Effects of nitrogen deficiency on the magnetostructural properties of antiperovskite manganese nitrides

Giant negative thermal expansion in antiperovskite manganese nitrides Mn(3)AN (A = Zn, Ga, etc.) is achieved by substituting Ge for A as a relaxant to the sharp volume change associated with the magnetic transition. We have studied the effects of nitrogen deficiency on the broadening of volume change. Although the broadening increases with decreasing nitrogen content for Mn3Cu0.5Ge0.5N1-delta, the sharp volume change is robust against nitrogen deficiency in Ge-free Mn3GaN1-delta. Nitrogen deficiency probably does not broaden the volume change by itself; rather it probably assists the broadening in conjunction with the Ge dopant. The origin of the broadening is discussed in terms of local lattice distortion of the Mn6N octahedra. (C) 2012 American Institute of Physics. [doi:10.1063/1.3672243]