Suppression of Sm Segregation and Improvement in Thermal Stability by Introducing Ru Underlayer in Co–Sm Amorphous Films

Ru underlayer effects on the thermal stability of the magnetic properties in Co-Sm amorphous films have been investigated in terms of its robustness for the thermal-process in the fabrication of GHz band micro-magnetic devices. The anisotropy magnetic field H_k of the Co-Sm film was tending to decrease with an increase in the annealing temperature, but the reduction in H_k due to thermal-process became small by introducing the Ru underlayer. The high-resolution transmission electron microscopy (HR-TEM) observations revealed the presence of nanosized crystalline Sm segregation at the interface between the Co-Sm film and SiO₂/Si substrate in the films without Ru underlayer, while there is no Sm segregation in the film with Ru underlayer. Sm segregation and the subsequent thermally induced phase-separation are one of the factors for the reduction in H_k. Ru underlayer effectively prevents the segregation of crystalline Sm and the resulting reduction in H_k. High-frequency magnetic property of Co-Sm film with Ru underlayer was superior to that without Ru underlayer for same annealing condition.