NEGATIVE THERMAL EXPANSION PHENOMENA OF Mn_3(Cu_(1-x)Ge_x)N

The metallic nitrides Mn3(Cu1�xGex)N were prepared by solid-state sintering in the pure nitrogen atmosphere at 1073 K. The X-ray diffraction analysis shows that all of the sintered poly- crystalline samples present an antiperovskite structure of Mn3CuN phase. The linear thermal expan- sions of compounds Mn3(Cu1�xGex)N (0.40≤ x ≤0.60) measured by using Michelson interferometer, exhibited negative thermal expansion near Neel temperature. With increase in the content of Ge, the temperature at which the negative thermal expansion occurred increases while the temperature range widens, but the thermal expansion coefficient decreases. The sample with x=0.60 presents negative thermal expansion in the region of 250-290 K (around 273 K), the linear expansion coefficient can reach to −65×10 �6 K �1 , shows a potential for practical application. The temperature dependence of the magnetization indicates that the negative thermal expansion behavior of Mn3(Cu1�xGex)N compounds occurs in the gradual transition from antiferromagnetic to paramagnetic state. The negative thermal expansion is caused by magnetovolume effect, originating from magnetic spin order disappearance and