Chemical segregation mechanism and magnetic properties of Sm2Co17-based permanent magnets: experimental investigation and first-principles calculations

The magnetic properties and chemical segregation have led to an increased interest in Sm ₂Co ₁₇ -based magnets. This investigation employs experiments and first-principles calculations to obtain more profound comprehension of segregation and coercivity mechanism. The Sm(Co _balFe _0.25Cu _0.06Zr _0.02) _7.5 alloy exhibits a chemically heterogeneous cellular structure with Fe-rich 2:17R cells (60–70 nm) and Fe- and Cu-rich 1:5 cell boundaries (8–10 nm), and achieves excellent magnetic properties with a B _r of 11.69 kGs, an H _cj of 30.96 kOe and a ( BH) _max of 33.0 MGOe. First-principles calculations are performed on Sm ₆Co _51–xM _x and SmCo _5–yM _y (M = Fe, Cu) unit cells to identify their substitution energy ( E _s) and electronic structure. In Sm ₆Co _51–xM _x, Fe atoms preferentially occupy the 6c and 18f Co sites, whereas Cu replacement is unlikely to occur due to its positive E _s values. The segregation of Fe into the 2:17R structure is due to the decrease in the total density of states (DOS) at the Fermi level ( E _F) and the introduction of Fe-Co covalent-like bonding. By comparison, Fe and Cu atoms are both helpful for stabilizing the 1:5 phase, with Cu atoms first occupying the 2c site ( E _s = −1.697 eV/f.u.) and Fe atoms first occupying the 3g site ( E _s = −1.627 eV/f.u.). This small energy difference further explains the existence of Fe atoms in the 1:5 phase during ageing, which could significantly increase the magnetization. The segregation of Cu to the 1:5 phase is attributed to the formation of a pseudogap or bandgap at E _F . Ultimately, we furnish an extensive elucidation of the commonly acknowledged domain wall pinning coercivity mechanism at ambient temperature according to SmCo _5–yCu _y cell boundary phases.