Negative thermal expansion in (Sc,Ti)Fe induced by an unconventional magnetovolume effect

• Published in: Materials horizons 2020-01, Vol.7 (1), p.275-281
• Main Authors: Song, Yuzhu, Sun, Qiang, Xu, Meng, Zhang, Ji, Hao, Yiqing, Qiao, Yongqiang, Zhang, Shantao, Huang, Qingzhen, Xing, Xianran, Chen, Jun
• Format: Article
• Language: English
• ISSN: 2051-6347; 2051-6355
• DOI: 10.1039/c9mh01025d

Negative thermal expansion (NTE) has been found in some magnetic functional materials due to the magnetovolume effect (MVE), in which an order-to-disorder magnetic transition occurs. Here, we report an unconventional MVE which can induce the crossover from the common positive thermal expansion of the end members of ScFe 2 and TiFe 2 to the NTE in the solid solution of (Sc 1− x Ti x )Fe 2 ( x = 0.6, α V = −28.36 × 10 −6 K −1 , 125-205 K). The direct evidence of neutron powder diffraction and first-principles calculations discloses that the decrease of intrinsic magnetic moments at the Fe(2a) site results in the ferromagnetic transition from one to another, which causes a stronger negative contribution to thermal expansion than the conventional MVE. The pair distribution function analysis verifies that the decrease in the nearest distance of Fe(6h)-Fe(6h) lying in the ab plane results in the shrinkage of the a ( b ) axis. The analysis of anisotropic atomic displacement parameters excludes the phonon induced NTE mechanism. Furthermore, an intriguing zero thermal expansion has been found in Sc 0.55 Ti 0.45 Fe 2 (10-250 K). The present study provides an approach to achieve NTE or controllable thermal expansion, which may be used to enhance other magnetic-related effects, such as the magnetocaloric and barocaloric effect. A new type of ferromagnetic-to-ferromagnetic transition induces the crossover from common positive to negative thermal expansion in (Sc,Ti)Fe 2 .