Spin dependent transport in continuous and discontinuous CoFeB/MgO heterostructures

This thesis is devoted to the study of spin dependent transport between CoFeB electrodes through an MgO barrier in ordered and disordered multilayer systems. The local electrical integrity of the MgO barrier was studied using Ru and CoFeB bottom electrodes by a modified conducting atomic force microscopy. The quality of the MgO barrier was characterized by measuring the hotspot density and using a statistical model proposed by F. Bardou for different thicknesses of MgO. This model studied the variations in tunneling transmission due to inhomogeneity of the barrier. The results show a decrease of the density of the hotspots with the thickness of MgO barrier and that a perfectly insulating barrier is obtained at 1 nm thickness. For the study of the disordered systems, discontinuous multilayers of CoFeB/MgO were prepared by sequential sputtering of CoFeB and MgO from the individual targets. The granular tunneling magnetoresistance (g-TMR) and transport properties were studied between 1.25 K and 330 K. The transport of charge between CoFeB in this system was dominated by hopping processes which obeyed different tunneling laws in different temperature regions. The enhanced g-TMR value observed at low temperature was attributed to higher order tunneling. The study also focused on the variations in g-TMR, electrical resistivity and microstructures by post deposition annealing. The magnetic properties of this system were also investigated between 5 K and 350 K. A superparamagnetic transition was found with a blocking temperature of 130 K.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bielefeld

Year

2009

Author dc:creator

• Bhutta, Khalid Mehmood

Repository record source_url

https://pub.uni-bielefeld.de/record/2302305

OAI identifier oai:identifier

oai:pub.uni-bielefeld.de:2302305