Abstract
Magnetic patterning, with designed spatial profile of the desired magnetic properties, has been a rising challenge for developing magnetic devices at nanoscale. Most existing methods rely on locally modifying magnetic anisotropy energy or saturation magnetization, and thus post stringent constraints on the adaptability in diverse applications. We propose an alternative route for magnetic patterning: by manipulating the local intergranular exchange coupling to tune lateral magnetic properties. As demonstration, the grain boundary structure of Co/Pt multilayers is engineered by thermal treatment, where the stress state of the multilayers and thus the intergranular exchange coupling can be modified. With Ag passivation layers on top of the Co/Pt multilayers, we can hinder the stress relaxation and grain boundary modification. Combining the pre-patterned Ag passivation layer with thermal treatment, we can design spatial variations of the magnetic properties by tuning the intergranular exchange coupling, which diversifies the magnetic patterning process and extends its feasibility for varieties of new devices.
Highlights
Anisotropy and/or saturation magnetization, is it possible to find another tuning knob to realize magnetic patterning for device designs?
With pre-patterned passivation layers and thermal treatments, we demonstrate the magnetic patterning on Co/Pt multilayers (MLs), which are used as the model system due to its easy fabrication and perpendicular anisotropy for potential applications[23]
With rapid thermal annealing (RTA) process, we found that stress relaxation in Co/Pt MLs brings about modification of grain boundary structures and the corresponding magnetic properties
Summary
Anisotropy and/or saturation magnetization, is it possible to find another tuning knob to realize magnetic patterning for device designs?. One can engineer grain boundaries in recording media and permanent magnets for magnetic hardening, which may accompany modified intergranular exchange coupling. These approaches usually alter grain boundary structure uniformly in the entire sample and no spatial manipulation can be achieved. By adopting pre-patterned passivation layers, we can spatially control the degree of stress relaxation in the designated regions with lateral modulation of the nucleation field (Hn), the domain wall propagating field (Hp), and the domain structures in Co/Pt MLs. In addition, we find that the same magnetic patterning can be achieved by Joule heating. Our proposed approach opens up a new avenue for magnetic patterning and can be incorporated into the existing process for device fabrication, for example, the BEOL (back-end-of-line) process, how the magnetic devices are usually integrated with other components[24,25]
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