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1

Nano-structured (Mo,Ti)C-C-Ni magnetic powder

Kaczmarek S. M., Biedunkiewicz A., Bodziony T., Figiel P., Skibiński T., Krawczyk M., Gabriel-Półrolniczak U.

Journal of Achievements in Materials and Manufacturing Engineering

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2018

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Vol. 86, nr 1

5--13

EN

Purpose: The paper presents the results of phase composition and magnetic properties of Mo-Ni-Ti-C nanostructured powders. The aim of this research is understanding the correlation between key magnetic properties and the parameters that influence them in the nanostructured powders from Mo-Ni-Ti-C system. Design/methodology/approach: The powder samples were synthesised using modified sol-gel method. Obtained powder were subjected for composition and magnetic properties in a wide temperature range by means of Electron Paramagnetic Resonance (EPR) and magnetic susceptibility measurements. To study the phase composition X-ray diffraction were performed. The morphology of the powders were investigated by scanning electron microscopy (SEM). Findings: Different kinds of structural and magnetic phases have been found in the investigated compounds, e.g. (Mo, Ti)C, C, Ni. It was found that such different phases create different kinds of magnetic interactions, from paramagnetic, antiferromagnetic up to superparamagnetic. Significant magnetic anisotropy has been revealed for low temperatures, which lowers with temperature increase. Moreover, non-usual increasing of the magnetization as a function of temperature was observed. It suggests, that overall longrange AFM interaction may be responsible for the magnetic properties. Research limitations/implications: For the future work explanation which phases in Mo-Ni-Ti-C system are responsible for different kinds of magnetic interactions are planned. Practical implications: The composition of different kinds of phases may be controlled to tune magnetic properties of the nanostructured Mo-Ni-Ti-C systems. Originality/value: In this study, for the first time Mo-Ni-Ti-C nanostructured samples were prepared with different kinds of structural and magnetic phases, creating different kinds of magnetic interactions, from paramagnetic, antiferromagnetic up to superparamagnetic-like. The latter seems to be formed due to the presence of magnetic nanoparticles and longrange antiferromagnetic interactions dominating in the whole temperature range.

2

Terahertz range double direction isolator based on stratified antiferromagneticdielectric structures : theoretical investigation

Vytovtov K., Hnatushenko V., Zouhdi S.

Elektronika : konstrukcje, technologie, zastosowania

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2015

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Vol. 56, nr 2

75-78

EN

A double direction isolator based on a stratified antiferromagnetic-dielectric structure is proposed in the paper. Frequency dependence of the reflection coefficient on the incident angle and the anisotropy axis orientation is investigated analytically as the key feature of the isolator. Instead of well-known Faraday effect, we use strongly nonlinear frequency dispersion of the structure response to achieve desired non-reciprocal performance. It is shown that proposed isolator provides directional isolation of the incident plane wave at two frequencies of 0.55 THz and 1.65 THz with the half-power level bandwidths of 0.16 THz and 0.22 THz, respectively. Tuning of the isolator operating frequencies is the second issue solved in the paper. Frequency tuning is realized by a changing of external magnetic field. Both fine and broadband frequency tuning are demonstrated.

PL

Dwukierunkowy izolator pracujący w paśmie terahercowym, wykorzystujący antyferromagnetyczne, warstwowe struktury dielektryczne, przedstawiony jest w artykule. Charakterystyka częstotliwościowa współczynnika odbicia w zależności od kąta padania fali i orientacji osi anizotropii została przeanalizowana jako podstawowy parametr izolatora. Zamiast dobrze znanego efektu Faradaya wykorzystano fakt silnego rozproszenia częstotliwości odpowiedzi do analizy zachowania struktury izolatora. Wykazano, że proponowany izolator zapewnia izolację kierunkową dla dwóch częstotliwości 0,55 THz i 1,65 THz przy szerokości pasma 0,16 THz i 0,22 THz odpowiadającej mocy połówkowej. Przestrajanie częstotliwości pracy izolatora jest drugim zagadnieniem analizowanym w tej pracy. Przestrajanie częstotliwości pracy realizowane jest za pomocą zewnętrznego pola magnetycznego. Przedstawione zostały charakterystyki przestrajania izolatora.

3

Investigation of the reflective properties of layered antiferromagnetic-dielectric structures

Vytovtov K., Arkhipov A., Gnatushenko V.

Elektronika : konstrukcje, technologie, zastosowania

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2014

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Vol. 55, nr 2

55-58

EN

Reflection properties of layered antiferromagnetic-dielectric structures with an oblique axis orientation and an oblique planar wave falling are investigated in this paper. Nonreciprocal angle dependence in oblique axis orientation was obtained and described. Founded properties are based not on the Faraday effect but on the non-reciprocity of anisotropic material - FeF2 antiferromagnetic. Obtained result were studied in terahertz region but may be used in near-infrared region and radio frequency region with another anisotropic materials using. Obtained results allow us to propose a valve based on the investigated structure.

PL

Właściwości odbijające warstwowych antyferromagnetyczno-dielektrycznych struktur z ukośną orientacją osi i ukośną, płaską falą padania są badane w tej pracy. Uzyskano i opisano zależność kąta w orientacji skośnej osi. Założone właściwości nie są oparte na efekcie Faradaya, ale na braku wzajemności materiału anizotropowego-antyferromagnetycznego FeF2. Otrzymany wynik oceniano w obszarze terahercowym ale może być stosowany w obszarze bliskiej podczerwieni i w obszarze częstotliwości radiowych w odniesieniu do innych materiałów anizotropowych.

4

Wpływ substytucji kationowej na strukturalne i magnetyczne właściwości wybranych chromitów selenowych

Jendrzejewska I.

Wiadomości Chemiczne

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2010

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[Z] 64, 9-10

859-898

EN

Selenospinels with general formula ACr2Se4 (A = Zn, Cu, Cd) were doped with nickel and tin ions. The chemical synthesis was carried out based on solid phase reactions. To estimate the chemical composition of the mono- and polycrystalline compounds, the following methods were applied: JEOL scanning microscope and ICP-AES (Inductively Coupled Plasma - Atomic Emission Spectrometry). For the obtained polycrystalline compounds, their structural parameters were defined using X-ray diffraction analysis and Rietveld method. Definition of structure of the monocrystals was carried out using KM4 four-circle diffractometer and SHELX software. Magnetic properties were investigated with strong stationary magnetic fields up to 14 T in the temperature range of 4.2-300 K using an induction magnetometer and with stationary magnetic fields up to 0.5 T in the temperature range of 1.8-300 K using a SQUID superconducting magnetometer. In the systems doped with nickel, depending on the reaction stoichiometry, nickel ions were directed to tetrahedral or octahedral positions. When the octahedral positions are fully occupied by chromium ions, small amounts of nickel directed to tetrahedral positions are able to occupy them. The increasing amount of Ni2- ions tends to occupy the octahedral positions in accordance with preference energy, leading to change in structure from cubic to monoclinic one [19, 37, 38]. Nickel ions present in the spinel crystal lattice influence the magnetic properties of these compounds. For ZnCr2-xNixSe4 system, an increase in values of effective magnetic moment and saturation magnetic moment accompanying the increase in nickel ions concentration was ascertained. It was caused by the presence of another magnetic ions in ZnCr2Se4 crystal lattice. The values of paramagnetic Curie-Weiss point and Néel point decrease with the increase in nickel concentration. It is associated with an increase in antiferromagnetic interactions in the system caused by nickel ions [39-41]. Like in the Cd1–xNixCr2Se4system, saturation magnetic moment does not depend on the amount of nickel built-in, and the crystals exhibit strong ferromagnetic interactions. Lack of a change in saturation indicates that nickel is built in with compensated magnetic moment, or in a low-spin state (S = 0). Cadmium and nickel ions occupy tetrahedral positions and chromium ions - octahedral ones [42]. In the systems doped with tin, the reactions carried out in the solid phase were aimed to build in tin ions in tetra-and octahedral positions. X-ray diffraction studies confirmed the presence of tin ions in selected chromites. Mössbauer spectroscopy applied for the complex system Zn1–xSnxCr2Se4 confirmed the presence of tin ions in two inequivalent positions: in tetrahedral and in octahedral environments. Based on theses considerations, the general formula of these compounds may be as follows: ZnxSnδCrySnηSe4, where δ – parameter describing the share of tin ions in tetrahedral sublattice, η – parameter describing the share of tin ions in octahedral sublattice [43]. Although tin ions does not contribute to a magnetic share, their presence in the crystal lattice promotes an increase in antiferromagnetic interactions in the studied compounds. Under the influence of tin ions, conductance changes from p-type (hole conduction) occurring in pure ZnCr2Se4to n-type (electron conduction) [44, 45]. In CuCr2-xSnxSe4 system, magnetic properties change from ferromagnetic for nominal value x = 0.2 to antiferromagnetic for nominal value x = 1.0. These changes are caused by the presence of Sn4+ ions in the system, generating Cr2+ ions. The observed change in structure is caused by Jahn-Teller effect, occurring in the presence of Cu2+ and Cr2+ ions [46].

5

Inhomogeneous superconductivity and vortices in the stripe states

Lenkowska-Czerwińska T.

Journal of Technical Physics

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2002

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Vol. 43, no 3

335-341

EN

Spatially inhomogeneous features in the spin and charge structures have been indicated in the number of experiments on high temperature materials e.g. La2-xSrxCuO4. The simple realization of this state is striped domain wall where charges form a nanoscale linear pattern in an antiferromagnetically ordered isolator. These represent a nanoscale distribution of charge and spin that is believed to be commensurably locked by the tilt distortions of the lattice. The phenomenological model of charge and spin inhomogeneities in the stripe phase of superconducting cuprates on the ground of Ginzburg-Landau theory is proposed. The corresponding free energy for the coupled charge and spin-density wave, and superconducting order parameters is constructed. The phase diagram for inhomogeneous superconducting state is discussed. The effective coherence length and the penetration depth in the London limit are introduced. The critical magnetic fields and the energy of the isolated vortex line are obtained.