Abstract
The role of B on the microstructure and magnetism of Zr16Co82.5-x Mo1.5B x ribbons prepared by arc melting and melt spinning is investigated. Microstructure analysis show that the ribbons consist of a hard-magnetic rhombohedral Zr2Co11 phase and a minor amount of soft-magnetic Co. We show that the addition of B increases the amount of hard-magnetic phase, reduces the amount of soft-magnetic Co and coarsens the grain size from about 35 nm to 110 nm. There is a monotonic increase in the volume of the rhombohedral Zr2Co11 unit cell with increasing B concentration. This is consistent with a previous theoretical prediction that B may occupy a special type of large interstitial sites, called interruption sites. The optimum magnetic properties, obtained for x = 1, are a saturation magnetization of 7.8 kG, a coercivity of 5.4 kOe, and a maximum energy product of 4.1 MGOe.
Highlights
We show that the addition of B increases the amount of hard-magnetic phase, reduces the amount of soft-magnetic Co and coarsens the grain size from about 35 nm to 110 nm
The powder X-ray diffraction (XRD) patterns were collected using a PANalytical Empyrean X-ray diffractometer with Cu Kα radiation, and the nanostructure was investigated by a FEI Tecnai Osiris Transmission Electron Microscope (TEM)
The full-width at half-maximum (FWHM) of diffraction peaks from Co at 45.06o increase with increasing x, which suggests that the mean grain size of Co decreases
Summary
Zr2Co11-based materials show promising intrinsic magnetic properties, including relatively high magnetocrystalline anisotropy, high Curie temperature, and hard magnetic properties, they have potential as cost-effective permanent magnets free of critical rare earths or expensive metals.[1,2,3,4,5] Alloys with the approximate stoichiometry Zr2Co11 crystallize in cubic, orthorhombic, and rhombohedral structures, but only the rhombohedral phase, which is predicted to be metastable by formation-energy calculations, leads to significant coercivity.[3,5,6] The structures are basically dense-packed, with structural motifs reminiscent of that in SmCo5.6 Rhombohedral Zr2Co11 is a high-temperature phase, whereas the orthorhombic phase is more stable at low temperatures. First-principle calculations[15] are consistent with both B substituting for Co and B occupying “interruption sites” between the motifs
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