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1
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Interval Computations of Ferromagnetic Resonance Conditions in Exchange-Biased Bilayers

100%
Gutowski M., Żuberek R.
Acta Physica Polonica A
|
2009
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vol. 115
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issue 1
390-392
EN
The main purpose of this paper is to promote the use of interval calculus in physics. As an example we use the system consisting of two thin films, one ferromagnetic and another one antiferromagnetic, deposited one atop of the other. We successfully and accurately simulate the positions of resonance fields of such a system, as seen in ferromagnetic resonance experiment. Interval calculations have revealed the presence of 1, 2 and sometimes even 4 distinct equilibrium configurations of the system, all corresponding to the same resonance field, when the field has a component antiparallel to that of cooling field, while only 1 such position when it points in the opposite direction. In both cases only a single resonance line is observed. As an added value we show that the exchange-biased system is in the metastable state, out of true thermodynamical equilibrium.
2
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Role of Crystal-Melt Interface and Surface Tension on Czochralski Growth of Substrate Materials with K_{2}NiF_{4} Structure

81%
Berkowski M., Fink-Finowicki J., Gutowski M.
Acta Physica Polonica A
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1997
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vol. 92
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issue 1
197-200
EN
Crystal-melt interface was investigated during Czochralski growth of SrLaGaO_{4} and SrLaAlO_{4} crystals on ⟨001⟩ oriented seeds. Relations between the ratio of the core diameter, grown on (001) plane, and the crystal diameter, as a function of seed rotation speed were determined. It was confirmed that it is possible to control the core diameter during the crystal growth. A new module was introduced into the crystal growth controlling program. It enables to estimate the surface tension coefficient between crystal and melt at the beginning of crystallization. This value is then used to compute proper corrections for automatic weighting system.
3
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Magnetic Flux Density and Radial Distribution of Currents in HTSC Samples of Specific Shape Determined by Genetic Algorithm

81%
Piotrowski K., Gutowska M. U., Gutowski M.
Acta Physica Polonica A
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1997
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vol. 92
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issue 1
259-262
EN
Flux distribution in a Bi_{2}Sr_{2}CaCu_{2}O_{8} superconductor sample, shaped as a thin disk with a hole in the center, and covered with a thin layer of magnetic garnet, was observed by means of magneto-optical Faraday effect. Applying external magnetic field perpendicularly to the sample plane with zero field cooling history, we were able to observe the flux trapped in superconductor, visible as concentric rings. Both directions of the trapped field were observed near the sample surface. Using the genetic algorithm we were able to determine the radial distribution of concentric currents in the sample under study.
4
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Preisach Images of a Simple Mechanical System

81%
Gutowski M., Markovskyi S., Chyao A.
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EN
This work is an an early stage of a larger project aiming at answering the question whether or not the Preisach map is really fingerprinting magnetic materials. More precisely, we are interested whether the Preisach model of magnetic hysteresis indeed contains any physics or is just a convenient modeling tool. To this extent we study a very simple mechanical system, thus fully tractable, subjected to the external force. Despite of its simplicity, our model captures all the fundamental features of real magnetic materials, namely their hysteretic behavior, coercivity, remanent magnetization, and saturation at high fields. Both the overall shape of major hysteresis loop as well as first order reversal curves are reproduced quite correctly; they are very similar to those observed in magnetic materials. The model essentially consists of a single, spring loaded, rigid and rotative bar with non-zero friction torque. The length of a projection of this bar onto the direction of an external force is identified with magnetization. The friction torque and the spring constant are the only freely adjustable parameters of our model. Here we investigate, and present, their influence on the inferred Preisach maps.
5
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Preisach Maps of Multilayered Co/Cu Structures

71%
Gutowski M., Gutowska M., Piotrowski K., Baczewski L., Wawro A.
Acta Physica Polonica A
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2000
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vol. 97
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issue 3
467-470
EN
Magnetooptical Kerr effect measurements of room temperature hysteresis loops were taken using sandwich- and multilayer-type specimens and He-Ne laser light. For maximal external field of ~250 Gs the corresponding Kerr angle reached 0.04 deg. The samples were obtained in the Institute of Physics, Polish Academy of Sciences, Warszawa, using MBE method. The structure of samples may be described by a formula: substrate-buffer layer-(xCo/yCu)_{n} -cover layer. Al_{2}O_{3} (two orientations) and MgO were used as substrates, the buffer layer was made of W, Cu or Fe, x=15, 20 or 25 Å, y=7, 8, 9, 10, 11, 12, 13, 14, and 20 Å, n=25 and 30. 50 Å of gold (Au) served as a cover layer. The genetic algorithm was subsequently used as a data processing tool, in order to reconstruct the Preisach map for each hysteresis loop. The diagrams clearly indicate changes of magnetic interactions caused by varying thicknesses of individual magnetic and non-magnetic layers.
6
Content available remote

Interval Identification of FMR Parameters for Spin Reorientation Transition in (Ga,Mn)As

61%
Gutowski M., Stefanowicz W., Proselkov O., Sawicki M., Żuberek R., Sadowski J.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1228-1230
EN
In this work we report results of ferromagnetic resonance studies of a 6% 15nm (Ga,Mn)As layer, deposited on (001)-oriented GaAs. The measurements were performed with in-plane oriented magnetic field, in the temperature range between 5 K and 120 K. We observe a temperature induced reorientation of the effective in-plane easy axis from [\overline{1}10] to [110] direction close to the Curie temperature. The behavior of magnetization is described by anisotropy fields, H_{eff} (=4π M-H_{2⊥}), H_{2∥}, and H_{4∥}. In order to precisely investigate this reorientation, numerical values of anisotropy fields have been determined using powerful - but still largely unknown - interval calculations. In simulation mode this approach makes possible to find all the resonance fields for arbitrarily oriented sample, which is generally intractable analytically. In "fitting" mode we effectively utilize full experimental information, not only those measurements performed in special, distinguished directions, to reliably estimate the values of important physical parameters as well as their uncertainties and correlations.
7
Content available remote

Temperature Dependence of Exchange Anisotropy of FeNi/FeMn Bilayers

61%
Żuberek R., Gutowski M., Szymczak H., Gnatchenko S., Merenkov D., Bludov A., Verkin B.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
167-170
EN
The influence of the bilinear and biquadratic coupling on the exchange anisotropy of the ferromagnetic/antiferromagnetic bilayer was studied by variable angle and temperature dependent ferromagnetic resonance. From the angular dependence of the resonance field the bilinear and biquadratic exchange coupling constants were determined.
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