Exchange Interactions between Pairs of Differing Magnetic Spins in Heteropoly Complexes

Abstract
Coupled pairs of differing magnetic spins in tungsto-heteropoly complexes have been investigated by studying the magnetic susceptibility over the temperature range 2–300°K. The two sites of the magnetic ions are surrounded by oxygen ions in octahedral and tetrahedral coordinations with one oxygen ion in common. The ions studied were Co2+, Co3+, and Fe3+ in a total of six combinations on the two sites, offering a unique set of symmetries and ions for examining super-exchange effects. A closed form for the susceptibility has been obtained on assuming the spin Hamiltonian H=β (g1S1+g2S2)· H-JS1· S2, allowing for the possibility of g1≠ g2, S1≠ S2. Fitted values of J/k range from −6 to −70°K depending on the combinations of ions. The experimental agreement with the spin Hamiltonian for all cases studied is satisfactory for this system.

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