Tunable negative thermal expansion related with the gradual evolution of antiferromagnetic ordering in antiperovskite manganese nitrides Ag_1−xNMn_3+x (0 ≤ x ≤ 0.6)

The thermal expansion and magnetic properties of antiperovskite manganese nitrides Ag_1−xNMn_3+x were reported. The substitution of Mn for Ag effectively broadens the temperature range of negative thermal expansion and drives it to cryogenic temperatures. As x increases, the paramagnetic (PM) to antiferromagnetic (AFM) phase transition temperature decreases. At x ∼ 0.2, the PM-AFM transition overlaps with the AFM to glass-like state transition. Above x = 0.2, two new distinct magnetic transitions were observed: One occurs above room temperature from PM to ferromagnetic (FM), and the other one evolves at a lower temperature (T^*) below which both AFM and FM orderings are involved. Further, electron spin resonance measurement suggests that the broadened volume change near T^* is closely related with the evolution of Γ^5g AFM ordering.