Title: Magnetic Resonance - Current State and Future Perspectives
Abstract: Magnetic resonance is a very dynamic phenomenon.Even when the spin system is at equilibrium, there is constant motion and relaxation.All too quickly anything we may do to the spin system is lost and forgotten.This limits what we are able to do with spins, whether it is measuring nanoscale distances with DEER/PELDOR spectroscopy, transferring dynamic nuclear polarization from near an electron spin to bulk nuclei, or making complex calculations with spin qubits.One major limitation is imposed in solids by the interaction of an unpaired electron spin with its nearby nuclear spin and the mutual interactions of the nuclear spins.Important but simple situations will be discussed.One is the phase memory relaxation of electron spins that limits resolution and sensitivity in echo-based measurements such as DEER/PELDOR, HYSCORE, and Pulse ENDOR.The dynamics of the nuclear spins often drives phase memory relaxation and also appears as spectral diffusion of the electron spins.However, the electron spin also affects the nuclear spin dynamics.One aspect of this is the so-called nuclear spin diffusion barrier that prevents efficient conduction of nuclear spin hyperpolarization generated at a free radical to the bulk nuclei.This barrier is evident in the magnetic resonance spectrum of the nearby nuclei, which are readily observed via ESEEM, HYSCORE and ENDOR spectroscopies.Fortunately, there are ways to change and perhaps control the spin system to obtain better resolution, longer distance measurements, slower relaxation, or a breach of the spin diffusion barrier.These include approaches such as echo refocusing, dynamic decoupling, isotopic editing, and changing spin multiplicity.Some examples will be shown.