Spin and charge dynamics in [TbPc2]0 and [DyPc2]0 single-molecule magnets

Magnetization, ac-susceptibility, and muon spin-relaxation (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 [TbPc2](0) crystals show a high temperature nearly metallic behavior and a low-temperature-activated behavior.