magistrsko delo
Darja Gačnik (Author), Janez Dolinšek (Mentor)

Abstract

V magistrskem delu obravnavamo magnetizem visokoentropijske zlitine FeCoNiPdCu. Najprej so opisane splošne značilnosti visokoentropijskih zlitin, nato pa še nekateri pomembni magnetni pojavi in koncepti ter kratek opis vpliva električne upornosti na delovanje magnetov v magnetnih aplikacijah. Sledi opis eksperimentalnih metod in merilnih aparatur, ki so bile uporabljene pri poskusih. Uporabljene so bile naslednje eksperimentalne metode: rentgenska difrakcija za določitev kristalne strukture zlitine, elektronska mikroskopija za določitev njene mikro- in nanostrukture, meritev tempe-raturno-odvisne magnetizacije za določitev Curiejeve temperature prehoda iz fero-magnetnega v paramagnetno fazo in meritev magnetizacijskih histereznih krivulj za določitev vrednosti koercitivnosti in nasičene magnetizacije v visokem magnetnem polju. Magnetne meritve in meritev električne upornosti so bile za primerjavo izvede-ne tudi z vzorcem iz komercialnega mehkega magneta, t.j. neurejene elektropločevine iz silicijevega jekla, ki se uporablja v statorjih elektromotorjev in v jedrih transforma-torjev. V magistrskem delu so predstavljeni ključni rezultati meritev. Iz analize struk-turnih meritev je razvidno, da je material FeCoNiPdCu zgrajen iz nanostruktur veli-kosti od dveh do petih nanometrov. Le-te so v materialu prisotne v dveh različnih kompozitnih fazah: FeCoNi kristalni nanostrukturi in PdCu kristalni nanostrukturi. Ti dve različni fazi sta po vzorcu razporejeni naključno. Nastanek kompozitnih faz je energijsko ugoden zaradi specifičnih vrednosti binarne mešalne entalpije posameznih parov elementov. FeCoNi struktura vsebuje atome železa, kobalta in niklja, katerih magnetne lastnosti povzročijo, da so tudi FeCoNi strukture magnetne. Zaradi majh-nosti nanostruktur so magnetni momenti gradnikov FeCoNi struktur poravnani v eno smer, zato FeCoNi strukture predstavljajo magnetne domene. PdCu kristalne nanostrukture gradijo nemagnetni atomi paladija in bakra. Med gradniki nanostruk-tur je prisotna izmenjalna sklopitev, ki zaradi njihove majhnosti povzroči efekt pov-prečenja izmenjalne anizotropije. To se na makroskopski skali kaže v skoraj ničelni vrednosti koercitivnosti, kar smo potrdili tudi z rezultati magnetnih meritev. Iz anali-ze meritev je mogoče zaključiti, da so vzrok magnetne mehkosti materiala FeCo-NiPdCu magnetni pojavi na nanoskali, bolj specifično povprečenja izmenjalne mag-netne anizotropije. Izkazalo se je tudi, da so magnetne lastnosti materiala FeCo-NiPdCu primerljive z magnetnimi lastnosti neorientirane elektropločevine in ostalih komercialno uporabljenih mehkih magnetov. Rezultati magistrskega dela podajajo novo razumevanje magnetizma visokoentropijske spojine FeCoNiPdCu, s katerim bo mogoče v prihodnje bolje razumeti magnetizem drugih visokoentropijskih spojin.

Keywords

fizika trdne snovi;visokoentropijske spojine;mehki feromagneti;nanokompoziti;magnetne lastnosti;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL FMF - Faculty of Mathematics and Physics
Publisher: [D. Gačnik]
UDC: 538.9
COBISS: 3237220 Link will open in a new window
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Downloads: 337
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Other data

Secondary language: English
Secondary title: Soft ferromagnetism of high-entropy alloy FeCoNiPdCu
Secondary abstract: In this master thesis we present the study of magnetism of high-entropy alloy FeCo-NiPdCu. First we introduce general properties of high-entropy alloys. Afterwards we explain some important magnetic concepts and then briefly describe the influence of electrical resistivity on magnet performance in magnetic applications. Later on we list measurement devices and experimental methods used for experiments. Among them the main are X-ray diffraction, used for crystal lattice determination, electron mi-croscopy for micro- and nanostructure specification, temperature dependent magnet-ization measurement for Curie temperature evaluation and magnetization hysteresis loops measurements for depicting coercivity and saturation magnetization values in high magnetic field. Magnetic measurements and the measurement of electrical resis-tivity were performed also with a non-oriented electrical steel, which is a commercial soft magnet used in electromotor stators and in the cores of transformers. This mas-ter thesis includes the main experimental results. From the analysis of structural measurements it is evident that the FeCoNiPdCu material is a composite of nanostructures that are from two to five nanometers in size. Nanostructures have two different compositional phases, FeCoNi and PdCu phase that are intermixed completely randomly. These nanostructures form due to energetically favorable mix-ing of specific pairs of elements which is explained by their binary mixing enthalpies. On one hand, FeCoNi phase consists of magnetic elements iron, cobalt and nickel which contributes to magnetic behavior of these nanostructures. Not only that, these structures are so small that all consisting atomic magnetic moments are aligned and nanostructures form magnetic domains. On the other hand, PdCu phase consist of non-magnetic palladium and copper atoms. Due to the nano-size of nanostructures an exchange coupling between the atoms causes the effect of averaging exchange anisotropy. This causes coercivity of the material to be near-zero, which we also con-firmed with the magnetic measurements. From the measurement analysis we can conclude that the cause for soft magnetic properties of FeCoNiPdCu lies in the na-noscale magnetism effects. We also compared its magnetic properties to other soft magnetic materials, e.g. non-oriented electrical steel, and concluded that its soft magnetic properties are in the same range as for other materials. Results of experi-mental work offer a new understanding of high-entropy alloy FeCoNiPdCu and could contribute to deeper understanding of magnetism of high-entropy alloys in general.
Secondary keywords: solid state physics;high-entropy alloys;soft ferromagnets;nanocomposites;magnetic properties;
Type (COBISS): Master's thesis/paper
Study programme: 0
Thesis comment: Univ. v Ljubljani, Fak. za matematiko in fiziko, Oddelek za fiziko
Pages: 71 str.
ID: 10959598