Berlin 2018 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 6: Magnetic nanoparticles (joint session MA/CPP)

CPP 6.1: Vortrag

Montag, 12. März 2018, 09:30–09:45, H 0112

Temperature dependence of the magnetic anisotropy of Pt/Co/Pt nanodots — •Stefan Freercks, Eva-Sophie Wilhelm, Carsten Thönnißen, Philipp Staeck, and Hans Peter Oepen — Center for Hybrid Nanostructures, Universität Hamburg, Germay

We use the anomalous Hall-effect to investigate the magnetization reversal of single Pt/Co/Pt nanodots (diameter <35nm, Co thickness< 1.5nm) with perpendicular magnetization. The dots are fabricated by electron beam lithography and ion milling out of thin multilayers[1]. Our technique allows for measuring from room temperature, where the nanodots are usually superparamagnetic, down to low temperatures, where the magnetization is blocked. Measuring the switching times, we find that the attempt frequencies given by the Néel-Arrhenius law are some orders of magnitude higher than the expected GHz regime. Simple considerations show that a temperature dependent anisotropy can very well explain such deviations, which gave the motivation for our investigation. We determined the anisotropy of the initial film and of nanodots as a function of temperature. The anisotropy shows a non-linear temperature dependence in films and dots, which proves our point that temperature effects cannot be neglected in the Néel-Arrhenius law. Furthermore, the temperature dependence varies for different nanodots. The latter variation reveals that generalizations in ensemble measurements have to be handled with care. Funding by DFG via SFB 668 is gratefully acknowledged. [1] A. Neumann et al. Nano Letters. 13, p2199-2203, (2013)