Magnetization studies of binary and ternary Co-rich phases of the Co–Si–B system

CoB, Co2B, CoSi, Co2Si and Co5Si2B phases can be formed during heat-treatment of amorphous Co–Si–B soft magnetic materials. Thus, it is important to determine their magnetic behavior as a function of applied field and temperature. In this study, polycrystalline single-phase samples of the above phases were produced via arc melting and heat-treatment under argon. The single-phase nature of the samples was confirmed via X-ray diffraction experiments. AC and DC magnetization measurements showed that Co2Si and Co5Si2B phases are paramagnetic. Minor amounts of either Co2Si or CoSi2 in the CoSi-phase sample suggested a paramagnetic behavior of the CoSi-phase, however, it should be diamagnetic as shown in the literature. The diamagnetic behavior of the CoB phase was also confirmed. The paramagnetic behavior of Co5Si2B is for the first time reported. The magnetization results of the phase Co2B have a ferromagnetic signature already verified on previous NMR studies. A detailed set of magnetization measurements of this phase showed a change of the easy magnetization axis starting at 70 K, with a temperature interval of about 13 K at a very small field of 1 mT. As the strength of the field is increased the temperature interval is enlarged. The strength of field at which the magnetization saturates increases almost linearly as the temperature is increased above 70 K. The room temperature total magnetostriction of the Co2B phase was determined to be 8 ppm at a field of 1 T.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights▶ Co5Si2B phase was found to be paramagnetic, while Fe5SiB2 and Mn5SiB2 are ferromagnetic. ▶ Ferromagnetic Co2B phase showed magnetization curves evidence of the easy axis change at ∼ 70 K. ▶ The easy axis change in Co2B does not happen exactly at 70 K, but depends on the applied field; DT grows with the applied field increasing.