Impact of He+ ion irradiation on the domain wall dynamics in Pd/Co/Pd trilayers with perpendicular magnetic anisotropy

Abstract

Heavy metal/ferromagnetic-based heterostructures with perpendicular magnetic anisotropy (PMA) are prototypes for domain wall (DW)-based spintronic devices. We explored the impact of He + ion irradiation on the bubble DW dynamics in Pd/Co/Pd trilayers with PMA. The effective magnetic anisotropy ( K e f f ) is enhanced by 20% when irradiated at the lowest fluence value, 1 × 1 0 14 He + / cm 2 and further, it decreases with an increase in fluence. Field-induced domain wall motion studies revealed that the sample irradiated at this fluence required a higher magnetic field for bubble domain walls to attain the same velocity as in the pristine sample. The bubble domain walls in the sample irradiated at this fluence expand at a rate of 1.1 mm/s, in contrast to the pristine sample’s rate of 0.38 mm/s near the coercive region, and this expansion rate diminishes with increasing fluence. At the lowest fluence value, bubble domains increase in size while their number density diminishes. However, with increased fluence, the size of the bubble domains reduces and their number density rises. Higher fluence values increase the interlayer roughness, driven by ballistic collisions between low-energy ions and atoms. The enhanced intermixing at higher fluence results in reduced saturation magnetization and anisotropy energy. Thus, by engineering the interfaces of the heterostructure and the magnetic anisotropy, ion interactions can be used to tune the pinning-controlled dynamics of magnetic bubble domains in Pd/Co/Pd based spintronic devices.