Doctoral Thesis
Current Induced Magnetization Dynamics in Nanostructures
Final Thesis 6.38 MB Summary of Thesis 792.04 kBAuthor of thesis: Ing. Vojtěch Uhlíř, Ph.D.
Acad. year: 2010/2011
Supervisor: prof. RNDr. Tomáš Šikola, CSc.
Reviewer: The opponent will be displayed after his opinion is published.
Abstract:This thesis deals with the study of current-induced magnetization dynamics and domain wall (DW) motion in NiFe/Cu/Co nanowires, induced by the so-called spin-transfer torque effect. Prior to this work, transport measurements had proven that in this trilayer system, DWs in NiFe can be moved with relatively low current densities, suggesting a particularly high spin-torque efficiency. The aim of this study has been to use photoemission electron microscopy combined with x-ray magnetic circular dichroism at synchrotron radiation sources to observe directly the magnetic configurations in the trilayers and their evolution during and after the application of nanosecond current pulses.
An important step of the work has been to optimize the growth of the NiFe/Cu/Co layers, in the view of increasing interface quality and minimize interlayer coupling. The process of nanowire patterning by e-beam lithography has also been optimized. Two kinds of measurements have been carried out: i) quasi static measurements, where the domain configuration is observed before and after the application of current pulses and ii) dynamic measurements, where the magnetic configuration has been observed during the application of current pulses. The first measurements have allowed us to study the statistical behaviour of DWs under the application of current pulses: on one hand, the domain wall velocities reach extremely high values for relatively low current densities (up to 600 m/s for 5x10^11 A/m^2). On the other hand, DW motion over distances larger than 2-3 microns is strongly hindered by pinning. Time-resolved measurements during the current pulses, carried out for the first time by our team, have allowed us to demonstrate that the NiFe magnetization is strongly tilted in the direction transverse to the nanowire direction, due to the presence of a transverse Oersted field. This effect might contribute to the enhancement of DW velocities in the NiFe layers.
spin-transfer torque, domain wall, magnetization dynamics,\magnetic nanowires, current-induced domain wall motion, spin-valve multilayers
Date of defence
29.10.2010
Result of the defence
Defended (thesis was successfully defended)
Process of defence
viz.zápis z obhajoby
Language of thesis
English
Faculty
Department
Study programme
Physical and Materials Engineering (3910V)
Field of study
Physical and Materials Engineering (D-FMI)
Composition of Committee
Alain Fontaine (předseda)
André Thiaville (člen)
Dafiné Ravelosona (člen)
Stefania Pizzini (člen)
Roman Antoš (člen)
prof. RNDr. Tomáš Šikola, CSc. (člen)
Supervisor’s report
prof. RNDr. Tomáš Šikola, CSc.