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The field dependence of the reversal mode is explained as follows: at low external fields
the reversal mode is mainly determined by the competition of exchange and strayfield energy.
At higher fields the Zeeman energy gets a stronger weight and it can get of advantage to
follow a more inhomogeneous mode. More energy is spent in exchange, but therefore
more energy is gained in the Zeeman part. In total the energy barrier is smaller even though the
mode has become more complex. This observation is shown in the plots on the right.
The four energy contributions along the minimum energy paths are compared for 62.5 nm particle size.
We compare the minimum energy path obtained with zero external field with the minimum energy
path obtained for Hext = 500 Oe. The exchange energy is 4 times higher at 500 Oe than at zero
field since the reversal mode involves the motion of a domain wall. The anisotropy energy
only plays a minor role which means that the shape of the particle and the external field
dominates the behavior of the reversal mode and height of the energy barrier.
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