Spin dynamics in rare earth single molecule magnets from muSR and NMR in [TbPc$_{2}$]$^{0}$ and [DyPc$_{2}$]$^{0}$

TL;DR

This study investigates the spin dynamics of [TbPc2]0 and [DyPc2]0 single molecule magnets using muon and NMR techniques, revealing slow spin fluctuations and distinct high-temperature activated regimes.

Contribution

It provides new insights into the spin fluctuation timescales and regimes in lanthanide-based single molecule magnets, highlighting differences between Tb and Dy complexes.

Findings

Correlation time for spin fluctuations ~0.1 ms at 50 K

Two fluctuation regimes in [TbPc2]0: activated and quantum

High-temperature activated dynamics in [DyPc2]0 not explained by a single spin-phonon coupling

Abstract

The spin dynamics in [TbPc$_{2}$]$^{0}$ and [DyPc$_{2}$]$^{0}$ single molecule magnets have been investigated by means of muon and nuclear spin-lattice relaxation rate measurements. The correlation time for the spin fluctuations was found to be close to 0.1 ms already at 50 K, about two orders of magnitude larger than the one previously found in other lanthanide based single molecule magnets. In [TbPc$_{2}$]$^{0}$ two different regimes for the spin fluctuations have been evidenced: a high temperature activated one involving spin fluctuations across a barrier $\Delta\simeq 880 K$ separating the ground and first excited states and a low temperature regime involving quantum fluctuations within the twofold degenerate ground-state. In [DyPc$_{2}$]$^{0}$ a high temperature activated spin dynamics is also evidenced which, however, cannot be explained in terms of a single spin-phonon coupling constant.