Abstract
Using Ga+ focussed ion beam irradiation of Ta/Pt/CoFeB/Pt perpendicularly magnetized nanowires, the nucleation and injection fields of domain walls into the nanowires is controlled. The nucleation and injection fields can be varied as a function of dose, however, the range of injection fields is found to be limited by the creation of a step in anisotropy between the irradiated and unirradiated regions. This can be altered by defocussing the beam, which allows the injection fields to be further reduced. The ability to define an arbitrary dose profile allows domain walls to be injected at different fields either side of an asymmetrically irradiated area, which could form the initial stage of a logic device. The effect of the thickness of the magnetic layer and the thickness of a Ta underlayer on the dose required to remove the perpendicular anisotropy is also studied and is seen that for similar Ta underlayers the dose is determined by the thickness of the magnetic layer rather than its anisotropy. This finding is supported by some transport of ions in matter simulations.
Highlights
INTRODUCTIONMagnetic nanowires have been widely studied due to possible applications in data storage and logic.[1,2] A domain wall separating two magnetic domains in a nanowire has shown great promise as a memory or logic bit due to the ability to move them at high speeds and to manipulate the properties of the domain walls.[3,4,5] Recently, focus has turned to perpendicularly magnetized materials where the large out-of-plane anisotropies lead to very narrow domain walls, which are promising for technological applications.[6,7] It has been shown that these walls can have very high velocities when driven by both fields and in-plane currents.[8,9]
We show that by varying the dose the domain wall injection field changes systematically and that by designing asymmetric irradiation profiles, domain walls can be injected into two sides of the same wire at different fields
The properties of the nucleation and propagation of domain walls in perpendicularly magnetized nanowires has been studied as a function of Ga+ ion dose
Summary
Magnetic nanowires have been widely studied due to possible applications in data storage and logic.[1,2] A domain wall separating two magnetic domains in a nanowire has shown great promise as a memory or logic bit due to the ability to move them at high speeds and to manipulate the properties of the domain walls.[3,4,5] Recently, focus has turned to perpendicularly magnetized materials where the large out-of-plane anisotropies lead to very narrow domain walls, which are promising for technological applications.[6,7] It has been shown that these walls can have very high velocities when driven by both fields and in-plane currents.[8,9] One requirement of these designs is the controlled injection of domain walls into the nanowires. The effects of changing the thicknesses of the magnetic layers and the Ta underlayer are studied
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