Academy of Sciences of the Czech Republic

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