Effect of impurities on magnetic properties of Y(Co5-xCux) and Y2(CO7-xNix)

Doping of the magnetic materials SMCo5 and Sm2Co7 with Cu or Ni enhances the magnetic properties by aligning otherwise independent domains. However, this doping with non-magnetic elements also decreases the magnetic moments of the Co atoms, which we have studied using density functional theory (DFT) calculations. Since localized Stin f-orbitals are very difficult to study within DFT calculations, we have studied Y(Co5-xCux), Y(Co5-xFex), and Y-2(Co7-xNix). While the total magnetic moments appear to follow the virtual crystal approximation (VCA) for the Ni and Cri doping, the localized moments on the Co atoms reduce much slower than expected from the VCA before suddenly dropping to zero at a critical concentration. The magnetic moments of Y(Co5-xCux) have been studied as a function of unit cell volume and c/a ratio which show sudden decreases in both the total and localized moments. In contrast, the magnetic moments of Y(Co5-xFex) increase with doping, but the magnetic anisotropy energy decreases, which is not useful technologically. (C) 2003 Elsevier B.V. All rights reserved.