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The influence of the kinematic interaction and the indirect exchange of electrons on the magnetic structure of a narrow-gap Hubbard magnet is investigated using the diagram technique of the perturbation theory. The summation of an infinite series of like diagrams makes it possible to separate the effective self-consistent filed. In contrast to the previous studies, the proposed theory contains only two self-consistent parameters, i.e., the chemical potential and the average spin. The obtained system of equations for these parameters admits the analytical solution at zero temperature. The competition of the simplest kinematic contribution and the indirect antiferromagnetic exchange is clearly demonstrated using the concentration dependences of the Neel temperature as an example. The boundaries of the existence of the homogeneous ferromagnetic, antiferromagnetic, and paramagnetic phases as a function of the electron concentration and the indirect exchange parameter are determined by numerically analyzing the internal energy.

The magnetic and transport properties of La1−xMn1+xO3 manganites with excess manganese are studied. It is shown that magnetic and charge ordering heavily depends on the superstoichiometric manganese content, magnetic field, and pressure. The magnetoresistive effect (MRE) is enhanced as the manganese concentration increases. In addition to the paramagnet-ferromagnet transition, the temperature dependences of the magnetization exhibit anomalies at low temperatures in samples with x=0.1–0.4. The magnetization decreases at T

The results of measuring the temperature and field dependences of the magnetization of a RbDy(WO4)2 single crystal in the temperature range from 4.2 to 50 K and in magnetic fields up to 1.6 T are presented. The energies of the exchange and dipole-dipole interactions are estimated. The magnetic structure of the ground state is determined.