To study non-Heisenberg effects in the vicinity of spin crossover in strongly correlated electron systems we derive an effective low-energy Hamiltonian for the two-band Kanamori model. It contains Heisenberg high-spin term proportional to exchange constant as well as low-spin term proportional to spin gap parameter εs. Using cluster mean field theory we obtain several non-Heisenberg effects. Near critical value of spin gap ε c s there is a magnetic phase transition of first order. In the vicinity of ε c s in the paramagnetic phase we observe non trivial behavior of the Curie constant in the paramagnetic susceptibility in the wide range of temperature. Reentrant temperature behavior of nearest-neighbor spin-spin correlations is observed at εs > ε c s . Finally, pressure-temperature magnetic phase diagram for ferroperriclase is obtained using the effective Hamiltonian.

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