Subject Area B1: Hall-Micro Magnetometry on Ferromagnetic Structures
Guido Meier, Ulrich Merkt
Ballistic Hall micro-magnetometers are magnetic-field sensors consisting of GaAs heterostructures
with high electron mobilities.
The size of the sensors can be well adjusted to the size of the objects to be analyzed.
This enables highly sensitive magnetization measurements of ferromagnets and superconductors.
Number of current- and field-induced depinning processes of a domain wall from the notch of a permalloy nanowire.
The inset depicts a typical result of Hall-micro magnetometry. The
scanning-electron micrograph shows the nanowire on the Hall sensor.
With Hall-micro magnetometry it has been possible to demonstrate the pinning of magnetic vortices
due to artificial defects and to visualize the agitation between different defects. It has been also possible
to study the gradual movement of a domain wall with the resolution of a lattice constant.
We also conduct experiments on ferromagnetic rings and dipolar coupled electrodes for ferromagnet-semiconductor
devices as well as with the simulation of domain structures.
In this subject area we plan to investigate the current- and field-induced depinning and motion
of domain walls in nanowires with a notch.
The depinning is influenced by many parameters such as the geometry
of the notch, the type of the domain wall, the strength of the magnetic field as well as
the duration, amplitude and rise time of the current pulses.
Furthermore we want to study the stray fields of vortices and antivortices by Hall-micro magnetometry and
magnetic-force microscopy. Vortex gyrations are of particular interest since they might be used for
new ultrafast memory devices.
A. K. Geim, S. V. Dubonos, J. G. S. Lok, I. V. Grigorieva, J. C. Maan, L. Theil Hansen, and P. E. Lindelof,
"Ballistic Hall micromagnetometry",
Appl. Phys. Lett. 71, 2379-2381 (1997).
K. S. Novoselov, A. K. Geim, S. V. Dubonos, E. W. Hill and I. V. Grigorieva,
"Subatomic movements of a domain wall in the Peierls potential",
Nature 426, 812 (2003).
P. Lendecke, R. Eiselt, G. Meier, and U. Merkt
"Temperature dependence of domain-wall depinning in constricted permalloy nanowires",
J. Appl. Phys. 103, 073909-1-073909-4 (2008).
Hall-micro magnetometry of current-induced domain-wall motion
Stray fields of vortices and antivortices for possible memory devices