Permanent magnets have very good magnetic properties which can decrease because of low corrosion resistance and exposure to high temperatures. In diploma thesis we tested two hybrid materials: SrFe12O19/Sm2Fe17N3 bonded with PPS polymer and SrFe12O19/Nd2Fe14B bonded with PPS polymer. Firstly we made a microstructure analysis of powders that we used to make samples. From these powders we first made pellets. We used injection molding for making our samples. With step by step magnetizing and measuring the magnetic moment of our magnets, we made a saturation curve, which shows us the point of saturation. By testing our samples with permagraf we obtained demagnetizing curve from where we got the values of remanence, coercitivity and maximal energy product. With three-point flexure test, we tested the strength of our specimens. The main test in the diploma work was stability of magnetic charactheristics in different medias. We observed how the magnetic moment of our magnets and the magnetic flux of rotors change.