Abstract
We demonstrate high precision controllability of the magnetization reversal nucleation process in [Co/Pd]8 multilayer films consisting of two sets of bilayers with high and low perpendicular anisotropy, respectively. The anisotropy of the entire film is set by the degree of Co/Pd interfacial mixing during deposition which provides fine control of the anisotropy of an individual bilayer in the multilayer stack. The relative number of each type of bilayer is used to select the magnetisation reversal behavior such that changing one bilayer changes the properties of the entire multilayer through anisotropy averaging. A simple extension to the sputtering protocol would provide multilayer films with fully graded anisotropy, while maintaining a constant saturation magnetization opening new possibilities for the creation of highly engineered multilayer structures for spin torque devices and future magnetic recording media.
Highlights
The magnetisation reversal properties of perpendicular magnetic anisotropy materials (PMA), such as Co/Pd multilayer thin films,1,2 are important for future nanoscale technologies such as bit patterned media (BPM) recording3,4 and spin-torque transfer (STT) devices.5–7The reversal behavior of magnetic thin films with perpendicular anisotropy has been studied extensively8 and it is widely accepted that the reversal mechanism is one dominated by nucleation followed by rapid domain-wall motion.9 Reversal is nucleated at regions of low anisotropy which for materials of similar distributions of anisotropy means that the nucleation field is related to the average anisotropy in a consistent manner
We introduce the notation that bilayers with a high perpendicular anisotropy are referred to hard layers (HL), whilst those with a low perpendicular anisotropy are referred soft layers (SL)
Scherrer16 analysis was performed on the Co/Pd (111) peak to assess the estimated grain size measured via perpendicular scattering
Summary
The magnetisation reversal properties of perpendicular magnetic anisotropy materials (PMA), such as Co/Pd multilayer thin films, are important for future nanoscale technologies such as bit patterned media (BPM) recording and spin-torque transfer (STT) devices.. The reversal behavior of magnetic thin films with perpendicular anisotropy has been studied extensively and it is widely accepted that the reversal mechanism is one dominated by nucleation followed by rapid domain-wall motion.. The first is when the energy barrier associated with nucleation is greater than the barrier for domain-wall pinning. The second extreme occurs when the energy barrier due to the nucleation is less than that for domain-wall pinning such that following nucleation domain-walls may become trapped by pinning sites requiring additional applied reverse field to complete magnetisation reversal and achieve saturation.. This process allows us to tailor the anisotropy at the level of a single bilayer repeat whilst crucially maintaining the crystallographic structure, microstructure, and saturation magnetisation.
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