The evolution of magnetic transitions, negative thermal expansion and unusual electronic transport properties in Mn₃Ag_xMn_yN

The antiperovskite compounds Mn₃Ag_xMn_yN with Ag vacancies and Mn doping at Ag site were synthesized and investigated. The introduction of Ag vacancies has a very small influence on magnetic transitions. However, the magnetic transitions at T_N (Néel temperature) and T_t (transition at lower temperature) gradually overlap with Mn doping accompanied by broadening of negative thermal expansion behavior. We also observed the nearly zero temperature coefficient of resistivity (NZ-TCR) behavior above magnetic order-disorder transition. The tunable TCR values from positive to negative could be achieved in Mn₃Ag_xMn_yN by reducing the contribution of (electron-phonon) e-p scattering in resistivity. Our results reveal the significance of e-p scattering for the evolution of TCR values, which could enrich the understanding of NZ-TCR behavior in antiperovskite manganese nitrides.