Preparing and exploiting phase-change materials in the
nanoscale
form is an ongoing challenge for advanced material research. A common
lasting obstacle is preserving the desired functionality present in
the bulk form. Here, we present self-assembly routes of metamagnetic
FeRh nanoislands with tunable sizes and shapes. While the phase transition
between antiferromagnetic and ferromagnetic orders is largely suppressed
in nanoislands formed on oxide substrates via thermodynamic nucleation,
we find that nanomagnet arrays formed through solid-state dewetting
keep their metamagnetic character. 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 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.