Structure and Magnetic Properties of (001) Oriented CoPt-Ag and CoPd-Ag Alloy Films

Abstract

20-nm-thick (CoPt)100-xAgx and (CoPd)100-xAgx (001) films (x = 0-20) were grown on MgO(001) substrate at a temperature of 300ûC by molecular beam epitaxy, and their crystal structure and magnetic properties were compared with those of FePt-Ag and FePd-Ag films [Y. Tokuoka et al.: J. Appl. Phys., 115, 17B716 (2014)] for the systematic study of the effect of Ag addition into transition metal-noble metal alloy films. For the CoPt-Ag, the addition of 5% Ag increased perpendicular magnetic anisotropy (PMA) and coercivity. However, for the CoPd-Ag, Ag addition enhanced neither the PMA nor the coercivity. Structural analysis of the CoPt-Ag and CoPd-Ag films revealed that Ag addition promoted L10 phase ordering for CoPt-Ag, while L10 ordering was not found in CoPd-Ag. Although there were some similarities in the effect of Ag addition between CoPt-Ag and FePt-Ag, such as increased PMA, coercivity, and L10 ordering, there were different trends in PMA and L10 ordering between CoPd-Ag and FePd-Ag, except that both films showed reduced coercivity with Ag addition. Ag segregation and L10 ordering are considered important factors to explain the variations of structure and magnetic properties with Ag addition.