Magnetovolume Effect and Negative Thermal Expansion in Mn3(Cu1-xGex)N

Metallic manganese nitrides Mn3AN (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 ~ 100 K) and large negative thermal expansion (NTE) is exhibited around room temperature [(alpha)=-12 × 10^-6 K^-1 ((alpha): coefficient of linear thermal expansion) for Mn3(Cu0.5Ge0.5)N]. Such a large, isotropic and nonhysteretic NTE is desirable for practical applications.