Doping effect of Co at Ag sites in antiperovskite Mn₃AgN compounds

Antiperovskite compounds Mn₃Ag_1-xCo_xN (x = 0.2, 0.5 and 0.8) are synthesized and the doping effect of the magnetic element Co at the Ag site is investigated. The crystal structure is not changed by the introduction of Co. However, with the increase of the content of Co, the spin reorientation gradually disappears and the antiferromagnetic transition changes to the ferromagnetic transition at the elevated temperature when x = 0.8. In addition, all of the magnetic phase transitions at the elevated temperature are always accompanied by the abnormal thermal expansion behaviors and an entropy change. Moreover, when x = 0.8, the coefficient of linear expansion is -1.89 × 10^-6K^-1 (290-310 K, δT = 20 K), which is generally considered as the low thermal expansion.