Low-energy excitations in electron-doped metal phthalocyanine from NMR in Li$_{0.5}$MnPc

TL;DR

This study uses NMR and magnetization measurements to investigate low-energy excitations in electron-doped metal phthalocyanine, revealing two distinct low-frequency dynamics related to spin freezing and electron hopping.

Contribution

It provides the first detailed analysis of low-energy excitations in Li-doped MnPc, highlighting two different dynamic processes and their relation to disorder and electron correlations.

Findings

Identification of slow spin freezing dynamics at low temperatures.

Observation of electron hopping along Li-rich chains.

Analysis of correlation times and disorder effects.

Abstract

$^7$Li and $^1$H NMR and magnetization measurements in \lpc (Pc$\equiv$C$_{32}$H$_{16}$N$_8$), recently proposed as a strongly correlated metal, are presented. Two different low-frequency dynamics are evidenced. The first one, probed by $^1$H nuclei gives rise to a slowly relaxing magnetization at low temperature and is associated with the freezing of MnPc $S=3/2$ spins. This dynamic is similar to the one observed in pristine $\beta$-MnPc and originates from Li depleted chain segments. The second one, evidenced by $^7$Li spin-lattice relaxation rate, is associated with the hopping of the electrons along Li-rich chains. The characteristic correlation times for the two dynamics are derived and the role of disorder is briefly discussed.