Dresden 2014 – scientific programme

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MA: Fachverband Magnetismus

MA 22: Magnetization Dynamics I

MA 22.1: Talk

Wednesday, April 2, 2014, 09:30–09:45, HSZ 401

Pump-probe-experiments on individual atomic-scale superparamagnets — •Jan Hermenau, Andreas Sonntag, Johannes Friedlein, Stefan Krause, and Roland Wiesendanger — Institute of Applied Physics, University of Hamburg, Germany

In our experiments we investigate the fast thermal magnetization reversal of uniaxial atomic-scale magnets [1] using an all electrical pump-probe-scheme [2] implemented in a spin-polarized scanning tunneling microscopy setup.

During the pump-pulse, a temporal population asymmetry of the two magnetization directions is induced due to spin-transfer torque generated by a high spin-polarized tunnel current pulse. After a given time a small current pulse is used to probe the state of the magnet. From the thermal decay of the induced population asymmetry the intrinsic switching rate can be determined. In contrast to pump-probe experiments of Loth et al. the switching between two degenerate ground states can be investigated in absence of a magnetic field.

In our experiments we determine the switching rates of individual magnets at different temperatures. For temperature intervals of 22 K switching rates ranging over eight orders of magnitude are observed on a single magnet. The experiments reveal a deviation of the high switching rates from the predictions of the Néel-Brown-law. This is discussed in terms of multi-droplet nucleation und domain wall propagation.

[1] S. Krause et al., Phys. Rev. Lett. 103, 127202 (2009)

[2] S. Loth et al., Nature Physics 6, 340 (2010)