Nanogranular Phase Formation During Devitrification of Fe(NiCo)ZrB Amorphous Alloys

Abstract

A comprehensive review of our recent experimental and theoretical developments in the processing of nanocrystalline soft magnetic materials made by crystallization of amorphous precursors and containing new nanocrystalline phases is given. The relationship between the structures of the metastable and equilibrium phases and their transformations are discussed. Nickel-rich amorphous precursors with stoichiometry Ni64Fe16Zr7B12Au1 were produced by melt-spinning technique and then heat-treated at temperatures ranged from 420 °C to 600 °C for one hour to form nanostructured alloy. The transformation from the amorphous state into the nanocrystalline state was investigated by the differential scanning calorimetry (DSC), the x-ray diffraction (XRD), the vibrating sample magnetometry (VSM) and Mossbauer techniques. The annealing favours the emergence of cubic FexNi23-xB6 crystalline grains (10-25 nm in diameter). Magnetic measurements made at 4.2-1100 K reveal rather high value of saturation magnetization (nearly 60 and 40 Am2/kg at 4.2 K and room temperature, respectively) in amorphous as well as in nanocrystalline states. These facts are consistent with 300 K 57Fe Mossbauer results which are well supported by the calculations of Ni and Fe magnetic moments in Ni23B6 and Fe23B6 phases, using the spin polarized tight binding linear muffin-tin orbital (TB-LMTO) method. However, anomalous high magnetic moments of Fe and Co atoms were found in some inequivalent positions in the crystal structure.