  Phase coexistence across disorder-broadened and magnetic-field-induced first
order antiferromagnetic to ferrimagnetic transition in polycrystalline
$Mn_{1.85}Co_{0.15}Sb$ has been studied mesoscopically by Scanning Hall Probe
Microscope at 120K and up to 5 Tesla magnetic fields. We have observed
hysteresis with varying magnetic field and the evolution of coexisting
antiferromagnetic and ferrimagnetic state on mesoscopic length scale. These
studies show that the magnetic state of the system at low field depends on the
path followed to reach 120 K. The low field magnetic states are mesoscopically
different for virgin and second field increasing cycle when 120 K is reached by
warming from 5K, but are the same within measurement accuracy when the
measuring temperature of 120K is reached from 300K by cooling.
