Negative thermal expansion in YbMn2Ge2 induced by the dual effect of magnetism and valence transition
Yongqiang Qiao, Yuzhu Song, Andrea Sanson, Longlong Fan, Qiang Sun, Shu‐Xian Hu, Lunhua He, Hongjie Zhang, Xianran Xing, Jun Chen
Abstract
Abstract Negative thermal expansion (NTE) is an intriguing property, which is generally triggered by a single NTE mechanism. In this work, an enhanced NTE ( α v = −32.9 × 10 −6 K −1 , Δ T = 175 K) is achieved in YbMn 2 Ge 2 intermetallic compound to be caused by a dual effect of magnetism and valence transition. In YbMn 2 Ge 2 , the Mn sublattice that forms the antiferromagnetic structure induces the magnetovolume effect, which contributes to the NTE below the Néel temperature (525 K). Concomitantly, the valence state of Yb increases from 2.40 to 2.82 in the temperature range of 300–700 K, which simultaneously causes the contraction of the unit cell volume due to smaller volume of Yb 3+ than that of Yb 2+ . As a result, such combined effect gives rise to an enhanced NTE. The present study not only sheds light on the peculiar NTE mechanism of YbMn 2 Ge 2 , but also indicates the dual effect as a possible promising method to produce enhanced NTE materials.