Magnetovolume Effect and Negative Thermal Expansion in Mn_3(Cu_(1-x)Ge_x)N

摘要

Metallic manganese nitrides Mn_3AN (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 Mn_3CuN. 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 appox 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(Cu_(0.5)Ge_(0.5))N]. Such a large, isotropic and non-hysteretic NTE is desirable for practical applications.