Dresden 2006 – scientific programme
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MA: Magnetismus
MA 27: Spin-Dynamics, Magnetization Reversal II
MA 27.10: Talk
Thursday, March 30, 2006, 12:30–12:45, HSZ 403
Thermal Switching Behaviour of Superparamagnetic Nanoislands: SP-STM on Fe/W(110) — •Stefan Krause, Luis Berbil-Bautista, Matthias Bode, and Roland Wiesendanger — Institute of Applied Physics, University of Hamburg, Jungiusstraße 11, 20335 Hamburg
Spin-polarized scanning tunneling microscopy (SP-STM) is a well-established tool to reveal the static magnetic structure of surfaces at spatial resolution down to the atomic scale. Recently it has been shown that SP-STM can also be applied to investigate the dynamic switching processes in real time and real space, e.g. the thermal switching behaviour of individual superparamagnetic nanoislands [1]. While the experiments of Ref. [1] were performed only for a very limited temperature range, we have now used a home-built variable-temperature STM for detailed temperature-dependent investigations. This allows a critical examination of the predictions on the temperature-dependence of the switching rate made by the so-called Néel-Brown law. This theory predicts an Arrhenius-like behaviour for nanoparticles which are coherently magnetized even during the switching process.
Our sample consists of in-plane magnetized uniaxial Fe monolayer islands on W(110). For islands with an area of about 20 nm2 we find a blocking temperature of about 45 K. The high stability of our experimental setup allows the observation of the same islands over a wide temperature range. The experimental data will be discussed in terms of the particle’s anisotropy barrier and the attempt frequency.
[1] M. Bode et al., Phys. Rev. Lett. 92, 067201 (2004).