Reinvestigation of the intrinsic magnetic properties of (Fe1-xCox)2B alloys and crystallization behavior of ribbons

•The Callen-and-Callen model cannot explain the temperature dependence of the anisotropy constant.•A realistic electronic structure analysis with disordered moments approach is given.•It successfully accounts for the temperature and concentration dependence of the anisotropy.•Melt-spinning experiment indicates that this system shows rapid crystallization. New determination of the magnetic anisotropy from single crystals of (Fe1-xCox)2B alloys are presented. The anomalous temperature dependence of the anisotropy constant is discussed using the standard Callen-Callen theory, which is shown to be insufficient to explain the experimental results. A more material specific study using first-principles calculations with disordered moments approach gives a much more consistent interpretation of the experimental data. Since the intrinsic properties of the alloys with x=0.3-0.35 are promising for permanent magnets applications, initial investigation of the extrinsic properties are described, in particular the crystallization of melt spun ribbons with Cu, Al, and Ti additions. Previous attempts at developing a significant hysteresis have been unsuccessful in this system. Our melt-spinning experiment indicates that this system shows rapid crystallization.