Controlling magnetic domain wall motion in the creep regime in He~+-irradiated CoFeB/MgO films with perpendicular anisotropy

摘要

This study presents the effective tuning of perpendicular magnetic anisotropy in CoFeB/MgO thin films by He~+ ion irradiation and its effect on domain wall motion in a low field regime. Magnetic anisotropy and saturation magnetisation are found to decrease as a function of the irradiation dose which can be related to the observed irradiation-induced changes in stoichiometry at the CoFeB/ MgO interface. These changes in the magnetic intrinsic properties of the film are reflected in the domain wall dynamics at low magnetic fields (H) where irradiation is found to induce a significant decrease in domain wall velocity (v). For all irradiation doses, domain wall velocities at low fields are well described by a creep law, where Ln(v) vs. H~(-1/4) behaves linearly, up to a maximum field H~*, which has been considered as an approximation to the value of the depinning field H_(dep). In turn, H~*≈H_(dep) is seen to increase as a function of the irradiation dose, indicating an irradiation-induced extension of the creep regime of domain wall motion.