Tunneling Spin Polarization and Magnetic Properties of Co–Fe–B Alloys and Their Dependence on Boron Content

Tunneling spin polarization (TSP) of (Co50Fe50)100-xBx alloys with various boron contents is measured by superconducting tunneling spectroscopy (STS). Because magnetic tunnel junctions (MTJs) using Co–Fe–B alloys exhibit a large tunnel magnetoresistance (TMR) effect, they are highly valued materials; in addition, the TSP of Co–Fe–B alloys is expected to be high. The maximum observed TSP value is 49% for (Co50Fe50)80B20, which is higher than that of pure Co50Fe50 (37%). An X-ray diffraction pattern showed that the structure of (Co50Fe50)80B20 is amorphous. We infer that the structure is changed to the amorphous state by increasing the boron content, which enhances the TSP of Co–Fe–B alloys.