  The B2-ordered alloy FeRh shows a metamagnetic phase transition, transforming
from antiferromagnetic (AF) to ferromagnetic (FM) order at a temperature
$T_\mathrm{t} \sim 380 $~K in bulk. As well as temperature, the phase
transition can be triggered by many means such as strain, chemical doping, or
magnetic or electric fields. Its first-order nature means that phase
coexistence is possible. Here we show that a phase boundary in a 300~nm
diameter nanopillar, controlled by a doping gradient during film growth, is
moved by an electrical current in the direction of electron flow. We attribute
this to spin injection from one magnetically ordered phase region into the
other driving the phase transition in a region just next to the phase boundary.
The associated change in resistance of the nanopillar shows memristive
properties, suggesting potential applications as memory cells or artificial
synapses in neuromorphic computing schemes.
