  Hexagonally structured MnRuP was studied under high pressure up to 35 GPa
from 5 to 300 K using synchrotron X-ray diffraction. We observed that a partial
phase transition from hexagonal to orthorhombic symmetry started at 11 GPa. The
new and denser orthorhombic phase coexisted with its parent phase for an
unusually long pressure range, {\Delta}P ~ 50 GPa. We attribute this structural
transformation to a magnetic origin, where a decisive criterion for the
boundary of the mixed phase lays in the different distances between the Mn-Mn
atoms. In addition, our theoretical study shows that the orthorhombic phase of
MnRuP remains steady even at very high pressures up to ~ 250 GPa, when it
should transform to a new tetragonal phase.
