Adjustable Cryogenic Near-Zero Thermal Expansion and Magnetic Properties in Antiperovskite Mn3Cu0.5Ge0.5N0.78C0.22

An attractive cryogenic near-zero thermal expansion (ZTE) behavior was achieved in the Mn3Cu0.5Ge0.5N0.78C0.22 compound, spanning a broad temperature window of 120 K (5 K to 125 K) with an average coefficient of thermal expansion (CTE) of α = 0.68 × 10−6 K−1. Furthermore, the effect of sintering temperature and holding time on thermal expansion and magnetic properties were investigated. Two distinct magnetic phase transitions are evident in the magnetization–temperature (M-T) curve of Mn3Cu0.5Ge0.5N0.78C0.22, which precede the near-ZTE behavior. These two antiferromagnetic (AFM)-like ordering transitions are hypothesized to play a pivotal role in governing the ZTE behavior, as they induce two episodes of negative thermal expansion (NTE). The realization of ZTE behavior is thus attributed to the counterbalance of these two NTE contributions, which can be effectively tuned by varying the carbon content or optimizing the sintering process parameters. Collectively, these results demonstrate significant potential for the design of diverse cryogenic functional materials.