Structural characterisation of L10 ordered materials for spintronics

Abstract

L10 ordered materials offer considerable promise for enhancing the performance of current and future spintronic technologies, particularly magnetic data storage. The need for greater areal density fuels research into high anisotropy materials, such as L10 ordered FePt. MnAl is another L10 ordered material which has great potential as an efficient spin polariser for the development of magnetic tunnel junctions due to its low spin-orbit coupling. The magnetic properties of these materials depend on their crystal structure and degree of ordering. The work presented here concerns the structural characterisation of L10 ordered materials and the development of L10 ordered MnAl thin films. The additional parameter space offered by remote plasma sputtering was explored with a view to controlling the grain size of FePt thin films by varying the target bias voltage. A semi-automatic grain identification method was identified, improving the repeatability and reliability of the results. The average grain size and grain size distribution was found to increase after annealing, but was robust against variation in the target bias voltage. The structural properties of FeRh were investigated as a complementary material for next generation magnetic data storage applications. Island type growth was seen with considerable dewetting from the substrate. The degradation of the magnetic properties of these films with decreasing thickness was attributed to the decrease in crystal order as observed in this work. MnAl thin films were fabricated by co-sputtering. The formation of the metastable L10 phase was found to be highly sensitive to the elemental composition and processing temperatures used. Local ordering was observed which improved after annealing to give a maximum saturation magnetisation of 67 emu/cm3 . This work provides a strong grounding in the challenges associated with producing ferromagnetic, L10 ordered thin films of MnAl, and identifies directions for further research.

Date of Award	1 Aug 2018
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Thomas Thomson (Supervisor), Ernest Hill (Supervisor) & Sarah Haigh (Supervisor)