Anisotropy of Spin–Lattice Relaxations in Mononuclear Tb3+ Single-Molecule Magnets

Through the use of a new homemade probe, the angular dependences of the dc and ac susceptibilities of single crystals of [Tb3+(ZnL)2]­CF3SO3 (H3L denotes a tripodal hexadentate Schiff base ligand) were investigated for the purpose of resolving the anisotropic magnetic relaxation at low temperatures (down to 2 K). The dc magnetic measurements and crystal field calculations have confirmed a strong uniaxial anisotropy with an easy axis along the C3 axis, which passes through the Zn-Tb-Zn array. The ac data demonstrate that the magnetic relaxations crucially depend on the angle between the easy axis and the direction of applied magnetic field, and this type of definitive identification is not possible in works using randomly arranged microcrystals or powder. The theoretical analysis shows that the anisotropy of the dynamical properties is a manifestation of a quantum structure, in particular, the angle dependence of the distribution of electronic levels. More specifically, the angle dependences of the energies of the two lowest levels of the Tb3+ ion in 1 kOe were obtained.