Controllable negative thermal expansion in NaZn₁₃-type La(Fe, Co, Al)₁₃ compounds

Control of negative thermal expansion (NTE) is of great importance for various applications of NTE materials. Here, we report an effective way to control both the coefficient of thermal expansion (CTE) and NTE temperature-window in NaZn13-type La(Fe, Co, Al)(13) compounds by Al and Co substitutions. Experiments show that the average CTE decreases with the increase in Al content. Besides, the NTE temperature-window shifts toward higher temperature due to Co doping. Further studies of magnetic characterizations reveal that the CTE is strongly correlated with the square of the spontaneous magnetization M-s(2)(T). Moreover, the NTE temperature-window is influenced by the density of 3d electrons at the Fermi level and the Fe-I-Fe-II magnetic exchange interactions. This effective way demonstrated in this work to achieve controllable NTE indicates the potentials in practical applications for NTE materials.