Studies of magnetic nanostructure for spintronics application

Date of Completion

January 2011

Keywords

Physics, Solid State|Physics, Electricity and Magnetism|Engineering, Materials Science

Degree

Ph.D.

Abstract

Spintronics is an emerging technology that exploits electron spin for information storage and processing. The work of this thesis contains studies of several key components of typical spintronics device, the magnetic tunneling junction (MTJ). It includes studies of: (i) high-spin polarization ferromagnetic electrodes, (ii) an interface between ferromagnetic and insulator tunneling barrier layer, and (iii) thin antiferromagnetic (AFM) films used for exchange biasing. The films of these materials were synthesized by molecule beam epitaxy (MBE) and pulse laser deposition (PLD) techniques and their electronic and spin structure were studied by photoemission spectroscopy (PES) combined with other conventional techniques. ^ (i) Studies of half-metallic ferromagnets (HMF), which should be the ideal materials for spintronics, have focused on Sr2FeMoO 6 (SFMO) thin films. From systematic studies of the effect of growth parameters we show that it is possible to grow high quality SFMO thin films. By fine-tuning the growth parameters we were also able to achieve surface electronic structure that is representative of SFMO bulk. Together, this work makes an important contribution to the fabrication of high quality HMF films and advanced MTJ junction, and it also opens the way to directly probe theoretical models describing this HMF material.^ (ii) The electronic and magnetic properties of technologically relevant interface between Fe and MgO layers have been studied in order to better understand maximum achievable tunneling magnetoresistance (TMR) in such MTJ structures. We show that MgO/Fe(100) interface can be grown without any presence of FeO interface layer, which was predicted to have negative effect on the magnitude of TMR. Furthermore, by measuring the spin-resolved band structure of Fe/MgO interface we show that magnetically sharp interface can be achieved and that they can be further sharpened by annealing.^ (iii) The magnetic properties of antiferromagnetic (AFM) NiO thin films grown on curved Ag(001) substrate were investigated using x-ray Magnetic Linear Dichroism (XMLD) technique. Atomic steps on a vicinal Ag(001) surface induce an in-plane uniaxial magnetic anisotropy, which provided an alternative method to control the spin direction of AFM layer in a hard-drive read head. ^

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