Wyniki wyszukiwania - BazTech

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Magnetic properties of cementite (Fe3C) nanoparticle agglomerates in a carbon matrix

Lipert K., Kaźmierczak J., Pełech I., Narkiewicz U., Ślawska-Waniewska A., Lachowicz H. K.

Materials Science Poland

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2007

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Vol. 25, No. 2

399--404

EN

Magnetic properties of two FeC samples with different amounts of carbon have been studied. In both cases, the amount of carbon was well above the mass sufficient to transform nanocrystalline iron into iron carbide (cementite). Through the dc magnetic and transmission electron microscopy (TEM) measurements it was shown that cementite nanoparticles formed agglomerates; the size distribution of these nanoparticles was very wide, and superparamagnetic-like behaviour was not observed even at room temperature.

2

Wspomnienia sprzed lat czterdziestu

Lachowicz H. K.

Prace Instytutu Technologii Elektronowej

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2006

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z. 1

7-9

3

Influence of alternating circular magnetic field strength on magnetoimpedance of glass-coated micro-wire

Kuźmiński M., Lachowicz H. K., Garcia K. L., Zhukov A., Vazquez M.

Journal of Technical Physics

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2005

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Vol. 46, no 3

165-173

EN

The presented experiments on giant magnetoimpedance (GMI) effect were carried out using glass-coated amorphous micro-wire specimen of its diameter of 22.4 urn and nominal composition of Co67Fe3.85Ni1.45Mo1.7Si14.5B11.5. The main purpose of these experiments was to demonstrate the influence of the AC-current intensity flowing along this specimen and generating circular alternating magnetic field, on the properties of the GMI-effect. To demonstrate this, the GMI-ratio was measured vs. axial DC-field at various intensities of the AC-current ranging from 0.3 up to 5 mA, the range which corresponds to the intensity of the circular field of around 4.8 - 80 A/m at the surface of the micro-wire. The obtained dependences showed that the maximum of the GMI-ratio occurs at the intermediate intensity of the circular field, around 24 A/m (identified with the threshold field of the micro-wire specimen magnetized in the circumferential direction). This result was confirmed analyzing the dependences of the wire impedance plotted vs. the intensity of AC-current for different selected DC-field as a parameter. The results were interpreted considering the expected domain structure in the wire, in particular, that its surface layer was composed of the stripe domains magnetized circumferentially, alternately in opposite directions ("bamboo structure"). Such a structure is created by the magnetoelastic anisotropy. In order to make this explanation more reliable, the penetration depth of the skin-effect was calculated on the grounds of the classical model. Analysis of the AC-field dependence of the penetration depth additionally confirmed the presented interpretation. The main conclusion which can be drawn from the performed experiments is that, in order to achieve optimum parameters of the GMI from the view-point of application in sensors, AC-current intensity should appropriately be chosen.

4

The effect of axial dc-field on transverse permeability in Co-based metallic glass ribbons

Lachowicz H. K., Kuźmiński M., Yu S. C.

Materials Science

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2003

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Vol. 21, No. 1

123-132

EN

A simple geometrical model is proposed. This model allows to calculate the penetration depth and the mean transverse permeability in magnetic elements of a rectangular cross-section which are used to study the giant magnetoimpedance effect (GMI). As an instance of the use of this model, both the mentioned quantities were calculated for the Co-based metallic glass ribbon using the experimental data obtained for the Co-based metallic glass ribbons. Their evolution with the applied axial dc-field at various frequencies of the ac-current, flowing along the ribbon, is presented. A comparison of the experimental data with those calculated by the model, shows that the latter gives only a qualitative approximation of the measured dependencies.

5

Large magnetocaloric effect in perovskite manganites: magnetic entropy changes above 300 K

Phan M. H., Yu S. C., Ulyanov A. N., Lachowicz H. K.

Materials Science

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2003

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Vol. 21, No. 1

133-139

EN

We present here, the results of an investigation of the large magnetic entropy change, M S D , above 300 K in a series of La0.65Sr0.35MnO3, La0.6Sr0.2Ca0.2MnO3, La0.6Sr0.2Ba0.2MnO3, La0.7Ba0.3MnO3 and La0.7Ba0.24Ca0.06MnO3 perovskite manganites. Among the studied compositions, La0.6Sr0.2Ba0.2MnO3 exhibits a highest value of 2.26 J/kg/K for |ASMmax| at the Curie temperature, TC = 354 K, when the field is changed from 0 to 10 kOe. The adiabatic temperature change, ATad, of this sample is ~ 1.1 K and ~ 4.95 K in the fields of 10 kOe and 50 kOe, respectively. Since the large magnetocaloric effect was found in the present materials with above 300 K Curie temperature, these materials seem to be attractive for above room temperature magnetic refrigeration applications.

6

Materiały magnetyczne - postęp i wyzwania

Lachowicz H.K.

Przegląd Elektrotechniczny

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2002

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R. 78, nr 11

287-291

PL

W artykule przedstawiono przegląd nowoczesnych materiałów, miękkich i twardych pod względem magnetycznym. W przypadku magnetyków miękkich skoncentrowano się na szkłach metalicznych (materiały amorficzne) oraz materiałach nanokrystalicznych, które, choć znane już od dłuższego czasu, to jednak nadal charakteryzują się najlepszymi parametrami w swej klasie. W przypadku magnetyków twardych, główną uwagę poświęcono związkom międzymetalicznym typu Nd-Fe-B, wykorzystywanym do budowy magnesów trwałych o najlepszych dziś parametrach użytkowych (największa gęstość objętościowa energii magazynowanej w magnesie). Przedstawiono właściwości magnetyczne obydwu omawianych klas materiałów, ich typowe zastosowania oraz kierunki badań, których celem jest opracowanie nowych materiałów bądź też ulepszenie istniejących.

EN

The present paper gives a review of novel materials, magnetically soft and hard. In the case ot soft magnets, the review is focused on metallic glasses (amorphous materials) and nanocrystalline materials, the latter fabricated by crystallization of the parent metallic glass. Though, they were developed years ago, nevertheless these materials display so tar the best soft magnetic properties among the existing materials of this class. In the case of hard magnets, attention is mainly given to inter-metallic compounds of Nd-Fe-B type used to manufacture permanent magnets of actually best utilizable parameters (highest energy product). Magnetic properties of the considered materials and their typical applications are presented. The research efforts towards invention of novel materials or improvement of the existing ones are also shown.

7

Partially devitrified metallic glasses

Lachowicz H. K., Zaveta K., Ślawska-Waniewska A.

Journal of Technical Physics

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2002

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Vol. 43, no 4

527-542

EN

The paper presents a review of selected experiments which have been carried out using partially devitrified Fe- and Co-based metallic glasses as the research objects. It is shown that by a suitable choice of the composition of the metallic glass and also by the conditions of annealing, a variety of magnetic phases can be created in these systems. It is also shown that by controlled processes of annealing, the coercivity of metallic glass can be altered by several orders of magnitude, giving a possibility to produce materials with the extremely soft magnetic properties, up to the magnetically semi-hard ones. The magnetostriction of nanocrystalline materials of the FINEMET-type is discussed as well, showing that the size-dependent phenomena and the symmetry restriction at the particle boundaries create the surface contribution to the effective magnetostriction. Finally, the magnetic interactions between particles in partially devitrified samples are considered and the observed effects of temperature and hydrostatic pressure discussed.

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Gigantyczna magnetoimpedancja i jej zastosowania

Lachowicz H. K.

Elektronika : konstrukcje, technologie, zastosowania

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2002

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Vol. 43, nr 9

3-6

PL

Przedstawiono zjawisko gigantycznej magnetoimpedancji (GMI) podając wyrażenia opisujące to zjawisko dla różnych zakresów częstotliwości prądu płynącego przez magnetyczny element czynny. Pokazano przykładowe charakterystyki GMI, uzyskane dla taśmy szkła metalicznego zawierającej kobalt jako główny składnik. Podano przykłady praktycznego wykorzystania zjawiska GMI w sensorach wielkości elektrycznych i nieelektrycznych.

EN

Giant magnetoimpedance (GMI) effect is presented. Theoretical expressions describing this effect in different ranges of frequency of electric current flowing through the active magnetic element are given. Exemplary GMI-characteristics obtained for Co-rich metallic glass ribbon are shown. Practical utilization of GMI-effect in sensors of electrical and non-electrical quantities are shown being exemplified by a number of possible applications.

9

GMR-effect in granular Co-Cu structure at elevated temperatures

Kuźmiński M., Ślawska-Waniewska A., Lachowicz H. K., Kulik T.

Electron Technology

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1999

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Vol. 32, No. 4

338-342

EN

Transport and magnetic properties of the annealed melt-spun Cu₉₀Co₁₀ granular alloy were investigated at elevated temperatures. Complex intrinsie structure of the sample manifests itself in the observed giant magnetoresistance (GMR) characteristics. It is shown that the measured field and teperature dependencies of GMR are strongly influenced by the distribution of the size of superparamagnetic particles and by the presence of the residsual ferromagnetic phase ( much larger particles or agglomerations of smaller particles).