FLEET research seminar: Magneto-optical polarisation spectroscopy with synchrotron radiation on graphene

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22 August 2017 at 3:00 am – 22 August 2017 at 3:00 pm
G29 New Horizons Centre, 20 Research Way
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Engineering; Information Technology; Science; Seminars & Workshops


Discover synchrotron methods for characterising graphene from the University of Applied Sciences Muenster.

Polarisation spectroscopy with synchrotron radiation is a powerful tool for both, the investigation of structural and magnetic order in bulk material and two-dimensional systems. After giving an experimental review on polarisation detectors for synchrotron radiation the application to non-magnetic as well as to magneto-optical effects as Faraday, Kerr, Voigt and the X-Ray Circular Dichroism (XMCD) are presented [1, 2].

The existence of natural birefringence in x-ray reflection on graphene is demonstrated at energies spanning the carbon 1s absorption edge. This new x-ray effect has been discovered with precision measurements of the polarization-plane rotation and the polarization-ellipticity changes that occur upon reflection of linearly polarized synchrotron radiation on monolayer graphene. Extraordinarily large polarization-plane rotations of up to 30°, accompanied by a change from linearly to circularly polarized radiation have been measured for graphene [3].

The existence of a giant magneto-optical Faraday-effect at the carbon 1s edge of single-layer graphene on Co is demonstrated [4]. Exploiting resonant enhancement at the carbon 1s and at the cobalt 2p edges element-selective magnetic hysteresis curves can be monitored showing ferromagnetic order in graphene. The magnetism in graphene is found to be carried by and be strongly enhanced by aligned π-orbitals of carbon atoms that have a magnetic moment of 0.14mB deduced from XMCD and transversal magneto-optical Kerr effect (T-MOKE) spectra. The magnetism of graphene is induced by hybridization with the Co 3d orbitals where the position of carbon atoms of sublattice A or B plays a role. We show experimentally that the related reduction of A-B-symmetry leads to a splitting of the spin polarized density of conduction band states which is responsible for the strong magneto-optical Faraday effect.

Prof. Hans-Christoph Mertins is a professor of physics at the University of Applied Sciences Muenster since 2003. Prior to this, he was a scientist at the large scale facility Berliner Elektronenspeicherring Gesellschaft für Synchrotronstrahlung mbH (BESSY) and working on the European Community TMR-LSF RTD Projects.

He was involved in the development of beamlines for synchrotron radiation and his research interests are on nano-structured multilayer systems and nano-materials for magnetic sensors, development and characterisation of X-ray mirrors and polarisation-detectors. Prof. Mertins also holds a patent for a polarization modulator for X-rays.

Dianne Ruka
FLEET: ARC Centre of Excellence in Future Low-Energy Electronics Technologies