Superparamagnetic Relaxation in Nanocrystalline Fe80Zr7B12Cu1 Alloys

Nanocrystalline Fe₈₀Zr₇B₁₂Cu₁ alloys with different amounts and sizes of bcc precipitates were prepared by appropriate annealing of amorphous ribbons. The 6–10 nm ferromagnetic bcc granules are embedded in a residual amorphous tissue with a thickness at least 4 nm. Above room temperature superparamagnetic relaxation characteristic for small magnetic particles was observed with increasing temperature, as indicated by a significant increase in the width of the Mössbauer lines belonging to the bcc precipitates. It shows the absence of magnetic coupling which is stronger than the dipole-dipole interaction between the ferromagnetic nanoparticles.