Short-range correlations in d-f cyanido-bridged assemblies with XY and XY-Heisenberg anisotropy

Two new d–f cyanido-bridged 1D assemblies [RE(pzam)3(H2O)Mo(CN)8]·H2O (RE = Sm(III), Er(III)) were synthesized and their magneto-structural properties have been studied by field-dependent magnetization and specific heat measurements at low temperatures (≥0.3 K). Below ≈ 10 K the ground state of both the Sm(III) and Er(III) ions is found to be a Kramers doublet with effective spin S = 1/2. From analyses of the low-temperature magnetic specific heat and magnetization the exchange coupling between these RE(III) effective spins and the Mo(V) spins S = 1/2 along the structural chains has been determined. It is found to be antiferromagnetic, with J∥/kB = −2.6 K and Ising–Heisenberg symmetry of the interaction (J∥/J⊥ = 0.3) for RE = Sm(III), whereas the compound with RE = Er(III) behaves as a pure XY chain, with J⊥/kB = −1.0 K. For the compound [Sm(pzam)3(H2O)Mo(CN)8]·H2O a small λ-type anomaly in the specific heat is observed at about 0.6 K, which is ascribed to a transition to long-range magnetic ordering induced by weak interchain interactions of dipolar origin. No evidence for 3D interchain magnetic ordering is found in the Er(III) analogue.