Tailoring soft and hard magnets by annealing Co-based metallic glass

Co67Fe4Mo2Si17B11 metallic glass ribbon has been subjected to the isotherma l annealing at temperatures in the range 250-600 degrees C so as to produce a series of samples with gradually coarser microstructure. For this series of samples a giant increase of the coercivity, exceeding five orders of ma gnitude, is observed. It shows a possibility to tailor soft or hard magnets using the same parent material. An abrupt increase of the coercivity occur s in a relatively small range of annealing temperatures between 480 and 520 degrees C, and is mainly due to a strengthening of the pinning effect of t he precipitates (fine crystalline structure) on the domain walls. Samples a nnealed at higher temperatures become fully crystallized. First, the metast able phase(s) is created which decomposes to the stable phases at still hig her temperature. Coercivity for fully crystallized samples shows first a na rrow plateau and afterwards a gradual decrease of its value with increasing temperature of annealing. Magnetic and microstructural properties of the s amples, annealed at various temperatures, were investigated applying a numb er of complementary techniques including DSC and TGM methods, X-ray diffrac tion, TEM, strain-modulated FMR spectroscopy as well as conventional magnet ic measurements. (C) 1998 Elsevier Science B.V. All rights reserved.