and Micromagnetic Simulations
Barthelmeß, Guido Meier
In semiconductor spintronic devices that incorporate ferromagnetic
materials as electrodes, the magnetization must be well known in order to
control the electron spin. The magnetization of ferromagnetic micro- and
nano-structures depends on the material, the external magnetic field, the
geometry, and the interaction with adjacent ferromagnets .
With the computer code
OOMMF supplied by M. Donahue and D. Porter  we simulate ferromagnetic
microstructures in external magnetic fields and calculate the corresponding
magnetization pattern for each applied field. As an example, Fig. 1 shows the
domain structure in an iron electrode without external magnetic field in the
as-prepared state. It consists of two vortices separated by a so called
cross-tie wall . From the integral magnetization we obtain hysteresis curves
which can be compared to experimental results obtained from Hall-micromagnetometers
Fig. 1: Magnetization pattern of an iron microstructure (1µm x 2µm x 20nm).
From the magnetization we
can calculate the stray-field pattern and its second derivative which
corresponds to the signal of magnetic-force microscopy (MFM) data in arbitrary
distances to the ferromagnet. This allows direct comparison with the measured
images (see Fig. 2) .
Fig. 2: (a) Measured and (b) simulated MFM image of an iron
microstructure (1µm x 2µm x 20nm).
The simulated image is calculated from the magnetization pattern in Fig. 1.
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D.Porter, Oommf, object oriented micromagnetic framework, http://math.nist.gov/oommf
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