Spindynamik in Tunnelelementen mit senkrechter magnetischer Anisotropie
Spin dynamics in tunnel junctions with perpendicular magnetic anisotropy
Vladyslav Zbarsky
Doctoral thesis
Date of Examination:
2015-01-22
Date of issue:
2015-02-11
Advisor:
Münzenberg, Markus Prof. Dr.
Referee:
Münzenberg, Markus Prof. Dr.
Referee:
Jooß, Christian Prof. Dr.
Persistent Address: http://hdl.handle.net/11858/00-1735-0000-0022-5DB6-E
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Abstract
English
During the last thirty years the memory space per square centimeter on the memory unit was increased exponential. The reason for such strong improvement is the continuous decreasing of the unit cells down to nanometer scale, which in turn is the result of many years research of new materials and their applications. During this time a lot of new methods for memory cell fabrication, patterning and read/write processes were developed and optimized. On the field of energy efficiency there was also a huge progress, so for example the development of the modern spin-transfer torque elements (STT-elements) leads to decreasing by the factor ca. 1.5 (compared with static CMOS) of the energy needed to switch the memory cell from "0" to "1" (or vice versa) [3, 4]. The rewriting and reading speed of the memory cells measured on the STT-junctions is in the area of few nanoseconds (newest cells even < 1 ns), which makes STT-devices comparable with conventional memory cells [1, 3, 4]. All this advantages make the magnetic tunnel junctions (MTJs) very attractive for applications. So the investigation and optimization of the CoFeB/MgO-junctions is of current interest and is also the central issue of this work. Especially the interest is on the junctions with perpendicular magnetic anisotropy and their advantages over the MTJs with in-plane magnetic anisotropy. The first chapter of this work is concerned with the theoretical background of the following experimental work. The fabrication methods of the full layer stacks, their patterning methods and characterization setups are presented in the chapter "Experimentelle Methoden". The magnetic anisotropy behavior of the samples fabricated in our group will be measured and discussed in the chapter "Auswertung". First measurement of the Spin-Transfer-Torque and the comparison of the switching current behavior with the literature is also presented in the chapter "Auswertung". The discussion contains also results of the measurements on the ultra short time scales, where the possible minority electrons spin channeling was observed.
Keywords: magnetic tunnel junction; perpendicular magnetic anisotropy; spin dynimics of CoFeB/MgO; STT; Spin-Transfer Torque; MTJ; spin transport; demagnetization; minority spins; magnetic behavior of CoFeB
