Tm(III) complexes undergoing slow relaxation of magnetization: exchange coupling and aging effects

The present study focuses on the dynamical magnetic behaviour of exchange coupled 3d-4f complexes containing the scarcely considered non Kramers Tm3+ center, the 3d metal ions being either the low-spin Fe3+ (1) or the diamagnetic Co3+ (2) ion. Both complexes display field-dependent slow relaxation of magnetization. The field and temperature dependences of the relaxation rate provided indication of relevant contributions from quantum tunnelling, direct and Raman processes, with only minor effects from exchange coupling interactions. Furthermore, aged sample of 2 exhibited additional relaxation process, possibly due to solvent loss, highlighting the importance of a careful consideration of this factor when analysing the magnetization dynamics in solvated systems