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Abstract The Hubbard model in the strong coupling limit is used to study the behaviour of substances containing ions with orbitally degenerate ground state (Jahn‐Teller ions) in a magnetic field. In such substances the orbital occupancy and the magnetic structure appear to be closely connected. It is shown that in these systems a transition of first order may occur between different anti‐ferromagnetic phases as well as jumplike spin‐flip transitions (even for an isotropic exchange interaction S i S j ). The field dependence of the magnetic moment may be nonlinear, typical of meta‐magnetic substances. Both a simple model problem and a specific case of pervoskites with Jahn‐Teller ions (such as KCuF 3 ) are studied. The behaviour of quasi one dimensional systems is also considered.
Khomskiǐ et al. (Tue,) studied this question.