Discovery of a Dysprosium Metallocene Single-Molecule Magnet with Two High-Temperature Orbach Processes

Magnetic bistability
in single-molecule magnets (SMMs) is a potential
basis for new types of nanoscale information storage material. The
standard model for thermally activated relaxation of the magnetization
in SMMs is based on the occurrence of a single Orbach process. Here,
we show that incorporating a phosphorus atom into the framework of
the dysprosium metallocene [(CpiPr5)­Dy­(CpPEt4)]+[B­(C6F5)4]− (CpiPr5 is penta-isopropylcyclopentadienyl,
CpPEt4 is tetraethylphospholyl) leads to the occurrence
of two distinct high-temperature Orbach processes, with energy barriers
of 1410(10) and 747(7) cm–1, respectively. These
barriers provide experimental evidence for two different spin–phonon
coupling regimes, which we explain with the aid of ab initio calculations.
The strong and highly axial crystal field in this SMM also allows
magnetic hysteresis to be observed up to 70 K, using a scan rate of
25 Oe s–1. In characterizing this SMM, we show that
a conventional Debye model and consideration of rotational contributions
to the spin–phonon interaction are insufficient to explain
the observed phenomena.