Lecture

Magnetic Anisotropy in Crystalline Materials

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In course

PHYS-407: Frontiers in nanosciences

The course covers relevant experimental and theoretical concepts in nanoscale science, from fundamental aspects like quantum tunneling and quantum size effects, to hot topics like quantum transport and nanoscale magnetism. ...

Description

This lecture delves into the concept of magnetic anisotropy in crystalline materials, exploring how the orientation of magnetization is influenced by the crystal structure. The instructor explains the origin of magnetic moments in atoms, the interactions between spins, and the factors determining the preferred direction of magnetization in grains. The discussion covers the effects of shape anisotropy and the magnetic anisotropy energy, crucial for understanding the stability of magnetic systems. The lecture also touches on quantum tunneling of magnetization and the experimental techniques used to measure the spin and orbital moments separately.

Instructors (4)

Klaus Kern

Klaus Kern is Professor of Physics at EPFL and Director and Scientific Member at the Max-Planck-Institute for Solid State Research in Stuttgart, Germany. He also is Honorary Professor at the University of Konstanz, Germany. His present research interests are in nanoscale science, quantum technology and in microscopy at the atomic limits of space and time. He holds a chemistry degree and PhD from the University of Bonn and a honorary doctors degree from the University of Aalborg. After his doctoral studies he was staff scientist at the Research Center Jülich and visiting scientist at Bell Laboratories, Murray Hill before joining the Faculty of EPFL in 1991 and the Max-Planck-Society in 1998. Professor Kern has authored and coauthored close to 700 scientific publications, which have received nearly 60‘000 citations. He has served frequently on advisory committees to universities, professional societies and institutions and has received numerous scientific awards and honors, including the 2008 Gottfried-Wilhelm-Leibniz Prize and the 2016 Van‘t Hoff Prize. Prof. Kern has also educated a large number of leading scientists in nanoscale physics and chemistry. During the past twenty-five years he has supervised one hundred PhD students and sixty postdoctoral fellows. Today, more than fifty of his former students and postdocs hold prominent faculty positions at Universities around the world.

Stefano Rusponi

Education: • 1999 Doctoral degree in Physics obtained at the Physics Department, University of Genova PhD thesis title: “STM study of nanostructures induced by ion sputtering on noble metals”. • 1994 University degree in Physics achieved at the Physics Department, University of Genova. Final mark: 110/110 cum laude Diploma thesis title: “A project for a new method of EELS spectroscopy”. • 1988 High school at the Liceo Scientifico G. P. Vieusseux in Imperia. Final mark: 60/60. Research career plan: • 2016 – present MER: Ecole Polytechnique Fédérale de Lausanne (EPFL) in the group of Prof. Harald Brune • 2003 – 2016: 1er. Assistant: Ecole Polytechnique Fédérale de Lausanne (EPFL) in the group of Prof. Harald Brune • 2000-2003: Assistant: Ecole Polytechnique Fédérale de Lausanne (EPFL) under the direction of Prof. Harald Brune • 1999-2000: Research associate: Max-Planck-Institut of Stuttgart under the direction of Prof. Klaus Kern Miscellaneous of professional activities: a) Review panel • Member of the Elettra proposal review panel • Member of the committee of the EDPY doctoral school in Physics at the EPFL b) Co-worker in the building of the X-Treme beamline: c) Referee for scientific journals: • Nat. Commun., Phys. Rev. Lett., Phys. Rev. B, J. Appl. Phys., Surf. Sci., J. Magn. Magn. Mater. Funding record a) Funding awarded • Quantum Properties of Nanostructures at Surfaces, FNS 200020-157081/1; (01/10/2014 – 31/09/2017); total amount attributed: 832'558 CHF; co-applicant • Controlling magnetic anisotropy by interfacial coupling, FNS 200021_146715/1; (01/01/2014 – 31/12/2016); total amount attributed: 367'800 CHF; co-applicant • Self-assembled bi-metallic magnetic pillar superlattices with enhanced blocking temperature, SER C10.0135; (01/08/2011 – 01/08/2013); total amount attributed: 170'000 CHF; co-applicant • Magnetic and Catalytic Properties of Surface Supported Metallic Nanostructures, FNS 200020-120493/1; (01/04/2008 – 31/03/2010); total amount attributed: 402'669 CHF; co-applicant • Magnetic and Catalytic Properties of Surface Supported Metallic Nanostructures, FNS 200020-112322/1; (01/04/2006 – 31/03/2008); total amount attributed: 347'633 CHF; co-applicant b) Approved proposals for the allocation of beamtime Swiss Light Source (SLS): main proposer: 9 co-proposer: 4 Elettra: main proposer: 5 co-proposer: 1 European Synchrotron Radiation Facility (ESRF): main proposer: 2 co-proposer: 11 Student supervisor • Co-director of PhD thesis: 4 PhD students

Dimitris Mousadakos: Seeking the smallest room temperature magnets; (in progress)
Romana Baltic: Controlling single atom magnetic anisotropy by interfacial coupling; (in progress)
Alberto Cavallin: Growth and magnetism of nanostructures investigated by STM, MOKE, and XMCD; (Oct. 2013), Thèse N°5941
Sergio Vlaic: Magnetism and atomic scale structure of bimetallic nanostructures at surfaces; (Dec. 2012), Thèse N° 5625

• Supervisor of PhD thesis (without co-direction): 4 PhD students

Anne Lehnert: Magnetism of individual adatoms and of epitaxial monolayers; (Jun. 2009), Thèse N° 4411
Geraud Moulas: Growth and magnetism of 2D bimetallic nanostructures; (Dec. 2008), Thèse N° 4231
Philipp Buluschek: Submonolayer growth of cobalt on metallic and insulating surfaces studied by scanning tunneling microscopy and kinetic Monte-Carlo simulations; (Nov. 2007), Thèse N° 3944
Nicolas Weiss: Propriétés magnétiques de nanostructures de Co adsorbées; (Apr. 2004), Thèse N° 2980

• Supervisor of Master thesis: 6 students • Supervisor of semester projects: 9 students • PhD thesis referee: 2 students

Official source

Ontological neighbourhood

Physics

Condensed matter physics: Phase transitions

Related concepts (18)

Magnetic susceptibility

In electromagnetism, the magnetic susceptibility (; denoted χ, chi) is a measure of how much a material will become magnetized in an applied magnetic field. It is the ratio of magnetization M (magnetic moment per unit volume) to the applied magnetizing field intensity H. This allows a simple classification, into two categories, of most materials' responses to an applied magnetic field: an alignment with the magnetic field, χ > 0, called paramagnetism, or an alignment against the field, χ < 0, called diamagnetism.

Magnetocrystalline anisotropy

In physics, a ferromagnetic material is said to have magnetocrystalline anisotropy if it takes more energy to magnetize it in certain directions than in others. These directions are usually related to the principal axes of its crystal lattice. It is a special case of magnetic anisotropy. In other words, the excess energy required to magnetize a specimen in a particular direction over that required to magnetize it along the easy direction is called crystalline anisotropy energy.

Magnetic domain

A magnetic domain is a region within a magnetic material in which the magnetization is in a uniform direction. This means that the individual magnetic moments of the atoms are aligned with one another and they point in the same direction. When cooled below a temperature called the Curie temperature, the magnetization of a piece of ferromagnetic material spontaneously divides into many small regions called magnetic domains. The magnetization within each domain points in a uniform direction, but the magnetization of different domains may point in different directions.

Crystallinity

Crystallinity refers to the degree of structural order in a solid. In a crystal, the atoms or molecules are arranged in a regular, periodic manner. The degree of crystallinity has a big influence on hardness, density, transparency and diffusion. In an ideal gas, the relative positions of the atoms or molecules are completely random. Amorphous materials, such as liquids and glasses, represent an intermediate case, having order over short distances (a few atomic or molecular spacings) but not over longer distances.

Ferromagnetism

Ferromagnetism is a property of certain materials (such as iron) that results in a significant, observable magnetic permeability, and in many cases, a significant magnetic coercivity, allowing the material to form a permanent magnet. Ferromagnetic materials are familiar metals that are noticeably attracted to a magnet, a consequence of their substantial magnetic permeability. Magnetic permeability describes the induced magnetization of a material due to the presence of an external magnetic field.

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