The influence of growth impurities (oxygen and carbon) on the thermalsdefect formation in silicon single crystals has been studied. Annealing was carried out in the temperature range 700-1100°C in steps of 50°C for 5 hours at each temperature. The magnetic, micromechanical and structural properties of annealed silicon single crystals have been experimentally studied. The distribution of defects formed at different annealing temperatures has been studied. The correlation between changes of magnetic susceptibility, microhardness and rearrangement of structural defects in crystals after their heat treatment is revealed. Concentrations and sizes of magnetically ordered clusters are estimated. Interpretation of the obtained experimental results is offered.