ИСТИНА

Size effects and exchange interaction between band electrons (s,p) and d electrons localized on magnetic ions in diluted magnetic semiconductor (DMS) films lead to a band parameters changing, as a result of which the energy spectrum becomes very sensitive to the magnetic field and other external parameters, in particular of the sample size. As a result their physical characteristics: thermodynamic, kinetic and optical have a number of features. In this work the influence of energy spectrum parameters, magnetic impurities concentration, temperature and film thickness on the thermodynamic properties of diluted magnetic semiconductor films are studied. It has been shown that the specific heat capacity of degenerate electron gas in diluted semi-magnetic semiconductor films at low temperatures is greater than the heat capacity of non-magnetic structures. Excess heat capacity is due to an increase in the density of states and the magnetic properties of impurities. With increasing of the impurities concentration, the dependence of the heat capacity on temperature is non-monotonic. At very high concentrations x=0.8 this dependence has a maximum at T=20K. The appearance of the maximum is associated with the phase transition of the paramagnetic state to the antiferromagnetic state. It was found that for ultrathin diluted semi-magnetic semiconductor films the heat capacity is directly proportional to the band gap square, which increases with the concentration of the magnetic impurity. For example, when the concentration increases threefold, the band gap increases from 1.4 to 2.9 eV (for Cd1-xMnxTe). It was found that the heat capacity of a non-degenerate electron gas depends significantly on the exchange interaction energy. The entropy and heat capacity of diluted semi-magnetic semiconductor films are determined by the density of states, which depends on the impurities concentration, exchange interaction and film thickness. It is also noted that entropy and heat capacity oscillate with film thickness and when the Fermi energy coincides to the size-quantized level they experience a jump.