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  Gong, Y.; Miao, X.F.; Samanta, T.; Taake, C.; Liu, J.; Qian, F.J.; Shao, Y.Y.; Zhang, Y.J.; Ren, Q.Y.; Caron, L.; Xu, F.: Anomalous thermal expansion and enhanced magnetocaloric effect in <001>-textured Mn_xFe_5-xSi₃ alloys. Rare Metals 43 (2024), p. 2263-2274

10.1007/s12598-023-02575-8

Abstract:
The development of zero and negative thermal expansion (i.e., ZTE and NTE) materials is of crucial importance to the control of undesirable thermal expansion for high-precision devices. In the present work, ZTE and NTE were obtained in directionally-solidified MnxFe5–xSi3 alloys with a strong <001> texture, in striking contrast to positive thermal expansion in their isotropic counterparts. Magnetometry and in-situ X-ray diffraction (XRD) measurements were performed to uncover the origin of the anomalous thermal expansion. Magnetic measurements indicate a strong easy-plane magnetocrystalline anisotropy in the textured samples, where the magnetic moments are aligned within the ab plane of the hexagonal structure. Temperature-dependent XRD on the x = 1 sample reveals a ZTE character in the ab plane that is coupled to a ferromagnetic transition. As a result, the macroscopic ZTE (~ 0.22 × 10–6 K−1) in the x = 1 sample can be attributed to the microscopic magneto volume effect within the ab plane, which is realized by the introduction of the <001>-textured microstructure. Besides, the competition between antiferromagnetic and ferromagnetic exchange coupling leads to NTE in textured x = 1.5 and 2 samples. Additionally, textured x = 1 sample displays enhanced magnetocaloric properties as compared to the conventional counterparts with randomly-oriented grains. Consequently, this work demonstrates a new strategy toward the exploration of anomalous thermal expansion properties as well as the enhancement of magnetocaloric properties for materials with a strong magnetocrystalline anisotropy.