Magnetic relaxations in a Tb-based single molecule magnet studied by quasielastic neutron scattering

- We examined a Tb based single molecule magnet by ac susceptibility and QENS.
- We found two distinct magnetic relaxations in a wide time range from 0.1 ms to 1 ps.
- The slower relaxation corresponds to the thermally activated tunneling process.
- The faster one couples with the motion of H atoms around the magnetic ions.
- The two relaxations exhibit a crossover around 100 ns.

By using ac magnetic susceptibility and quasielatic neutron scattering (QENS) techniques, we have investigated a magnetization relaxation phenomenon of a rare-earth based single molecule magnet, TbCuC19H20N3O16. We clearly identified and characterized two magnetic relaxations. The slower relaxation observed in the ac susceptibility is at the ms timescale around T=2 K and its activation energy is 16 K. On the other hand, the faster relaxation in the QENS measurements occurs on the timescale between ns and ps with activation energy of 174 K. The slower relaxation may occur through thermally activated tunneling among magnetic substates. We discuss two possible origins for the faster relaxation; one is a thermally activated tunneling between the higher excited states, the other is the magnetic relaxation coupled with the motion of ligands around the magnetic ions. This is the first clear observation of magnetic relaxation on the single molecule magnet revealed by QENS.