Domain walls in hybrid ferromagnetic/piezoelectric structures
The energy needed to switch a <100 nm magnetic element in a memory device is currently a few pJ, and is mostly wasted by resistive heating. The magnetic energy required is only in the range of a few fJ, showing that fundamentally there is scope for an improvement in the switching efficiency by a factor 1000.
A novel solution enabling the development of low-power magnetic devices is emerging based on electric field effects on magnetic thin films with preferred magnetization direction out-of-plane, so-called perpendicular magnetic anisotropy, which are suitable for scaling to the smallest devices.
As a first step, we have used the strain coupling between a piezoelectric material, which changes shape in response to an electric field, to electrically control the anisotropy in Co/Pt, a model perpendicular magnetic thin film system, and to modify the field-driven switching in the film. The next task is to investigate the strain effect on current-driven switching.
The mechanism of switching is the motion of magnetic domain walls, and depends on the magnetic structure of the wall and the nature of the current-induced torques on magnetic moments in the wall.
This project will use highly magnetostrictive perpendicular thin films such as CoPd coupled to piezoelectrics, and investigate the electric field effect on anisotropy, domain wall structure and wall motion.
A spin-orbit coupling phenomenon known as the Dzyaloshinskii-Moriya interaction governs the domain wall structure and may also be influenced by electric field, allowing the transformation of domain walls into topologically protected spin structures such as skyrmions.
This opens up exciting new possibilities for research, as well as new device paradigms.
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FTE Category A staff submitted: 24.00
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