FEL-based pulsed-field ESR technique: recent developments at the Dresden High Magnetic Field Laboratory

The successful use of picosecond-pulse free-electron-laser (FEL) radiation for the continuous-wave THz-range electron spin resonance (ESR) spectroscopy has been demonstrated. The unique combination of two linac-based FELs [1] (covering the wavelength range of 4 - 250 μm) with high magnetic fields at the Research Center Dresden-Rossendorf (FZD) allows for tunable-frequency ESR spectroscopy in a frequency range of 1.2 - 75 THz in magnetic fields up to ~ 70 T with a spectral resolution better than 1% [2]. The new approach is of particular importance for studying magnetic excitations in spin systems with a large zero-field splitting and materials exhibiting field-induced phenomena. The performance of the spectrometer is illustrated with ESR spectra obtained in the low-dimensional organic material (C6H9N2)CuCl3 and the multiferroic compound YMnO3††.