Magnetovolume Effect and Negative Thermal Expansion in Mn₃(Cu_1−xGe_x)N

Abstract

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 (ΔT∼100 K) and large negative thermal expansion (NTE) is exhibited around room temperature [α=−12×10⁻⁶ K⁻¹ (α: coefficient of linear thermal expansion) for Mn₃(Cu_0.5Ge_0.5)N]. Such a large, isotropic and non-hysteretic NTE is desirable for practical applications.