The monograph considers the main state and thermodynamics of antiferromagnets, a spin liquid with a four-spin interaction in low-dimensional semiconductors. The spectrum of spin-polaron excitations, thermo. Eds, electrical resistance and magnetoresistance when the magnetic structure changes within the sd-model. The role of strong electron correlations and interaction of electrons with the lattice on the orbital ordering of electrons, magnetic phase transitions in ions with threefold degeneration. The influence of quantum fluctuations on the magnetic structure during orbital ordering is determined, leading to different topology of exchange interactions. Microscopic mechanism of magnetoelectric and magnetic properties in manganese sulfides with cobalt. This monograph will be useful to undergraduate physicists, graduate students in the specialty, researchers and faculty .