Magnetic interactions in Fe-Zr-B-Cu nanocrystalline materials at elevated temperatures

Nanocrystalline samples were obtained by subsequent annealing of the ${\mathrm{Fe}}_{93\mathrm{-}\mathit{x}\mathrm{-}\mathit{y}}$ ${\mathrm{Zr}}_7$ ${\mathrm{B}}_{\mathit{x}}$ ${\mathrm{Cu}}_{\mathit{y}}$ metallic glass ribbons either in a conventional furnace or by electric current flowing through the ribbon. The coercive field of the slightly crystallized material shows a drastic increase at temperatures about the Curie point of the amorphous matrix, whereas for samples with high content of the crystalline phase the coercivity increases slowly in the temperature range well above ${\mathit{T}}_{\mathit{C}}$. Temperature dependencies of the coercive field show that at elevated temperatures the magnetic interactions between ferromagnetic particles, most probably of exchange origin, take place through the paramagnetic intergranular matrix.