Magnetic excitations in MnP

We performed inelastic neutron scattering experiments on a three-dimensional magnetic system MnP, which is a ferromagnetic inter-metallic compound below TC 291 K and transitions into a screw state at T ^* 47 K. Using newly developed high resolution chopper spectrometer (HRC) and triple axis spectrometer LTAS (for E 0-2 meV), 6G (for E 2-8 meV) TAS1 (for E 10-35 meV), we succeeded in observing the excitations from low energy to Brillouin zone center. We assumed isotropic 6 exchange parameters, and calculated dispersion relation using Heisenberg model for 2-sub lattices. We confirm that nearest neighbor (n.n) exchange parameters Jm are J > 0 (ferromagnetic interaction), the next nearest neighbor (n.n.n) exchange parameters are J < 0 (anti-ferromagnetic interaction), We conclude that the competition between n.n and n.n.n would be the cause of helimagnetic structure in MnP.