Negative thermal expansion (NTE) has emerged as one of the intense research topics to meet the demands of the precision industry for compensating positive thermal expansion (PTE) properties. The adjustment of the NTE behavior is the key for tailoring thermal expansion. Chemical modification and the particle size effect have been regarded as effective means to tune the NTE behavior, and the crystallographic contribution is usually the upper limit of NTE. Here, we reported a new way to tune the NTE behavior involving lattice distortion that is dominated by the magnetic structure in hexagonal MnM′Ge-based (M′:Ni,Co) alloys. The achieved maximal linear NTE reached ΔL/L ∼ −23 690 × 10⁻⁶ ( = −121.5 × 10⁻⁶ K⁻¹) in a temperature interval as wide as ∼195 K (80–275 K) for Fe-doped MnNiGe alloys. This value was 3.3 times larger than that of the corresponding average crystallographical contribution and exceeded that of almost all NTE materials reported to date. Neutron powder diffraction and first-principles calculations were carried out. The results revealed that Fe-doped MnNiGe showed incommensurate cone-spiral magnetic ordering, and the lattice distortion during the phase transition was more significant than that of MnCoGeIn with linear ferromagnetic ordering. The larger lattice distortion favored the cleavage of the hexagonal phase along the c-axis. As a result, a texture effect along the (110) crystal plane occurred during the molding process, which greatly enhanced the amplitude of the isotropic in-plane linear NTE. The present study provides a new strategy for exploring adjustable NTE behaviors.

中文翻译：

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掺铁MnNiGe化合物中的锥螺旋磁序占主导地位的晶格畸变和巨大的负热膨胀

负热膨胀（NTE）已成为满足精密行业补偿正热膨胀（PTE）性能要求的一项重要研究课题。NTE行为的调整是定制热膨胀的关键。化学改性和粒度效应已被认为是调节NTE行为的有效手段，并且晶体学贡献通常是NTE的上限。在这里，我们报道了一种新的方法来调谐涉及晶格畸变的NTE行为，该行为主要由六方MnM'Ge基（M'：Ni，Co）合金中的磁性结构决定。所实现的最大线性NTE达到Δ大号/大号〜-23 690×10 ^-6（= -121.5×10 ^-6 ķ ^-1）对于掺铁的MnNiGe合金，其温度间隔最宽约195 K（80-275 K）。该值是相应平均晶体学贡献值的3.3倍，并且超过了迄今为止报道的几乎所有NTE材料的值。进行了中子粉末衍射和第一性原理计算。结果表明，掺铁的MnNiGe的锥螺旋形磁序不等，相变过程中的晶格畸变比带有线性铁磁序的MnCoGeIn晶格畸变大。较大的晶格畸变有利于六方相沿c的裂解-轴。结果，在模制过程中沿（110）晶面产生了织构效应，这大大增强了各向同性面内线性NTE的幅度。本研究提供了探索可调整的NTE行为的新策略。