Magnetism and Quantum Materials

We apply several experimental techniques:

Neutron scattering is central to our activities within fundamental research, and is complemented by investigations of bulk magnetic properties and synchrotron x-ray studies. 

We are leading the construction of the BIFROST spectrometer at the European Spallation Source (ESS) in Lund. The BIFROST construction project runs from 2016 to 2022, and the instrument will be ready when ESS user operation commences in 2023. 

In-house experimental facilities includes Mössbauer spectroscopy. 

We benefit from the electron microscopy facilities incl. electron holography next door at DTU CEN. Furthermore, we have access to a 9 Tesla Physical Properties Measurement System at DTU Chemistry, and a 16T Properties Measurement System at DTU Energy.

Current activities

Our on-going research interests are:

• Magneto-electric and multiferroic materials, in which electrical and magnetic properties are coupled, giving rise to perspectives for new applications, e.g. within information technology. I particular, we focus on understanding the response of these materials when large magnetic fields are applied.

• Experimental studies of magnetic nanoparticles, incl. studies of novel aspects of crystal growth, for new applications of magnetic nanoparticles, incl. design of new materials.

 They also include

• The study of electronic self-organization in high-temperature copper-oxide superconductors, i.e. spin and charge density wave order and their interplay with superconductivity

• Quantum magnetism, i.e. the study of specific quantum mechanical effects that go beyond the semi-classical theories of magnetism

• Neutron scattering instrumentation related to the BIFROST spectrometer at ESS

• Magnetic properties of individual and interacting nanoparticles for biomedical and catalytic applications

Fig. 1. Electron holography imaging of dipolar magnetism in self-assembled 15 nm Co nanoparticle chains recorded at remanence before and after magnetic saturation. Nanoparticle magnets behave differently from conventional magnets and their properties may be controlled and tuned by selecting the arrangement and compositions of the constituent nanoparticles. From M.Varon, M. Beleggia, T. Kasama, R.J. Harrison, R.E. Dunin-Borkowski, V.F. Puntes, and C. Frandsen, Dipolar magnetism in ordered and disordered low-dimensional nanoparticle assemblies, Scientific Reports 3 (2013) 1234. 

Fig. 2. Computer simulations of super-structure domain walls in two-dimensional assemblies of magnetic nanoparticles. The domain wall evolution is simulated during magnetic field reversal. Initially (a) the magnetization of the particles points to the right (blue colors). We see how longitudinal domain walls are  stabilized during magnetization reversal (b, c).  From J. Jordanovic, M. Beleggia, J. Schiøtz, and C. Frandsen, Journal of Applied Physics 118 (2015) 043901.

The BIFROST spectrometer at ESS

DTU Physics is leading the construction of the BIFROST spectrometer at the European Spallation Source (ESS) in Lund Sweden.

The construction project runs from 2016 to 2022. BIFROST is expected to be ready when the ESS user program starts in 2023. The construction project is a collaboration between DTU Physics, the Niels Bohr Institute at the University of Copenhagen, the Paul Scherrer Institute (PSI) in Switzerland, Laboratoire Léon Brillouin (LLB) in France and the Institute of Energy Technology (IFE) in Norway.

BIFROST is an innovative indirect time-of-flight spectrometer and is expected to out-perform present world-leading instruments by more than a factor of 30. The science case of BFIROST centers primarily on problems related to magnetism and quantum materials, but the very large flux of BIFROST will also enable novel geoscience and bioscience.

Collaborations

All our work is conducted in terms of international collaboration. Our present main scientific connections include

• The Paul Scherrer Institute (PSI), Switzerland
• Helmholtz-Zentrum Berlin für Materialien Und Energie (HZB), Germany
• University of Zürich, Switzerland
• EPFL Lausanne, Switzerland
• Ames Laboratory, USA
• UC Berkeley, USA
• UC London, UK
• NTNU Trondheim, Norge

In Denmark we collaborate with:

• DTU Chemistry
• DTU Energy
• DTU CEN
• DTU Nanotech
• DTU MEK
• Niels Bohr Institute, University of Copenhagen
• Department of Chemistry, University of Copenhagen
• Department of Physics and Chemistry, University of Southern Denmark
• iNano, University of Aarhus

Fig. 3. Quantized spin waves in magnetic nanoparticles observed by neutron scattering, from E. Brok, C. Frandsen, D.E. Madsen, H. Jacobsen, J. O. Birk, K. Lefmann, J. Bendix, K. S. Pedersen, C. Boothroyd, A.A. Berhe, G.G. Simeoni, and S. Mørup, Magnetic properties of ultra-small goethite particles, J. Phys. D: Appl. Phys. 47 (2014) 365003.  See the article here.

Experimental work at large scale facilities

Neutron scattering at international large scale facilities provides us with a sensitive and versatile set of experimental tools, allowing the detailed investigation of atomic scale magnetic structure and dynamics.

We exploit neutron scattering facilities world-wide, but primarily conduct experiments at the Institut Laue-Langevin (ILL) in Grenoble, the SINQ spallation source at the Paul Scherrer Institute (PSI) in Switzerland and the BER-II research reactor at the Helmholtz Zentrum Berlin (HZB) in Germany. Our synchrotron x-ray experiments are mainly conducted at PETRA-III in Hamburg, Germany.

In-house experimental work

Laboratory for Mössbauer spectroscopy. Collaboration with DTU-CEN on electron microscopy studies. Investigations of bulk magnetic properties such as magnetic susceptibility and specific heat are performed in collaboration with DTU Energy and international collaborators. Work with companies In the project INDUCAT (link), funded by Innovationfund Denmark, we collaborate with Haldor Topsoe A/S, Sintex A/S, and the Danish Technological Institute.

We offer Mössbauer spectroscopy analyses to companies. Please contact Cathrine Frandsen for a quotation.

Derformation of Germanium crystals for neutron monochromators

Germanium crystals are in common use as monochromator crystals for neutron scattering instruments. We offer to perform deformation of germanium wafers, soldering of several such wafers to produce slabs, and finally cutting of these slabs into tiles that can be used as composite germanium monochromator crystals for neutron scattering instruments.

Please contact Niels Bech Christensen for more information

Magnetic phase diagram of LiCoPO4 determined by a combination of and magnetization measurements and neutron diffraction in magnetic fields up to 26T. Our neutron scattering data allow us to conclude that magnetoelectricity occurs when the magnetic propagation vector is Q=(0,0,0). From E. Fogh, R. Toft-Petersen, E. Ressouche, C. Niedermayer, S. L. Holm, M. Bartkowiak, O. Prokhnenko, S. Sloth, F. W. Isaksen, D. Vaknin, N. B. Christensen, Magnetic order, hysteresis, and phase coexistence in magnetoelectric LiCoPO₄, Physical Review B 96, 104420 (2017) https://journals.aps.org/prb/abstract/10.1103/PhysRevB.96.104420

Vortex phase diagram of superconducting vanadium determined by magnetization measurements and small angle neutron scattering. By probing directly the magnetic vortex correlations using neutrons, we were able to distinguish between a well-ordered lattice of vortices, and a disordered arrangement (vortex glass). The configuration of magnetic vortices is intimately connected to the critical current of the superconductor. From R. Toft-Petersen, A. B. Abrahamsen, S. Balog, L. Pocar, M. Laver, Decomposing the Bragg glass and the peak effect in a Type-II superconductor, Nature Communication 9, Article number 901 (2018) https://www.nature.com/articles/s41467-018-03267-z

Germanium wafer deformation in progress

Teaching activities

We organize/co-organize courses that relate to the scientific activities within magnetism and quantum materials.

• 10209: X-ray and Neutron Experiments at International Research Facilities (B.Sc. level)
• 10200: The structure and dynamics of materials studied with X-rays and neutrons (M.Sc. Level)
• 10314-10315: Magnetism and Magnetic Materials (M.Sc. Level)

Furthermore we are involved in the following courses within the Physics and Nanotechnology education at DTU:

• 10303: Condensed Matter Physics and Nanoscale Materials Physics (B.Sc. level)

Student projects

We offer student projects at all levels and always aim to integrate students as much as possible within our research activities.

Please contact us to hear more about the possibilities.