Magnetic structure and local lattice distortion in giant negative thermal expansion material Mn₃Cu_1-xGe_xN

Magnetic and local structures in an antiperovskite system, Mn ₃Cu_1-xGe_xN, with a giant negative thermal expansion have been studied by neutron powder diffraction measurement. We discuss (1) an importance of an averaged cubic crystal structure and a ΓG^5g antiferromagnetic spin structure for the large magneto-volume effect (MVE) in this itinerant electron system, (2) an unique role of a local lattice distortion well described by the low temperature tetragonal structure of Mn₃GeN for the broadening of MVE.