Exchange effects in a two-dimensional electron gas in a semiconductor at finite temperatures

The exchange energy of electrons of the size quantization subzone in a narrow quantum well has been calculated at arbitrary electron concentrations and temperatures. Conditions have been determined for the transition of a two-dimensional electron system into a spin-polarized state owing to the gain in the exchange contribution to a free energy. It has been demonstrated that in a certain electron concentration region two transitions, first into a polarized and then into an unpolarized state, can consecutively take place under changes of temperature.