Thermophysical properties of the intermetallic Mn3MN perovskites II. Heat capacity of manganese zinc nitride: Mn3ZnN and manganese gallium nitride: Mn3GaN

Abstract

Heat-capacity measurements from 5 to 345 K for Mn3ZnN and Mn3GaN are here reported. When one lowers the temperature Mn3ZnN shows two anomalies: the first at TN = (191.4±0.1) K, sharp and narrow, and the second at TA = (127.5±0.1) K. The transitions are due to magnetic ordering and lattice expansion, and to magnetic re-ordering and lattice contraction, respectively. Moreover, both transitions have first-order character. Mn3GaN shows only one anomaly at TN = (278.5±0.1) K, sharp and narrow, due to the magnetic ordering and an abrupt lattice contraction. The equilibrium molar thermodynamic properties at 298.15 K are Cp,m/RSm∘(T)/R{Hm∘(T)−Hm∘(0)}/RK−{Gm∘(T)−Hm∘(0)}/RTMn2ZnN14.5618.8782992.78.841Mn3GaN14.8418.7722965.28.827The analysis of the results below 10 K yields the low-temperature electronic coefficients: γ = (0.022±0.001) J·K−2·mol−1 for Mn3ZnN and γ = (0.038±0.002) J·K−2·mol−1 for Mn3GaN. The existence of a variation in γ in the transition at TA for the Zn compound is clearly derived. For the Ga compound no γ change was detected, but an anomalous electronic contribution was noted.