Nuclear magnetic resonance study of the crystallization kinetics in soft magnetic nanocrystalline materials

We used the nuclear magnetic resonance technique to study the evolution of the structural and magnetic properties of Fe-based melt-spun ribbons of Fe73.5Cu1Nb3Si13.5B9, Fe73.5Cu1Nb3Si18.5B4, and Fe86Zr7Cu1B6, as-cast and annealed at 500, 540, and 430 °C, respectively. Experiments were carried out at 4.2 K and zero-applied magnetic field, and in a controlled radio-frequency (rf) field. This type of measurement allows us to observe B and Nb sites, and makes it possible to distinguish signals associated with regions of different magnetic hardnesses. The results exhibit a high dependence of the spectra on rf power. For Fe–Si-based alloys, we observe well-defined Nb93 resonance signals from three distinct sites according to the concentration of Fe atoms in their neighborhood. In the Fe73.5Cu1Nb3Si18.5B4 spectra we also observe a peak around 34 MHz, connected to the B11 resonance in different Fe–B compounds, which remains as the rf power decreases, suggesting that the signals come from atoms inside a soft magnetic region. As for the Fe–Zr alloy, we also observe a peak around 36 MHz, identified as the B11 resonance, and a broad line around 62 MHz.