Effects of NiFe/Co Insertion at the [Pd/Co] and Cu Interface on the Magnetic and GMR Properties in Perpendicularly Magnetized [Pd/Co]/Cu/[Co/Pd] Pseudo Spin-Valves

Perpendicularly magnetized [Pd/Co]₂/Cu/[Co/Pd]₄ pseudo spin-valves (PSVs) are promising in spintronic device applications. However, a large coercivity of the soft [Pd/Co]₂ ferromagnetic layer due to a high perpendicular anisotropy is revealed as a drawback for the device applications. In order to reduce the coercivity of the soft layer, a thin NiFe layer of 0-1 nm was inserted at the interface between the soft [Pd/Co]₂ layer and the Cu spacer. It was observed that the soft layer coercivity dropped dramatically from 250 to 40 Oe (85% reduction) by increasing the NiFe thickness. The main physical reason for this decrease is the reduction in perpendicular anisotropy caused by the in-plane anisotropy of the NiFe layer with a thickness larger than 0.4 nm. The interlayer coupling field was also increased mainly due to the increase in topological coupling induced by a rougher surface roughness attributed to Ni-Cu inter-diffusion. Due to this Ni-Cu intermixing, there is an increase in spin-independent scattering at the interfaces leading to an incidental decrease in the giant magnetoresistance (GMR). To improve the GMR performance in this structure, a thin Co layer of 0.1-0.6 nm was inserted at the interface between the NiFe layer and the Cu spacer while keeping the total NiFe/Co thickness constant at 0.5 and 0.7 nm, respectively. The Co insertion was found to be effective in protecting against the Ni-Cu intermixing leading to a 26% and 70% improvement in the GMR ratio up to 0.3 nm of Co insertion thickness with a further 65% and 75% reduction in the soft layer coercivity for a NiFe initial thickness of 0.5 and 0.7 nm, respectively. The experimentally confirmed results in this work demonstrate that NiFe/Co insertion at the interface between [Co/Pd] ferromagnetic layer and Cu spacer is effective in obtaining an optimum condition where the soft layer coercivity (anisotropy) is reduced while maintaining higher GMR ratio in the perpen- - dicularly magnetized [Pd/Co]/Cu/[Co/Pd] PSVs.