Pressure effects on static and dynamic spin properties in CrAs*

CrAs is an antiferromagnetic metal, which shows a helical spin structure accompanied by an abrupt lattice expansion at $T\rm_{N}$$\sim$260 K in ambient pressure. With applying pressure, this material shows superconductivity with a maximum transition temperature of $\sim$2 K. Since Cr has the spin degree of freedom, elucidating the magnetic contribution to the superconductivity is crucial to understand the pairing mechanism. Our neutron diffraction studies have revealed that the static magnetic order as well as the structural anomaly is suppressed with applying external pressure. Chemical pressure effect was also studied by substituting As by P, which is found to be almost the same as the external pressure. We also plan to show the magnetic excitations in undoped and P-doped CrAs measured by inelastic neutron scattering experiments, which will give useful information on a coupling between the magnetism and the superconductivity.