Preparation, Characterization, and Modeling of Ultrahigh Coercivity Sm–Co Thin Films

Isotropic Sm–Co thin films with different Sm_xCo_y phases (1:7, 1:5, and 2:7) are prepared by triode sputtering of targets of variable composition. A room-temperature coercivity value of 6.8 T is achieved in the film with the SmCo₅ phase. Transmission electron microscopy (TEM) and 3D atom probe analyses of films that comprise this compound reveal the presence of Sm-rich 4-nm-sized precipitates within grains and along grain boundaries. Atomic-resolution scanning transmission electron microscopy/high-resolution high-angle annular dark-field (STEM/HAADF) imaging show that stacking faults occur within SmCo₅ grains, which correspond to local phase variants including Sm₂Co₇, Sm₅Co₁₉ and SmCo₃. The contribution to domain wall pinning of precipitates and stacking faults, as well as grain boundaries between misaligned grains, is discussed semi-quantitatively. Micromagnetic simulations are carried out to evaluate the influence of stacking faults and grain boundaries on magnetization reversal. The results indicate that the high coercivity values achieved can mainly be attributed to the strong pinning of magnetic domains at the grain boundaries of randomly oriented SmCo₅ nanograins.