Nanolamellar structure obtained by simple crystallization of an amorphous cobalt-based magnetic alloy

A novel modulated nanolamellar structure with a lamellar spacing of about 5 nm was obtained by simple heat treatment of an initially amorphous Co₆₅Si₁₅B₁₄Fe₄Ni₂ magnetic alloy. The crystallographic characteristics of this nanolamellar structure were investigated using selected area diffraction pattern, Kikuchi maps, convergent beam electron diffraction, and X-ray diffraction techniques. The crystal structure of the lamellae was found to be a novel phase with a C-base centered orthorhombic crystal structure of a=0.74 nm, b=1.07 nm, and c=0.77 nm, the nanolamellar structure was modulated along the (0 0 1) plane. High-resolution transmission electron microscopy observations showed negligible lattice mismatch between neighboring lamellae. Electron energy loss spectroscopy mapping showed a periodic variation of boron composition corresponding to the nanolamellar periodicity. The formation of the nanolamellar structure was found to be due to spinodal decomposition within the grains formed by crystallization of the alloy.