Hetero-tri-spin [2p-3d-4f] chain compounds based on nitronyl nitroxide lanthanide metallo-ligands: synthesis, structure, and magnetic properties.

Employing nitronyl nitroxide lanthanide(III) complexes as metallo-ligands allowed the efficient and highly selective preparation of three series of unprecedented hetero-tri-spin (Cu-Ln-radical) one-dimensional compounds. These 2p-3d-4f spin systems, namely [Ln3Cu(hfac)11(NitPhOAll)4] (Ln(III) = Gd 1Gd, Tb 1Tb, Dy 1Dy; NitPhOAll = 2-(4'-allyloxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), [Ln3Cu(hfac)11(NitPhOPr)4] (Ln(III) = Gd 2Gd, Tb 2Tb, Dy 2Dy, Ho 2Ho, Yb 2Yb; NitPhOPr = 2-(4'-propoxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide) and [Ln3Cu(hfac)11(NitPhOBz)4] (Ln(III) = Gd 3Gd, Tb 3Tb, Dy 3Dy; NitPhOBz=2-(4'-benzyloxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide) involve O-bound nitronyl nitroxide radicals as bridging ligands in chain structures with a [Cu-Nit-Ln-Nit-Ln-Nit-Ln-Nit] repeating unit. The dc magnetic studies show that ferromagnetic metal-radical interactions take place in these hetero-tri-spin chain complexes, these and the next-neighbor interactions have been quantified for the Gd derivatives. Complexes 1Tb and 2Tb exhibit frequency dependence of ac magnetic susceptibilities, indicating single-chain magnet behavior.

Studies on a frustrated Heisenberg spin chain with alternating ferromagnetic and antiferromagnetic exchanges.

We study Heisenberg spin-1/2 and spin-1 chains with alternating ferromagnetic (J(F)(1)) and antiferromagnetic (J(A)(1)) nearest-neighbor interactions and a ferromagnetic next-nearest-neighbor interaction (J(F)(2)). In this model frustration is present due to the non-zero J(F)(2). The model with site spin s behaves like a Haldane spin chain, with site spin 2s in the limit of vanishing J(F)(2)and large J(F)(1)/J(A)(1). We show that the exact ground state of the model can be found along a line in the parameter space. For fixed J(F)(1), the phase diagram in the space of J(A)(1)-J(F)(2) is determined using numerical techniques complemented by analytical calculations. A number of quantities, including the structure factor, energy gap, entanglement entropy and zero temperature magnetization, are studied to understand the complete phase diagram. An interesting and potentially important feature of this model is that it can exhibit a macroscopic magnetization jump in the presence of a magnetic field; we study this using an effective Hamiltonian.