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arXiv 2109.03557cond-mat.mtrl-sci
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MnCoSi-based螺旋磁体中自旋旋转相干诱导的零热膨胀

Coherent spin rotation-induced zero thermal expansion in MnCoSi-based spiral magnets

Jun Liu, Bei Ding, Yuan Yao, Xuekui Xi, Zhenxiang Cheng, Jianli Wang, Chin-wei Wang, Guangheng Wu, Wenhong Wang

摘要:

表现出零热膨胀(ZTE)(即,在温度变化期间的体积不变性)的材料可以抵抗热冲击,并且在现代工业中高度期望作为高精度部件。然而,纯中兴材料是罕见的,特别是那些是金属。在这里,我们报告的纯金属中兴材料的发现:正交Mn 1-xNixCoSi螺旋磁铁。Ni的引入可以有效地增强MnCoSi基合金中的铁磁交换作用,并构建从螺旋磁态到类铁磁态的转变。系统的原位中子粉末衍射揭示了一种新的基态的bc平面的摆线螺旋磁结构,随着温度的升高,该结构将转变为ab平面的螺旋状。结合洛伦兹透射电子显微镜技术,摆线和螺旋自旋顺序相干旋转在不同的周期沿c轴在磁性转变。这种自旋旋转驱动耦合晶格的连续运动,并沿a轴诱导大的负热膨胀,最终导致宽温ZTE效应。我们的工作不仅介绍了一种新的ZTE合金,而且提出了一种新的机制,通过它来发现或设计ZTE磁体。

英文摘要:

Materials exhibiting zero thermal expansion (ZTE), namely, volume invariance during temperature change, can resist thermal shock and are highly desired in modern industries as high-precision components. However, pure ZTE materials are rare, especially those that are metallic. Here, we report the discovery of a pure metallic ZTE material: an orthorhombic Mn1-xNixCoSi spiral magnet. The introduction of Ni can efficiently enhance the ferromagnetic exchange interaction and construct the transition from a spiral magnetic state to a ferromagnetic-like state in MnCoSi-based alloys. Systematic in situ neutron powder diffraction revealed a new cycloidal spiral magnetic structure in bc plane at ground state which would transform to the helical spiral in the ab plane with increasing temperature. Combined with Lorentz transmission electron microscopy techniques, the cycloidal and helical spin order coherently rotated at varying periods along the c axis during the magnetic transition. This spin rotation drove the continuous movement of the coupled crystalline lattice and induced a large negative thermal expansion along the a axis, eventually leading to a wide-temperature ZTE effect. Our work not only introduces a new ZTE alloy but also presents a new mechanism by which to discover or design ZTE magnets.

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