Spin-Phonon Relaxation in Magnetic Molecules: Theory, Predictions and Insights

Abstract

Magnetic molecules have played a central role in the development of magnetism and coordination chemistry and their study keeps leading innovation in cutting-edge scientific fields such as magnetic resonance, magnetism, spintronics, and quantum technologies. Crucially, a long spin lifetime well above cryogenic temperature is a stringent requirement for all these applications. In this chapter we review the foundations of spin relaxation theory and provide a detailed overview of first-principles strategies applied to the problem of spin-phonon relaxation in magnetic molecules. Firstly, we present a rigorous formalism of spin-phonon relaxation based on open quantum systems theory. These results are then used to derive classical phenomenological relations based on the Debye model. Finally, we provide a prescription of how to map the relaxation formalism onto existing electronic structure methods to obtain a quantitative picture of spin-phonon relaxation. Examples from the literature, including both transition metals and lanthanides compounds, will be discussed in order to illustrate how Direct, Orbach and Raman relaxation mechanisms can affect spin dynamics for this class of compounds.

Unravelling the role of spin–vibrational coupling in designing high-performance pentagonal bipyramidal Dy(iii) single ion magnets

“…53 On the other hand, Lunghi and co-workers recently demonstrated the role of anharmonic phonons in dictating the under-barrier magnetisation relaxation. [1][2][3][4]49,52,[85][86][87] Therefore, spin-phonon coupling calculations are of utmost importance to unveil the underlying physical process of magnetisation relaxation and provide a clear indication of how the relaxation process is linked with molecular motions. As a result, it can provide the design criteria for potential SMMs with chemical tuning to quench the vibrations associated with Orbach and Raman relaxation processes.…”

Molecular nanomagnets: a viable path toward quantum information processing?

“…The coupling to spins occurs through the modulation of the different spin-Hamiltonian parameters (anisotropy, exchange, or even hyperfine interactions). Various different phonon types (acoustical or optical) and processes (direct, Orbach, Raman) can play a role, their relative importance depending on the specific MNM, on the structure of the phonons, and on the temperature range [7,60,61,74,77,[112][113][114][115][116]. The rate of direct and Orbach processes strongly depends on the structure of the molecular energy spectrum.…”

PyrroTriPol: a semi-rigid trityl-nitroxide for high field dynamic nuclear polarization

“…smaller spin-orbit coupling, their relaxation times are longer. 64,66,67 The narrower linewidth also implies that the mw rotor events are more efficient when irradiating the narrow line radical. 36 In addition, for a given magnetic eld, MAS frequency and e-e couplings, CE and dipolar-J rotor events are favored thanks to the presence of the narrow line radical.…”