Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 50: [MA] Joint Session "Surface Magnetism I" (jointly with O)

O 50.1: Talk

Wednesday, March 28, 2012, 16:00–16:15, BH 243

Observation and quantitative evaluation of superparamagnetic behavior utilizing magnetic exchange force microscopy and spectroscopy — •Schwarz Alexander, Schmidt Rene, and Wiesendanger Roland — Institute of Applied Physics, University of Hamburg, Jungiusstr. 11, 20355 Hamburg, Germany

Magnetic exchange force microscopy (MExFM) and spectroscopy (MExFS) can resolve magnetic surfaces and probe the distance dependence of the magnetic exchange interaction with atomic resolution [1,2]. Here we show that the distance dependence of the magnetic exchange interaction can be utilized to modify the barrier height between two magnetization directions in a well-controlled manner. Contrast reversals observed with magnetically coated tips during imaging an antiferromagnetic surface show that tips can switch their magnetization direction by 180°. Since the magnetic exchange interaction is distance dependent, switching rate, lifetimes and the barrier height between the two states are distance dependent as well. Modeling the tip apex as superparamagnetic cluster with uniaxial anisotropy but otherwise independent of the rest of the tip, allows quantifying the energy barrier between both states as well as the zero field anisotropy. Moreover, the influence of a magnetic field via the additional Zeeman energy can be measured. Our study demonstrates the feasibility to observe dynamic magnetic processes utilizing magnetic exchange force microscopy and spectroscopy with atomic resolution.

[1] U. Kaiser et al., Nature 446, 522 (2007).

[2] R. Schmidt et al., Phys. Rev. Lett. 106, 257202 (2011).