  First order phase transitions occur discretely from one state to another,
however they often display continuous behavior. To understand this nature, it
is essential to probe how the emergent phase nucleates, interacts and evolves
with the initial phase across the transition at microscopic scales. Here, the
prototypical first-order magneto-structural transition in FeRh is used to
investigate these phenomena. We find that the temperature evolution of the
final phase exhibits critical behavior. Furthermore, a difference between the
structure and magnetic transition temperatures reveals a novel intermediate
phase created from the interface between the initial and nucleated final
states. This emergent phase, characterized by its lack of spin order due to the
competition between the antiferromagnetic and ferromagnetic interactions, leads
to suppression of the dynamic aspect of the transition, generating a static
mixed-phase-morphology. Understanding and controlling the transition process at
this spatial scale is critical to optimizing functional device capabilities.
