Scientific Highlights LSM

20 July 2018

Collective magnetism in an artificial 2D XY spin system

Two-dimensional magnetic systems with continuous spin degrees of freedom exhibit a rich spectrum of thermal behaviour due to the strong competition between fluctuations and correlations. When such systems incorporate coupling via the anisotropic dipolar interaction, a discrete symmetry emerges, which can be spontaneously broken leading to a low-temperature ordered phase. However, the experimental realisation of such two-dimensional spin systems in crystalline materials is difficult since the dipolar coupling is usually much weaker than the exchange interaction. Here we realise two-dimensional magnetostatically coupled XY spin systems with nanoscale thermally active magnetic discs placed on square lattices. Using low-energy muon-spin relaxation and soft X-ray scattering, we observe correlated dynamics at the critical temperature and the emergence of static long-range order at low temperatures, which is compatible with theoretical predictions for dipolar-coupled XY spin systems. Furthermore, by modifying the sample design, we demonstrate the possibility to tune the collective magnetic behaviour in thermally active artificial spin systems with continuous degrees of freedom.
Facility: SμS, SLS

Reference: N. Leo et al, Nature Communications 9, 2850 (2018)

Read full article: here

24 May 2018


ETH Medal for outstanding MSc thesis: Beam Characterization of Low Energy Electrons from a Laser Wakefield Accelerator by N. Sauerwein

Large Research Facilities

The characteristics of low energy electrons accelerated by a laser wakefield (Laser Wakefield Acceleration LWFA) has been studied. The work included understanding the acceleration process, setting up the experiment and measuring properties like charge, divergence and energy of the accelerated electrons. The experiment included diagnostics for the laser and the electrons. In order to make high-resolution energy distribution measurements with relative errors ∆E/E of below 10%, a tunable electron spectrometer has been designed, built and characterized. A tunable permanent magnet quadrupole triplet has been designed for stigmatic focusing in a range of 5 keV to 5 MeV. The thesis can be found here: MSc Thesis N. Sauerwein