${\rm HfCo}_{7}$ -Based Rare-Earth-Free Permanent-Magnet Alloys

This study presents the structural and magnetic properties of melt-spun HfCo₇,HfCo_7-xFe_x (0.25 ≤ × ≤ 1) and HfCo₇Si_x(0.2 ≤ × ≤1.2) alloys. Appreciable permanent-magnet properties with a magnetocrystalline anisotropy of about 9.6-16.5 Mergs/cm³, a magnetic polarization J_s ≈ 7.2-10.6 kG, and coercivities H_c = 0.5-3.0 kOe were obtained by varying the composition of these alloys. Structural analysis reveals that the positions of x-ray diffraction peaks of HfCo₇ show good agreement with those corresponding to an orthorhombic structure having lattice parameters of about α = 4.719 Å, b = 4.278 Å, and c = 8.070 Å. Based on these results, a model crystal structure for HfCo₇ is developed and used to estimate the magnetic properties of HfCo₇ using density-functional calculations, which agree with the experimental results.