Co/Pd-Based synthetic antiferromagnetic thin films on Au/resist underlayers: towards biomedical applications

Abstract

Thin film stacks consisting of multiple repeats M of synthetic antiferromagnetic (SAF) [Co/Pd]_N/Ru/[Co/Pd]_N units with perpendicular magnetic anisotropy were explored as potential starting materials to fabricate free-standing micro/nanodisks, which represent a promising candidate system for theranostic applications. The films were directly grown on a sacrificial resist layer spin-coated on SiO_x/Si(100) substrates, required for the preparation of free-standing disks after its dissolution. Furthermore, the film stack was sandwiched between two Au layers to allow further bio-functionalization. For M ≤ 5, the samples fulfill all the key criteria mandatory for biomedical applications, i.e., zero remanence, zero field susceptibility at small fields and sharp switching to saturation, together with the ability to vary the total magnetic moment at saturation by changing the number of repetitions of the multi-stack. Moreover, the samples show strong perpendicular magnetic anisotropy, which is required for applications relying on the transduction of a mechanical force through the micro/nano-disks under a magnetic field, such as the mechanical cell disruption, which is nowadays considered a promising alternative to the more investigated magnetic hyperthermia approach for cancer treatment. In a further step, SAF microdisks were prepared from the continuous multi-stacks by combining electron beam lithography and Ar ion milling, revealing similar magnetic properties as compared to the continuous films.