THEORY OF THE MAGNETIC-PROPERTIES OF ISOTROPIC LADDER-TYPE DOUBLE CHAINS WITH CLASSICAL SPINS AT THE BUNCH-UPRIGHT INTERSECTIONS - APPLICATION TO GD(III)-CU(II) COMPOUNDS

A general method is proposed for computing the susceptibility of a lar ge category of regular magnetic double chains in which more or less co mplex quantum spin systems, occupying the uprights and the bunches, ar e linked through the nodes by magnetic cations. Only two conditions ar e required: (i) the magnetic cations at the intersections of the uprig hts and the bunches must exhibit large enough spin quantum numbers to allow a classical treatment and (ii) the overall zero-field Hamiltonia n must be isotropic. The main applications of the model are listed. Mo re specifically, results are given for the case where the quantum spin systems are empty, and the neighboring classical spins directly inter act through Heisenberg exchange. The model is also used with particula r success to interpret the observed magnetic properties of the compoun d Gd-2(ox)[Cu(pba)](3)[Cu(H2O)5].20H(2)O, which enters the general fra mework, with each quantum system reducing to a single 1/2 spin. It is also applied tentatively to the related compound Gd-2[Cu(pba)]3.23H(2) O.