Magnetic resonance provides a unique window into quantum spin systems, revealing both their microscopic structure and their dynamical behavior. In particular, pulsed electron–nuclear double resonance (ENDOR) probes hyperfine interactions between electron and nuclear spins, enabling structural measurements at the nanometer scale while simultaneously providing access to spin relaxation and coherence phenomena.
In this talk, I will discuss recent advances in ENDOR spectroscopy of coupled 19F-Gd(III) spin systems, where the large magnetic moment and high-spin nature (S=7/2) of gadolinium create new opportunities both for structural characterization and spin manipulation. We show that high magnetic fields and low temperatures unlock an unexpected orientational selectivity, allowing three-dimensional structural information to be extracted from disordered samples. Despite substantial distributions of local ligand fields around the gadolinium ions, the underlying anisotropy axes remain remarkably well defined, providing access to structural details that extend beyond simple distance measurements.
Beyond structure determination, these systems offer a versatile platform for studying coupled electron–nuclear spin dynamics. I will demonstrate how coherent control experiments reveal relaxation processes of hyperfine-coupled nuclei and how frequency-multiplexed approaches can substantially enhance the sensitivity of ENDOR spectroscopy.