  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 $\varepsilon_s$. Using cluster mean field theory we obtain several
non-Heisenberg effects. Near critical value of spin gap $\varepsilon^c_s$ there
is a magnetic phase transition of first order. In the vicinity of
$\varepsilon^c_s$ 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 $\varepsilon_s > \varepsilon^c_s$. Finally,
pressure-temperature magnetic phase diagram for ferroperriclase is obtained
using the effective Hamiltonian.
