Toroidal magnetic cores are made of a Fe-based thin (20 microns) nanocrystalline ribbon and have low loss, high induction of saturation, high operating temperature (up to 150 C), high magnetic permeability. Magnetic cores have a negative temperature coefficient of losses that provides stabilization mode transformer temperature. Application in power high- frequency transformers push-pull,bicyclic SMPS, DC-DC converters, audiotransformers. High permeability provides good electromagnetic connection of windings and low leakage inductance values. HIGHLIGHTS OF THE MATERIAL: Induction amplitude, Bm (25 C) 1,2 T Induction amplitude, Bm (90 C) 1,1 T Curie temperature, Tc 570 C Magnetostriction less than 0,5 x10 ^ -6 Magnetic Permeability (100 kHz) - up to 20,000