Structural and magnetic phase transitions in NdCoAsO under high pressures

We have investigated structural and magnetic phase transitions under high pressures in a quaternary rare-earth transition-metal arsenide oxide NdCoAsO compound that is isostructural to the high temperature superconductor parent phase NdFeAsO. The four-probe electrical resistance measurements carried out in a designer diamond anvil cell show that the ferromagnetic Curie temperature and antiferromagnetic Néel temperature increase with an increase in pressure. High pressure x-ray diffraction studies using a synchrotron source show a structural phase transition from a tetragonal phase to a new crystallographic phase at a pressure of 23GPa at 300K. The NdCoAsO sample remained antiferromagnetic and non-superconducting down to 10K and up to the highest pressure achieved in this experiment, 53GPa. A P-T phase diagram for NdCoAsO is presented from ambient conditions to P = 53GPa and T = 10K.