The origin of coercivity enhancement in the Co77Zr18Cr3B2 magnet

• Cr substitution improved the coercivity significantly.
• High coercivity of 7.0 kOe was obtained in Co77Zr18Cr3B2.
• An enhancement in magnetocrystalline anisotropy field was observed in Co77Zr18Cr3B2.

The effects of a partial substitution of Cr for Co on the magnetic properties of Co80Zr18B2 alloy are investigated in this paper. An appropriate addition of Cr can improve the coercivity (iHc) significantly. The maximum iHc of 7.0 kOe is obtained in the melt-spun Co77Zr18Cr3B2 after annealed at 550 °C. X-ray diffraction (XRD) and thermomagnetic analysis (TMA) are employed to determine the phase composition. It is found that the sample is comprised of the single Co11Zr2 which is responsible for the magnetic hardness. The Cr atoms enter into the lattice of Co11Zr2 and increase the magnetocrystalline anisotropy field (Ha). SEM investigations show a microstructure consisting of equiaxed grains whose average size is about 300–350 nm. The origin of coercivity enhancement in Co77Zr18Cr3B2 is ascribed to the increase in Ha.