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Microscopic modelling of strongly disordered metals: emergent mechanical and magnetic properties

English title Microscopic modelling of strongly disordered metals: emergent mechanical and magnetic properties
Applicant Derlet Peter
Number 196970
Funding scheme Project funding
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Material Sciences
Start/End 01.10.2021 - 30.09.2025
Approved amount 234'964.00
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All Disciplines (3)

Discipline
Material Sciences
Condensed Matter Physics
Mechanical Engineering

Keywords (6)

Defects; Microstructure; Magnetic Properties; Atomistic Modelling; Nanomagnetism; Metals

Lay Summary (German)

Lead
Ein verbessertes Verständnis des Magnetismus in Nanopartikeln zu erreichen, ist eine dringende Aufgabe in der Physik der kondensierten Materie und in den Materialwissenschaften mit Auswirkungen auf eine Vielzahl von Anwendungen, die von der Medizin bis zur Spintronik reichen. Neuere Untersuchungen zeigen, dass übliche Partikeleigenschaften wie Größe und Form nicht stark mit den gemessenen magnetischen Eigenschaften korrelieren. Dies legt nahe, dass andere strukturelle Motive verantwortlich sind, für die es derzeit keine quantitative Beschreibung gibt.
Lay summary

Das zentrale Thema des vorliegenden Promotionsvorhabens ist es, die magnetischen Eigenschaften von Nanopartikeln mit beliebiger, innerer atomarer Struktur, die planare und/oder Liniendefekte beinhalten kann, mit theoretischen Methoden quantitativ zu beschreiben. Um dies zu erreichen, wird eine dreifache Strategie verfolgt: (1) Es wird zunächst untersucht, wie innere Verspannungen die globale magnetische Anisotropie eines Nanopartikels beeinflussen können. (2) Darauf basierend wird eine vollständige atomistische Beschreibung eines magnetischen Teilchens entwickelt, die die relevanten niederenergetischen magnetischen Konfigurationen quantitativ erfasst. (3) Schliesslich werden magnetische Algorithmen zur Exploration der Energielandschaft der Nanoteilchen verwendet, um Energiebarrieren zwischen verschiedenen möglichen magnetischen Konfigurationen zu bestimmen. Das Erreichen dieser Ziele wird es uns erlauben, quantitative Vorhersagen über das magnetische Verhalten von Nanoteilchen mit unterschiedlicher Struktur bei endlichen Temperaturen zu machen und damit die Anwendung von magnetischen Nanoteilchen zu optimieren. Die Arbeiten werden eng an die laufenden Experimente an den Grossanlagen des Paul Scherrer Instituts anknüpfen.

 

Direct link to Lay Summary Last update: 28.06.2021

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Abstract

The mechanical and magnetic functional properties of engineering-relevant crystalline metals depend on the collective features of the underlying microstructure. Microstructure, realized as a distribution of point, line and planar defects, can introduce new energy scales with respect to emergent structural and magnetic length scales. This microstructure can be characterized by the potential energy landscape (PEL) which will have contributions from both the core regions of the defects and the long-range elastic strain fields that they entail. Whilst both are important, for complex microstructures with a high density of defects, the latter internal stress/strain component can dominate a material's collective and macroscopic response to a local or global perturbation. Investigation of this aspect, and its relationship to the functional properties of mono-atomic metals is the central scientific theme of the present SNSF proposal. To do this, the proposal focuses on the microscopic modelling of two very different material geometries and functional properties, one in which the important length-scale is set by an internal micro-structural feature, and the other by sample size, with both containing a non-trivial microstucture. The first case will focus on heavily irradiated transition metals (Fe and W), where experimentally it is known that high dose ion/neutron/electron irradiation can produce a multi-scale microstructure whose full characterization and dynamics remains both an experimental and modelling challenge. In such complex microstructures, the internal elastic strain and its associated length scale can become the dominant energy scale which ultimately controls its emergent mechanical properties. The second case will focus on the thermally active magnetic properties of small metallic clusters (Fe, Ni, Co). Ongoing experimental work at the Paul Scherrer Institute (PSI) using advanced synchrotron and electron microscopy methods concludes that not only the size and shape of the magnetic particles, but also their internal defect structure can effect magnetic behaviour. This suggests internal strain via the structural PEL affects the magnetic PEL (through magneto-elastic coupling), and in turn the thermally driven magnetic switching properties.The proposal therefore requests funding for two PhDs: 1) To perform large-scale molecular dynamics simulations to investigate the internal stress/strain landscape of heavily irradiated model single crystal and poly-crystalline environments, and to characterize its observed emergent stress-driven mechanical properties; and 2) To implement a microscopic magneto-elastic simulation methodology to determine the thermal switching properties of a magnetic particle containing an internal strain field due to its finite geometry and/or its defect content. These projects will use state-of-the-art microscopic structural and magnetic simulation methods to characterize the corresponding PELs in terms of emergent energy and length scales. For the calculation of thermal magnetic switching timescales, harmonic transition rate theory will be used. The expected results will relate internal strain scales to emergent stress-driven mechanical and thermally-driven magnetic functionalities. The impact of project 1 will be an improved and more accurate knowledge of how materials behave in extreme irradiation environments, and in project 2 it will aid in the development of novel spintronics devices and new magnetic storage approaches which are stable at room temperature.
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