  We present self-assembly routes of metamagnetic FeRh nanoisland arrays using
sputter deposition processing. Controlling the growth parameters and epitaxy
allows tuning the size and shape of the FeRh nanoislands. While the phase
transition between antiferromagnetic and ferromagnetic order is largely
suppressed in nanoislands formed on oxide substrates via thermodynamic
nucleation, we find that metamagnetism is largely preserved in nanomagnet
arrays formed through solid-state dewetting. This behavior is strongly
dependent on the resulting crystal faceting of the nanoislands, which is
characteristic of each assembly route. Comparing the calculated surface
energies for each magnetic phase of the nanoislands reveals that metamagnetism
can be suppressed or allowed by specific geometrical configurations of the
facets. Furthermore, we find that the spatial confinement leads to very
pronounced supercooling and the absence of phase separation in the nanoislands.
Finally, the supported nanomagnets are chemically etched away from the
substrates to inspect the phase transition properties of self-standing
nanoparticles. We demonstrate that solid-state dewetting is a feasible and
scalable way to obtain supported and free-standing FeRh nanomagnets with
preserved metamagnetism.
