Pressure-induced structural transition in intermetallic compounds MnRhP and MnRhAs

Pressure-induced structural transitions in MnRhP and MnRhAs were studied by in situ angle-dispersive X-ray diffraction using synchrotron radiation and a diamond anvil cell. A transition from a hexagonal Fe2P-type structure to an orthorhombic one was observed in MnRhP at a pressure of approximately 34 GPa. The first-nearest neighboring Mn–Mn interatomic distance at this transition pressure is close to the distance at which the sign of the effective exchange interaction coefficient between Mn atoms turns from positive to negative. A structural phase transition was also observed in MnRhAs at around 26 GPa, although the crystal system of the high-pressure phase was undetermined.