Abstract
We present a study of ferromagnetic systems based on Fe-Co-Sn-B in nanocrystalline state. Interesting magnetic properties potentially are given by the homogeneous and ultrafine structure of bcc Fe grains in amorphous structure. The effect of alloying by Sn improves the properties of resulting structure constituted be crystalline grains in amorphous matrix. The structure transformation from amorphous state was investigated by selected techniques of thermal analysis and the resulting phase and morphology of crystalline products were analyzed.