If your exchange spring is made using bilayers, ideally you would make
two layers with different material properties. It is possible to do
that in nmag, as shown in the documentation:
http://nmag.soton.ac.uk/nmag/current/manual/html/example_two_materials/doc.html
But to create a spring, the soft layer needs to be pinned to the hard
layer via interlayer exchange. Unfortunately, it is not yet possible to
simulate interlayer exchange in nmag as of version 0.2.1.
If you don't mind using finite difference method (see
http://nmag.soton.ac.uk/nmag/0.2/manual/html/tutorial/doc.html for the
difference), then checkout OOMMF (
http://math.nist.gov/oommf/) or mumax3
(
https://github.com/mumax/3). which allows interlayer (or rather,
inter-region*) exchange.
*The above two are not limited to multilayers only; since the exchange
between different materials is specified as inter-region parameter, you
can also simulate composites (e.g. self-assembled nanocomposite or
particle-matrix)
Ahmad Syukri bin Abdollah
Materials & Manufacturing Division,
School of Engineering,
Osaka University