Magnetovolume effect and negative thermal expansion in Mn3(Cu1-xGex)N

Metallic manganese nitrides Mn(3)AN (A = Zn, Ga, etc) are well-known for their large magnetovolume effect (MVE), i.e., a discontinuous volume expansion at the magnetic transition. However, MVE is exceptionally absent in Mn3CuN. We found that MVE is recovered by a small amount of Ge in the Cu site. This revival seems to coincide with recovery of the cubic structure. By further Ge doping, the volume expansion becomes gradual (Delta T similar to 100 K) and large negative thermal expansion (NTE) is exhibited around room temperature [alpha = -12 x 10(-6) K-1 (alpha: coefficient of linear thermal expansion) for Mn-3(Cu0.5Ge0.5)N]. Such a large, isotropic and non-hysteretic NTE is desirable for practical applications.