Wyniki wyszukiwania - Biblioteka Nauki

1

Structure and some magnetic properties of (BiFeO3) x -(BaTiO3) 1− x solid solutions prepared by solid-state sintering

100%

Kowal K. , Kowalczyk M. , Czekaj D. , Jartych E.

Nukleonika

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2015

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tom 60

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nr 1

81-85

EN

This paper presents the results of the study on structure and magnetic properties of the perovskite-type (BiFeO3)x-(BaTiO3)1−x solid solutions. The samples differing in the chemical composition (x = 0.9, 0.8, and 0.7) were produced according to the conventional solid-state sintering method from the mixture of powders. Moreover, three different variants of the fabrication process differing in the temperatures and soaking time were applied. The results of X-ray diffraction (XRD), Mössbauer spectroscopy (MS), and vibrating sample magnetometry (VSM) were collected and compared for the set of the investigated materials. The structural transformation from rhombohedral to cubic symmetry was observed for the samples with x = 0.7. With increasing of BaTiO3 concentration Mössbauer spectra become broadened reflecting various configurations of atoms around 57Fe probes. Moreover, gradual decreasing of the average hyperfine magnetic field and macroscopic magnetization were observed with x decreasing.

2

Evaluation of Differences between Fe₃O₄ Micro- and Nanoparticles Properties

100%

Duriagina Z. , Tepla T. , Kulyk V.

Acta Physica Polonica A

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2018

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tom 133

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nr 4

869-872

EN

Small sizes of nanoparticles lead to the appearance of new unique functional properties. Under transition to nanosizes in metals and their compounds new specific characteristics appears. In this work, the microstructural and magnetic properties of Fe₃O₄ nanoparticles (Fe₃O₄-NP) have been compared with those of commercially available Fe₃O₄ microparticles (Fe₃O₄-MP) and detailed analysis of differences has been carried out. The synthesis of Fe₃O₄-NP was carried out by means of colloidal method performed without the use of surfactants. Commercial and synthesized particles were characterized using NTEGRA Prima (NT-MDT) atomic force microscope. For magnetic properties investigations we used the method of vibrating sample magnetometer.

3

The low temperature magnetic properties of potassium holmium double tungstate

100%

Borowiec M. , Khatsko E. , Dyakonov V. , Rykova A. , Majchrowski A. , Zayarnyuk T. , Barański M. , Żmija J. , Szymczak H.

Open Physics

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2011

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tom 9

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nr 1

260-262

EN

The magnetic investigations of potassium holmium double tungstate KHo(WO4)2 have been performed. The results of measurements of magnetic susceptibility and magnetization as a function of both temperature (T = 0.5–100 K) and magnetic field (up to 2 T) are presented.

4

Effects of low-level La doping and ageing on TlPb-1223 high T c superconductors

88%

Cigáň A. , Plesch G. , Škrátek M. , Kopčok M. , Maňka J. , Jurdák P. , Koňakovský A.

Open Physics

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2011

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tom 9

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nr 1

213-221

EN

Bulk samples of the nominal composition of (Tl0.6Pb0.5)(Sr0.8Ba0.2)2Ca2Cu3O8+δ−xLaO1.5 (x = 0–0.1) were prepared by using two-step process and their microstructure, T c values, and magnetization were studied. The samples consist of the Tl-1223 dominant phase with small Tl-1212 admixture, which increases with a rise of La content. Five years ageing and following oxygen annealing at 450°C and subsequently at 750°C have only a modest effect on T c values of the studied samples. Low-level La doping (x = 0:04) leads to an increase of T c values by about 2 K in comparison with undoped samples. Oxygen annealing at 750°C results in an increase in the volume magnetization hysteresis in low applied magnetic fields and rise of critical current density at zero magnetic field and 77 K. This effect is most pronounced for the low La doped sample with x = 0.04. Changes of the induced voltage, U originating in the Meissner effect and of its harmonics in dependence on temperature were measured and used for characterization of the temperature distribution of inter-grain junctions.

5

Magnetic Properties of Steel Ball Samples, Investigated before and after Nitriding

88%

Fuks H. , Kaczmarek S. M. , Leniec G. , Michalski J. , Kucharska B. , Wach P.

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6

Magnetic properties of the mixed spin-5/2 and spin-3/2 Blume-Capel Ising system on the two-fold Cayley tree

88%

Yessoufou R. , Amoussa S. , Hontinfinde F.

Open Physics

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2009

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tom 7

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nr 3

555-567

EN

We use exact recursion relations to study the magnetic properties of the half-integer mixed spin-5/2 and spin-3/2 Blume-Capel Ising ferromagnetic system on the two-fold Cayley tree that consists of two sublattices A and B. Two positive crystal-field interactions Δ1 and Δ2 are considered for the sublattice with spin-5/2 and spin-3/2 respectively. For different coordination numbers q of the Cayley tree sites, the phase diagrams of the model are presented with a special emphasis on the case q = 3, since other values of q reproduce similar results. First, the T = 0 phase diagram is illustrated in the (D A = Δ1/J,D B = Δ2/J) plane of reduced crystal-field interactions. This diagram shows triple points and coexistence lines between thermodynamically stable phases. Secondly, the thermal variation of the magnetization belonging to each sublattice for some coordination numbers q are investigated as well as the Helmoltz free energy of the system. First-order and second-order phase transitions are found. The second-order phase transitions become sharper and sharper when D A or D B increases. The first-order transitions only exist for some appropriate non-zero values of D A and/or D B. The corresponding transition lines never connect to the second-order transition lines. Thus, the non-existence of tricritical points remains one of the key features of the present model. The magnetic exponent β 0 of the model is estimated and found to be ¼ at small values of D A = D B = D and β 0 = ½ at large values of D. At intermediate values of D, there is a crossover region where the magnetic exponent displays interesting behaviours.

7

Square Ising Nanowire on the Bethe Lattice

88%

Albayrak E.

Acta Physica Polonica A

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2017

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tom 131

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nr 6

1470-1473

EN

The square-type nanowire is simulated on the Bethe lattice by using the core-shell structure consisting of the Ising spins. A nanoparticle is formed by placing a spin to the center and four others to the corners of a square. Then, each nanoparticle is combined with two neighboring ones with a perfect alignment of the squares to form the nanowire. Only nearest-neighbor spin interactions, either ferromagnetic or antiferromagnetic type, are allowed. The phase diagrams are calculated by studying the thermal variations of magnetizations for various values of bilinear interactions. It is found that the model gives both second- and first-order phase transitions in addition to the tricritical points and compensation temperatures.

8

Analysis of magnetic disturbances of plane caused by permanent magnetization of it's ferromagnetic elements and analysis of magnetic field of chosen class of objects

75%

Wołoszyn M.

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2009

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tom No 60

35-43

9

Elektronowy rezonans paramagnetyczny nanokompozytów (CoFeZr)x(Al2O3)(100-x) wytwarzanych rozpylaniem jonowym

63%

Zhukowski P. , Kołtunowicz T. N. , Sidorenko J. , Fedotova J.

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2012

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tom R. 88, nr 7a

324-326

PL

W pracy przedstawiono wyniki badań metodą elektronowego rezonansu paramagnetycznego (EPR) właściwości magnetycznych nanokompozytów (CoFeZr)x(Al2O3)(100-x) wytworzonych rozpylaniem jonowym w atmosferze argonu (próbki beztlenowe) oraz argonu i tlenu (próbki tlenowe). Ustalono, że w badanych materiałach występuje pojedyncza linia EPR, parametry której Hmin, Hmax, Hg oraz czynnik g wykazują silną zależność kątową. Jest ona związana ze zmianą czynnika rozmagnesowania z kątem ustawienia próbki w stosunku do wektora natężenia pola magnetycznego. Wektor namagnesowania w próbkach beztlenowych jest większy, niż w próbkach tlenowych co jest związane z udziałem części atomów metali w związkach z tlenem. Wygrzewanie termiczne do Ta = 450°C powoduje wzrost wektora namagnesowania i czynnika g.

EN

The paper presents results of studies with the method of electron paramagnetic resonance (EPR) on properties of magnetic nanocomposites (CoFeZr)x(Al2O3)(100-x) produced by ion sputtering in an argon atmosphere (anaerobic samples) or argon and oxygen atmosphere (aerobic samples). It was found that there is a single EPR line in the material studied which parameters like Hmin, Hmax, Hg and a factor g show a strong angular dependence. It is connected with the change of the demagnetization factor according to the sample set angle relative to the vector of magnetic field strength. Magnetization vector in the anaerobic samples is larger than in aerobic samples that is connected with the participation of the certain metal atoms in compounds with oxygen. Thermal annealing up to the value of Ta = 450°C causes increase of the magnetization vector and the factor g.

10

Soret-driven thermohaline convection in dusty ferrofluids saturating a porous medium

63%

Sekar R. , Vaidyanathan G. , Hemalatha R.

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2008

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tom Vol. 13, no 4

1003-1018

EN

The Soret driven thermoconvective instability in multicomponent fluids has wide applications in heat and mass transfer. This paper deals with the theoretical investigation of the effect of dust particles on a Soret-driven ferro thermohaline convection heated and soluted from below subjected to a transverse uniform magnetic field in a porous medium. The Brinkmann model is used. An exact solution is obtained for the case of two free boundaries. Both stationary and oscillatory instabilities are investigated using the linear stability analysis and normal mode technique. It is found that the system stabilizes only through stationary mode. The non-buoyancy magnetization parameter, the dust particle parameter and large values of permeability of the porous medium are found to destabilize the system. The Soret coefficient and the stable solute gradient stabilize the system. The results are presented graphically.

11

Effect of rotation on double-diffusive convection in a magnetized ferrofluid with internal angular momentum saturating a porous medium

63%

Sunil , Mahajan A.

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2008

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tom Vol. 13, no 4

1059-1078

EN

This paper deals with the theoretical investigation of the effect of rotation in a magnetized ferrofluid with internal angular momentum, heated and soluted from below saturating a porous medium and subjected to a transverse uniform magnetic field. For a flat fluid layer contained between two free boundaries, an exact solution is obtained. A linear stability analysis theory and normal mode analysis method have been employed to study the onset of convection. The influence of various parameters on the onset of stationary convection such as rotation, medium permeability, solute gradient, magnetization and internal angular momentum parameters (i.e., coupling parameter, spin diffusion parameter and heat conduction parameter) has been analyzed. The critical magnetic thermal Rayleigh number for the onset of instability is also determined numerically for sufficiently large values of buoyancy magnetization parameter and results are depicted graphically. The principle of exchange of stabilities is found to hold true for the ferrofluid with internal angular momentum saturating a porous medium heated from below in the absence of rotation, coupling between vorticity and spin, microinertia and solute gradient. The oscillatory modes are introduced due to the presence of the rotation, coupling between vorticity and spin, microinertia and solute gradient, which were non-existent in their absence. In this paper, an attempt is also made to obtain the sufficient conditions for the non-existence of overstability.

12

Thermoconvective magnetized ferrofluid with internal angular momentum: a nonlinear stability analysis

63%

Sunil , Mahajan A.

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2011

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tom Vol. 16, no 2

557-580

EN

The generalized energy method is developed to study the nonlinear stability analysis for a magnetized ferrofluid layer heated from below with intrinsic rotation of the particles, in the stress-free boundary case. The mathematical emphasis is on how to control the nonlinear terms caused by the magnetic body force, inertia forces and body couple on a fluid element. By introducing a suitable generalized energy functional, we perform a nonlinear energy stability (conditional) analysis. It is found that the nonlinear critical stability magnetic thermal Rayleigh number does not coincide with that of the linear instability analysis, and thus indicates that the subcritical instabilities are possible. However, it is noted that, in the case of non-ferrofluid, the global nonlinear stability Rayleigh number is exactly the same as that for linear instability. For lower values of magnetic parameters, this coincidence is immediately lost. The effect of the magnetic parameter M3, coupling parameter N1, and spin diffusion parameter N3, on the subcritical instability region has also been analyzed. It is shown that with the increase of the magnetic parameter (M3) the subcritical instability region between the two theories decreases quickly while with the increase of N1 and N3, the subcritical instability region between the two theories increases. We also demonstrate coupling between the buoyancy and magnetic forces in the nonlinear energy stability analysis as well as in the linear instability analysis.

13

Effect of presence of dust particles on soret-driven ferrothermohaline convection

63%

Sekar R. , Vaidyanathan G. , Hemalatha R.

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2009

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tom Vol. 14, no 2

509-522

EN

Soret driven thermoconvective instability in multicomponent fluids has wide applications in heat and mass transfer. This paper deals with the theoretical investigation of the effect of dust particles on Soret-driven thermohaline convection in a ferrofluid, heated and soluted from below subjected to a transverse uniform magnetic field. An exact solution is obtained for the case of two free boundaries. A linear stability analysis is used. A normal mode technique is applied. Both stationary and oscillatory instabilities are investigated. It is found that the system stabilizes through stationary mode. The non-buoyancy magnetization parameter and the dust particle parameter are found to destabilize the system. The Soret coefficient and the stable solute gradient tend to stabilize the system. The results are presented graphically.

14

From magnetite ore to modern magnetic materials.

51%

Wysłocki J. J.

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2006

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tom Vol. 27, nr 2-3

67-84

EN

The article describes the major stages of research on magnetic materials carried out over the centuries, which have contributed to the discovery and further understanding of new materials. In relation to the above results of investigations carried out in recent years at the Institute of Physics of the Częstochowa University of Technology, concerning the determination of the sources of the magnetic properties and the mechanisms of magnetization of magnetically hard materials, in conjunction with the observations of the domain structure, are presented. Moreover, further interesting results have been obtained from the investigation of the microstructure and magnetic properties of magnetically soft materials - amorphous and nanocrystalline films. New technologies for the production of magnetic materials using the arc-plasma spraying technique and the suction-casting method enabling the production of massive amorphous alloys (bulk amorphous magnetic materials) are also described.

15

Effect of suspensed particles, magnetic field and rotation on thermal stability of ferromagnetic fluids

51%

Aggarwal A. K. , Verma A.

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tom Vol. 17, no. 4

1109-1122

EN

The effect of suspended particles, magnetic field, magnetization and rotation on the thermal stability of a ferromagnetic fluid heated from below is considered. Using a linearized stability theory and normal mode analysis for a fluid layer between two free boundaries, an exact solution is obtained. A dispersion relation governing the effects of suspended particles, magnetic field, magnetization and rotation is derived. For the case of stationary convection, it is found that a suspended particle has a destabilizing effect whereas rotation and magnetization have a stabilizing effect on the system. The magnetic field has a stabilizing effect on the system under certain conditions. The effects of various parameters on the thermal stability are depicted graphically also and the results are in agreement with analytical solutions. The principle of exchange of stabilities is found to hold true for the ferromagnetic fluid heated from below in the absence of rotation and the magnetic field. The oscillatory modes are introduced due to the presence of rotation and the magnetic field which were non-existent in their absence.