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Nanocrystalline Fe-Pt alloys: phase transformations, structure and magnetism

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Nanocrystalline Fe-Pt alloys: phase transformations, structure and magnetism (English shop)

Julia Lyubina (Author)

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ISBN-13 (Printausgabe) 3867272336
ISBN-13 (Hard Copy) 9783867272339
ISBN-13 (eBook) 9783736922334
Language English
Page Number 136
Edition 1
Volume 0
Publication Place Göttingen
Place of Dissertation Dresden
Publication Date 2007-05-16
General Categorization Dissertation
Departments Physics
Keywords L10 FePt, ordered alloys, nanocrystalline materials, permanent magnets, magnetisation processes, neutron diffraction, x-ray diffraction.
Description

This work has been devoted to the study of phase transformations involving chemical ordering and magnetic properties evolution in bulk Fe-Pt alloys composed of nanometer-sized grains. A comprehensive study of phase transformations and ordering in Fe-Pt alloys is performed by a combination of in-situ neutron powder diffraction and thermal analysis. The dependence of ordering processes on the alloy composition and initial microstructure (homogeneous A1 phase or multilayer-type) is established. Through the use of mechanical alloying and subsequent heat treatment it has been possible to achieve the formation of chemically highly ordered L10 FePt and, in the case of the Fe-rich and Pt-rich compositions, L12 Fe3Pt and FePt3 phases, respectively. Whereas in Pt-rich alloys the decoupling effect of the FePt3 phase leads to coercivity improvement, in Fe-rich nanocomposites a peculiar nanometer scale multilayer structure gives rise to remanence enhancement due to large effects of exchange interactions between the crystallites of the phases. The structure, magnetic properties and magnetisation reversal processes of these alloys are investigated. Experimentally observed phenomena are understood on the basis of a simple two-particle interaction model. Neutron diffraction has also been used for the investigation of the magnetic structure of ordered and partially ordered nanocrystalline Fe-Pt alloys. It has been shown that the magnetic moment of Fe atoms in L10-type Fe Pt alloys is sensitive to the compositional order. The results are compared to density functional calculations.