Spin and charge dynamics in [TbPc$_2$]$^0$ and [DyPc$_2$]$^0$ single molecule magnets

TL;DR

This study investigates the spin and charge dynamics in neutral lanthanide phthalocyanine single molecule magnets using various techniques, revealing high-temperature thermally activated regimes and low-temperature tunneling behaviors with discrepancies between microscopic and macroscopic measurements.

Contribution

It provides a comparative analysis of spin dynamics in [LnPc$_2$]^0 molecules using AC susceptibility and μSR, highlighting differences in tunneling regimes and charge transport properties.

Findings

High-temperature thermally activated spin dynamics observed.

Discrepancies between μSR and AC susceptibility in tunneling regime.

Resistivity shows metallic behavior at high T and activated behavior at low T.

Abstract

Magnetization, AC susceptibility and $\mu$SR measurements have been performed in neutral phthalocyaninato lanthanide ([LnPc$_2]^0$) single molecule magnets in order to determine the low-energy levels structure and to compare the low-frequency spin excitations probed by means of macroscopic techniques, such as AC susceptibility, with the ones explored by means of techniques of microscopic character, such as $\mu$SR. Both techniques show a high temperature thermally activated regime for the spin dynamics and a low temperature tunneling one. While in the activated regime the correlation times for the spin fluctuations estimated by AC susceptibility and $\mu$SR basically agree, clear discrepancies are found in the tunneling regime. In particular, $\mu$SR probes a faster dynamics with respect to AC susceptibility. It is argued that the tunneling dynamics probed by $\mu$SR involves fluctuations which do not yield a net change in the macroscopic magnetization probed by AC susceptibiliy. Finally resistivity measurements in [TbPc$_2]^0$ crystals show a high temperature nearly metallic behaviour and a low temperature activated behaviour.