Evolution mechanisms of magnetic domains in Cr/SmCo/Cr amorphous/nano-crystalline structured thin films

Cr/SmCo/Cr tri-layer thin films were prepared by oblique magnetron sputtering and annealed at various temperatures. An amorphous-nano-crystalline (SmCo-Sm₂Co₁₇) heterostructure emerged at 500 °C, in which stripe domains with a micrometer scale and an abnormal stripe pattern can be observed using in situ Lorentz transmission microscopy and magnetic force microscopy. The interconversion between the stripe-type domain and dot-type domain can be controlled by the external magnetic field. The stripe domain patterns are stable in varying external fields and can be retained at low field strength (<3000 Oe). Raising the annealing temperature to 600 °C leads to an increase in the in-plane coercivity (H_c) and transforms the domain pattern to a dot type. The magnetic coupling multi-phase field method was applied to investigate the domain walls. The simulation results demonstrated that a certain uniaxial magnetocrystalline anisotropy and the pinning effect of nano-crystalline grains could be responsible for the formation and properties of these stripe domains. This work systematically clarifies the physical origin and the dynamic properties of the magnetic domain in these amorphous/nano-crystalline SmCo films. The restorable domain pattern provides the amorphous/nano-crystalline SmCo film with potential applications in heterostructure magnetic devices.