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

Metallic manganese nitrides Mn 3 AN (A ¼ 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 Mn 3 CuN.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 (ÁT $ 100 K) and large negative thermal expansion (NTE) is exhibited around room temperature [ ¼ À12 Â 10 À6 K À1 (: coefficient of linear thermal expansion) for Mn 3 (Cu 0:5 Ge 0:5 )N].Such a large, isotropic and non-hysteretic NTE is desirable for practical applications.