Theoretical Study of Exchange Coupling in 3d-Gd Complexes: Large Magnetocaloric Effect Systems

Abstract

Polynuclear 3d transition metal-Gd complexes are good candidates to present large magnetocaloric effect. This effect is favored by the presence of weak ferromagnetic exchange interactions that have been investigated using methods based on Density Functional Theory. The first part of the study is devoted to dinuclear complexes, focusing on the nature and mechanism of such exchange interactions. The presence of two bridging ligands is found more favorable for ferromagnetic coupling than a triple-bridged assembly, especially for complexes with small M-O···O-Gd hinge angles. Our results show the crucial role of the Gd 5d orbitals in the exchange interaction while the 6s orbital seems to have a negligible participation. The analysis of the atomic and orbital spin populations reveals that the presence of spin density in the Gd 5d orbital is mainly due to a spin polarization effect, while a delocalization mechanism from the 3d orbitals of the transition metal can be ruled out. We propose a numerical DFT approach using pseudopotentials to calculate the exchange coupling constants in four polynuclear first-row transition metal-Gd complexes. Despite the complexity of the studied systems, the numerical approach gives coupling constants in excellent agreement with the available experimental data and, in conjunction with exact diagonalization methods (or Monte Carlo simulations), it makes it possible to obtain theoretical estimates of the entropy change due to the magnetization/demagnetization process of the molecule.

Metal-radical coordination complexes of thiazyl and selenazyl ligands

“…The 6s orbitals, being spherical, cannot be solely responsible for FM exchange coupling, owing to symmetry. Thus, it is reasonable to conclude that the 5f orbitals must be involved, and this finding is in keeping with recent computational analysis of exchange coupling in related binuclear 3d metal-Gd III complexes [86]. M a n u s c r i p t Figure 14.…”

A ferromagnetically coupled diphenoxo-bridged Gd3+–Mn2+ dinuclear complex with a large magneto-caloric effect

“…7,8 From heat capacity measurements, we found that the magnetic entropy change reaches significant values for 1-3 K, namely DS m = 23.5 J kg À1 K À1 for DB = 7 T. Our results therefore suggest that the Gd…”

Can novel dinuclear Ni–Gd complexes give supplementary information on the Ni–Gd magnetic interaction?

“…Recently, a theoretical study of exchange coupling in 3d-Gd complexes appeared in the literature [34]. The authors demonstrate that the presence of the 5d Gd functions in their basis set is necessary to properly reproduce the experimental J values.…”