Thermal annealing on the soft magnetism, microwave properties, and magnetostriction in Co-Fe-C alloy films

Abstract

Recently, Co-Fe-C alloy films have attracted much attention because of their excellent comprehensive magnetic properties such as better saturated magnetostriction constant (λs), magnetic softness, ferromagnetic resonance linewidth, and in-plane Gilbert damping, compared to the well-known Co-Fe-B alloy films. It is always acknowledged that thermal annealing can largely improve the properties of alloy films but no systematic study has been published on the Co-Fe-C alloy films so far. Moreover, it is reported that the Co-Fe-C alloy films with medium carbon doping possess high thermal stability, but there still be lack of mechanism explanation. Here, we report on the structure evolution, compositional uniformity, soft magnetism, microwave properties, and magnetostriction constant versus thermal annealing temperature (Tan) in the Co-Fe-C alloy films with three typical carbon contents. It can be concluded that thermal annealing will increase the grain sizes and drive the carbon elements moving towards the interface. The low and medium doping films maintain the crystallization and coexistence phase during thermal annealing respectively, which is different from the phase transition happening in the high doping films. The macroscopic magnetic anisotropy Mr/Ms, intrinsic magnetic anisotropy Ku, inhomogeneous line width broadening at 0 Hz ΔH0, and λs are all related to the strain releasing and assembling during thermal annealing. It indicates that the high thermal stability of the medium doping Co-Fe-C alloy films originate from the stable structure phase and elements distribution during thermal annealing. This work is helpful for fundamental understanding the impact of thermal annealing on the magnetic properties of amorphous and nanocrystalline alloy film, and it will guide the annealing technical development on the magnetic devices’ fabrication and capsulation.