Field-induced magnetic relaxation in heteropolynuclear LnIII/ZnII metal organic frameworks: cerium and dysprosium cases

Abstract

This study focuses on investigating the magnetic properties of the Ce^III-based metal–organic framework [Ce₂Zn₃(oda)₆(H₂O)₆]·12H₂O (1), along with the hexagonal and cubic phases of the analog compound [Dy₂Zn₃(oda)₆(H₂O)₆]·xH₂O (2a with x = 16 and 2b with x = 3, respectively). Dynamic magnetic measurements reveal field-induced slow relaxation of magnetization in all of the compounds. Magnetic relaxation for 1 under an external field of 1 kOe can be described by the power law τ⁻¹ ∝ T^2.6(3), suggesting spin relaxation through a phonon-bottleneck non-ideal Raman process. The absence of an Orbach-type relaxation mechanism is explained through ab initio calculations, which also show that the coordination geometry around Ce^III leads to strong mixing of spin–orbit levels in the ground state. This mixing enables significant tunneling probability, and is responsible of the absence of magnetic relaxation without an applied magnetic field. In contrast, 2a and 2b exhibit a more complex dynamic behavior with two distinct relaxation channels at different frequencies. However, despite minor structural differences their magnetic properties are qualitatively similar.