Magnetic and electrical transport properties of artificial spin ice

Abstract

This thesis explores the mechanisms of the magnetic reversal of permalloy artificial spin ice arrays. The main research foci include the influence of domain wall propagation on the magnetic reversal of honeycomb artificial spin ice, the low temperature behaviour of honeycomb artificial spin ice and the classification of inverse permalloy opals as three dimensional artificial spin ice. Room temperature imaging of the magnetisation configuration of the nanobars through the magnetic reversal, via scanning transmission X-ray microscopy, photoemission electron microscopy and Lorentz transmission electron microscopy, showed non random domain wall propagation through the frustrated vertices of the honeycomb artificial spin ice arrays. OOMMF simulations suggest that the origin of such non-randomness lies in the domain wall chirality. Boundary conditions necessary for domain wall injection into artificial spin ice arrays were investigated. A reduction of the edge nanobars width of 2/3 was needed to prevent random domain wall nucleation from the array edges. Electrical transport measurements showed evidence of a change in the magnetic reversal, driven by domain wall propagation, of honeycomb permalloy artificial spin ice below 15 K. The transition temperature was found to be proportional to the square of the saturation magnetisation of the ferromagnetic material used. The change in the magnetic reversal was associated with the non-random vertex domain wall positioning below the transition temperature due to the influence of vertex dipole interactions. Room temperature Lorentz transmission electron microscopy images and temperature dependent electrical transport measurements of three dimensional permalloy inverse opals showed the potential of magnetic inverse opals to act as three dimensional artificial spin ice systems.