Anomalous thermal expansion and enhanced magnetocaloric effect in <001>‐textured Mn x Fe 5– x Si 3 alloys

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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 Mn x Fe 5– x Si 3 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.

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