Berlin 2018 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 10: Skyrmions I (joint session MA/KFM/TT)
MA 10.2: Vortrag
Montag, 12. März 2018, 15:30–15:45, EB 301
Skyrmion bubble size and density control in Ta/CoFeB/MgO wedges — •Christian Denker1, Sören Nielsen2, Enno Lage2, Jeffrey McCord2, and Markus Münzenberg1 — 1Institut für Physik, Universität Greifswald, Germany — 2Nanoscale Magnetic Materials - Magnetic Domains, Institute for Materials Science, Universität Kiel, Germany
After the observation of skyrmion bubbles at room temperature in Ta/CoFeB/TaOx layers by A. Hoffmann’s group, skyrmions have been found in various heavy metal/ferromagnet/oxide systems. For skyrmion generation and detection by magnetic tunnel junctions (MTJ), the Ta/CoFeB/MgO system is appealing due to high TMR ratios and its technological maturity. As a starting point typical MTJ bottom electrodes and barriers (5 nm Ta/x CoFeB/3 nm MgO) trilayers with an optional Ru capping were deposited by e-beam evaporation (MgO, Ru) and magnetron sputtering (Ta, CoFeB). We will present our results on skyrmion bubbles observed by magneto-optical Kerr effect microscopy as function of continuous variation of CoFeB thickness. The in- to out-of-plane transition for the magnetic anisotropy is found at about x = 1.4 nm. At slightly thinner CoFeB thicknesses skyrmions can be nucleated. Their size can be as small as 300 nm. The influence of CoFeB composition and annealing temperature on the skyrmion formation, as well as skyrmion stability will be discussed.