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NMR in Ferromagnetic Manganites

100%
Novák P.
Acta Physica Polonica A
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2004
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vol. 105
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issue 1-2
57-67
EN
The conditions for observing NMR on the ^{55}Mn nuclei in the ferromagnetic manganites are specified and the information which may be extracted from this NMR are discussed. As examples, the study of the order of the magnetic phase transition and the coexistence of different ferromagnetic phases in the ferromagnetic manganites are presented.
2
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Magnetism and Crystal Field in PrCuAl₃ and NdCuAl₃

64%
Novák P., Diviš M.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
964-966
EN
During the last five years we developed method to calculate crystal field and magnetism of rare-earth ions in solids. The method is fully ab initio with the exception of a single parameter which adjust the position of f states relative to other valence states and it was successfully applied in insulating systems. In this contribution the method is used to explain multiplet splitting and magnetism in PrCuAl₃ and NdCuAl₃ intermetallics. For the Nd compound the agreement between theory and experiment is good, while for the PrCuAl₃ the agreement is less satisfactory which can be due to the more delocalized 4f electrons of Pr³⁺ comparing to Nd³⁺ ion.
3
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Giant Magnetoelectricity in Aluminium Substituted Y-Hexaferrites

51%
Novák P., Chlan V., Knížek K.
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|
issue 5
723-724
EN
The electron structure of Al containing Y-hexaferrite that exhibits the giant magnetoelectricity is calculated. Results show strong preference of Al for octahedral sites. Orbital moment of some of the iron ions is found to be unusually large.
4
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Magnetic Properties of Nanocrystalline Alloys after Electrons Irradiation

51%
Sitek J., Holková D., Dekan J., Novák P.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
708-710
EN
Nanocrystalline (Fe₃Ni₁)₈₁Nb₇B₁₂ alloy was irradiated by electron beams of doses up to 4 MGy. Irradiation had an influence on the magnetic microstructure of the studied alloys. It has manifested as a change in the mean orientation of local magnetization, intensity of the internal magnetic field, and distribution function of induction of internal magnetic field. All these parameters were determined from the measured Mössbauer spectra. The mean orientation of local magnetization was the most sensitive parameter. Structural changes were not identified by the Mössbauer spectroscopy and by X-ray diffraction. The results indicated that the changes of the microscopic magnetic parameters induced by irradiation depend on the phase composition. Intensity of internal magnetic field also contributes to resistivity of alloy against radiation.
5
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Magnetic Circular Dichroism in Electron Microscopy

45%
Rusz J., Novák P., Rubino S., Hébert C., Schattschneider P.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
599-644
EN
Although the analogies between the electron energy loss spectra and X-ray absorption spectra were recognized long ago, the possibility to observe the magnetic circular dichroism in the electron microscope was demonstrated only recently. This technique combines the atom specificity with the high spatial resolution of the transmission electron microscope. Being a very young technique, there are still many open questions concerning the optimization of the signal to noise ratio. In this paper we study the dichroic signal dependence on the sample thickness, acceleration voltage and incoming beam tilt angle of bcc-Fe and fcc-Ni.
6
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Powder Metallurgy Preparation of Co-Based Alloys for Biomedical Applications

39%
Marek I., Novák P., Mlynár J., Vojtěch D., Kubatík T., Málek J.
Acta Physica Polonica A
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2015
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vol. 128
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issue 4
597-601
EN
Co-based alloys represent very important group of materials used for medical applications. Currently, fabrication of these materials is preferentially done by casting or forming. Production by powder metallurgy techniques is less common. However, powder metallurgy fabrication of these alloys brings advantages such as reduced machining, possibility of alloying by high-melting elements, preparation of nanocrystalline materials with enhanced mechanical properties or producing of porous alloys with improved ability to integrate into issues. In this work, our attention was focused on fundamental preparation of an CoCrMo alloy by two methods of powder metallurgy. In the first method, pure metallic powders were mixed, pressed and sintered in vacuum furnace. The second applied technology consisted of mechanical alloying using planetary ball mill and compaction by spark plasma sintering technique. A series of samples was prepared under various conditions by these procedures. Dependence of microstructure, phase composition and mechanical properties of prepared samples on fabrication conditions (milling parameters, sintering temperature etc.) was studied. Obtained results were compared with properties of commercial cast cobalt alloy used for medical applications.
7
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Hyperfine Field in YIG with Charged Substitution

39%
Kohout J., Štĕpánková H., Englich J., Novák P., Kučera M., Nitsch K.
Acta Physica Polonica A
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2000
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vol. 97
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issue 3
519-522
EN
^{57}Fe NMR spectra were measured on thin films of yttrium iron garnet with divalent (Ca^{2+}) and tetravalent (Ge^{4+}) cation substitutions using the spin echo technique at 4.2 K. A series of Y_{3-x}Ca_{x}Fe_{5-x}Ge_{x}O_{12} samples with 0 ≤ x ≤ 0.0 5 was prepared by an epitaxial growth from BaO/B_{2}O_{3}/BaF_{2} flux on gadolinium gallium garnet substrate. Satellite lines corresponding to the iron ions having the Ge^{4+} and Ca^{2+} in their neighbourhood were identified. The sample with the germanium content of x(Ge) = 0.004 and (110) substrate orientation was used for a detailed study: NMR spectra of this sample were measured in an external magnetic field of 0.1 T applied along several directions in the plane of the film. The modification of the isotropic part and the anisotropy tensor of the hyperfine interaction caused by the Ge^{4+} substituent were obtained from the experimental data. The results were compared with those previously reported for trivalent substitution (Ga^{3+}).
8
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Structure and Properties of Fe-Ni-Al-Si Alloys Produced by Powder Metallurgy

39%
Novák P., Mejzlíková L., Hošek V., Martínek M., Marek I., Michalcová A.
Acta Physica Polonica A
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2012
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vol. 122
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issue 3
524-527
EN
Reactive sintering powder metallurgy is a simple alternative to conventional melting and powder metallurgy processes. During this process, pressed powder mixture of pure metals or other precursors is transformed into bulk intermediary phases by thermally activated in situ reaction. This process was previously tested on Fe-Al and Fe-Al-Si alloys. Positive effect of silicon on the reactive sintering behaviour was determined, leading to the development of novel carbon-free high-silicon FeAl20Si20 alloy (given in wt%). In this work, the effect of nickel on the pressureless reactive sintering of Fe-Al-Si pressed powder mixtures was studied. To explain the nickel influence, differential thermal analysis was utilized. Microstructure, phase composition and porosity of the FeAl20Si20Nix (x = 0, 5, 10, 20 wt%) alloys was described. Hardness, wear resistance, high-temperature oxidation resistance and thermal stability were evaluated as functions of nickel content. Results showed that porosity decreases with growing nickel content down to less than 3 vol.%. Oxidation rate of these alloys is more than 10 times lower than that of original FeAl20Si20 alloy. Thermal stability and abrasive wear resistance of these alloys is also superior to Fe-Al and Fe-Al-Si materials.
9
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Effect of Heating Rate on the Formation of Intermetallics during SHS Process

33%
Novák P., Michalcová A., Školáková A., Průša F., Kříž J., Marek I., Kubatík T., Karlík M., Haušild P., Kopeček J.
Acta Physica Polonica A
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2015
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vol. 128
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issue 4
561-563
EN
Self-propagating high-temperature synthesis is a simple and efficient method for the synthesis of various compounds including ceramics and intermetallics. In this process, the compressed mixture of elemental or master alloy powders is ignited or heated to initiate the exothermic reactions leading to the formation of desired compounds. In order to control the process efficiently, the effect of several important parameters has to be determined in each applied alloy system. Previous results showed that those parameters are: initiation temperature, process duration, pressure used for compression and heating rate. This paper is devoted to the description and explanation of the effect of the heating rate on the formation of intermetallics during self-propagating high-temperature synthesis in Fe-Al and Ni-Ti systems. Differential thermal analysis of compressed powder mixtures under various heating conditions and microstructure observation of samples prepared by various heating rates using electric resistance heating and spark plasma sintering were carried out. The effect of heating rates on the formations of intermetallics in studied systems is discussed in this paper.
10
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Distribution of Zn in Magnetoelectric Y-Type Hexaferrite

33%
Kouřil K., Chlan V., Štěpánková H., Telfah A., Novák P., Knížek K., Hiraoka Y., Kimura T.
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issue 5
732-733
EN
We employ ^{67}Zn NMR to study distribution of Zn^{2+} in cationic sites of magnetoelectric Y-type hexaferrite single crystal, Ba_{0.5} Sr_{1.5} Zn_2 Fe_{12} O_{22}. The experimental data are interpreted by comparison with NMR spectra simulated from ab initio calculated hyperfine parameters.
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