EXCHANGE INTERACTIONS IN LANTHANIDE BINUCLEAR COMPOUNDS - THE CUBIC ISOTROPIC CASE

Following the idea of Lines a combined model for the description of exchange interactions in binuclear lanthanide compounds is proposed. Susceptibility expressions for lanthanide centres with an odd number of f electrons are developed assuming cubic ligand fields and isotropic exchange interactions. The latter are taken into consideration as a molecular field in the excited single-ion levels, but treated with greater accuracy using the Heisenberg model within the single-ion ground states. Model calculations on the basis of an antiferromagnetic coupling within the dimers show that temperatures where magnetic susceptibilities reach their maximum, T(χmax), vary widely when total spin S of the lanthanide is altered. The highest T(χmax) should be expected in the case of Gd3+ (4f7), Sm3+ (4f5) and Dy3+ (4f9). This is confirmed by experimental results so far obtained regarding binuclear complexes [Ln(C5H5)2Br]2 (Ln = Gd, Dy, Er and Yb). © 1990.