Investigating magnetisation dynamics in magnetic thin films and micro-structures

Abstract

Data storage is the fulcrum on which technology advances. As the rate of consumption of data increases there is growing demand from the storage industry for faster, more efficient storage solutions which is capable of storing more information per unit area. Non-volatile magnetic memory based on spin-electronics is one of the key proponents for addressing this demand. In order to develop such a memory it is necessary to attain a better understanding of the magnetic properties on which this is based.
This thesis aims to develop a tool to study the magnetisation dynamics of the free layer in a Pseudo Spin-Valve (PSV) of the form Co/Cu/NiFe utilising both the Giant Magneto-Resistance (GMR) and the Anisotropic Magneto-Resistance (AMR) effects. The key difference in the resistance responses of each of these effects is exploited here to showcase a proof of concept device which can be used as another method to aid in the study of magnetisation dynamics. GMR’s resistance response is dependent on the relative orientations of magnetisation between the free layer and the pinned layer. The AMR’s resistance response however, depends on the relative orientations of the magnetisation and the current direction. However, the resistance response of AMR is independent of magnetisation parallel or anti-parallel to current. This independence and the dependence of GMR on the relative magnetisations in each layer are used in combination to study the evolution of the magnetisation in a free layer PSV.
The magneto-resistance of the Co/Cu/NiFe spin-valve was measured in as deposited samples and samples deposited in the presence of an in-plane field. The magneto-resistance was compared to a PSV with an insertion of a Co layer at the Cu/NiFe interface. An L-shaped device was designed and patterned which could be used to study the magnetisation reversal in the NiFe free layer. This was done by tuning the RKKY coupling between the Co and NiFe, shape anisotropy of the patterned micro-wire and the Anisotropic Magneto-Resistance ratio of the NiFe in the pseudo-spin-valve.