MnNiSi系統合金係因磁熱效應和結構轉變受到了極大之關注，並且可通過一階磁結構耦合，在室溫下產生巨大的磁熱效應。在本篇研究中，因MnNiSi合金作為多功能之磁熱材料，本實驗藉由改變其合金之元素組成比例，探討其應用之研究發展。
MnNiSi合金本身為正交結構相，其相轉變溫度在約1223K，在極高溫度下表現出結構轉變，其居禮溫度約為622K。因此，MnNiSi合金無法自行實現MST，為了使MST實現以實現室溫磁製冷，應大幅度降低相轉變溫度。本實驗利用配置比例不同導致元素之缺陷空位，期望透過微量的Si比例調整就能使MnNiSi合金展現出不同之性能。
為熔煉MnNiSi三元合金，實驗使用真空感應熔煉爐熔煉樣品，且以添加99.99%高純度Mn、Ni和Si金屬，配置MnNiSi 添加2%、3%和4%的Si元素以及MnNiSi添加1%、2%和3%的Ni元素，所得到合金成分組成比例，利用場發射掃描式電子顯微鏡(SEM)、X光繞射儀(XRD)分析。因元素間之熔點不一致，真空感應熔煉爐容易導致熔煉過程會有揮發現象，而發現合金之元素分佈不均且有偏析相之產生。在MnNiSi(MnNi1.03Si0.79)合金中，可在表面明顯觀察到MnNiSi合金顯示出有大面積之淺色區塊，而所測量之晶體結構顯示出相較比例1:1:1之MnNiSi多出了繞射角度2θ=37.5°、42.4°、44.8°和45.3°的繞射峰，證實該偏析相為MnNi1.11Si0.89。而在MnNiSi+2%Si (MnNi1.03Si1.02)合金中，有深色偏析相結構之析出，可發現該相結構整體基材為Si0.34Mn0.33Ni0.33之合金相，而小部分面積為細長狀的深色Mn4.2Ni0.8Si3 偏析相，其晶體結構相較於等莫耳比之MnNiSi合金多出了位於2θ=44.5°的繞射峰。
本實驗透過採用MnNi1-xSix系列合金，研究其表面特徵及晶體結構，而實驗出之樣品再現性和穩定性皆不佳，可能會造成合金之結構轉變溫度和居禮溫度的不同，導致結構上之變化，對於後續之實驗會有無法預期之影響。本實驗初始目的是為使MnNiSi合金更準確且更簡易能熔煉出一具備磁熱效應，經過一階磁結構耦合之磁相變材料，以為後續之實驗所預備。因此，未來之實驗會使用莫耳比例1:1:1之MnNiSi合金作為基材，以添加等結構合金應用於未來之磁製冷技術實行。

The MnNiSi system is attracted a lot of interest due to its magnetocaloric effect and structural transformation, and it can produce a huge magnetocaloric effect at room temperature through first-order magnetostructural coupling. The approach of magnetostructural coupling by tuning the structural and magnetic transitions for a giant magnetocaloric effect can to be design the best solid-state magnetic refrigerant.
The MnNiSi alloy is unable to achieve the magnetostructural coupling by itself. In order to apply the MnNiSi alloy in room temperature magnetic refrigeration technology, the phase transition temperature should be reduced significantly. In this experiment, it is expected that the MnNiSi alloy can exhibit different properties by adjusting the Si element ratio due to the defective vacancies of the elements in different configuration ratios.
In this study, the MnNiSi alloy is a multifunctional magnetothermal material, and its application is investigated by changing the elemental composition of the alloy. The experiments were conducted using a vacuum induction furnace to melt MnNiSi ternary alloy samples with 99.99% high purity Mn, Ni, and Si metals. The composition ratios of the alloys obtained by configuring MnNiSi with 2%, 3% and 4% of Si elements and MnNiSi with 1%, 2% and 3% of Ni elements were analyzed by Scanning Electron Microscope (SEM) and X-ray Diffractometer (XRD).
The inconsistent melting point between elements, vacuum induction furnace will easily lead to volatile phenomenon in the melting process. The elemental distribution of the alloy was found to be inhomogeneous and to produce deviated phases.
In the MnNiSi (MnNi1.03Si0.79) alloy, it can be observed that the crystal structure of the MnNiSi alloy shows more number of diffraction peaks with diffraction angles of 2θ=37.5°、42.4°、44.8° and 45.3° compared to the 1:1:1 ratio of MnNiSi, which confirms that the phase structure is MnNi1.11Si0.89. In the MnNiSi + 2%Si (MnNi1.03Si1.02) alloy, the phase structure was found to be Si0.34Mn0.33Ni0.33 for the base material as a whole, while the Mn4.2Ni0.8Si3 precipitated phase with a small area in elongated form, and its crystal structure showed an additional diffraction peak at compared to the MnNiSi alloy.
In this experiment, MnNi1-xSix alloy was used to investigate its surface characteristics and crystalline structure, but the reproducibility and stability of the experimental samples were not satisfactory. The purpose of this experiment is to make the subsequent experiments more accurate and easy to melt the MnNiSi alloy. Therefore, the future experiments will use MnNiSi alloy with a 1:1:1 Mohr ratio as the substrate for the magnetic refrigeration technology.

[1] C.L.Tan, G.F.Dong, L.Gao, J.H.Sui, Z.Y.Gao, W.Cai, "Microstructure, martensitic transformation and mechanical properties of Ni50Mn30Ga20−xCux ferromagnetic shape memory alloys," Journal of Alloys and Compounds, V. 538. 2012, pp. 1-4.
[2] N A Mezaal, K V Osintsev, T B Zhirgalova, "Review of magnetic refrigeration system as alternative to conventional refrigeration system," IOP Conf. Series: Earth and Environmental Science, V. 87. 2017.
[3] E. Warburg, "Magnetische Untersuchungen," Annalen der Physik, V. 249. 1881, pp. 141-164.
[4] Chen J-H, Poudel Chhetri T, Us Saleheen A, Young DP, Dubenko I, Ali N, et al., "Effects of heat treatments on magneto-structural phase transitions in MnNiSi-FeCoGe alloys," Intermetallics, V. 112. 2019.
[5] V.K. Pecharsky, K.A. Gschneidner Jr., "Attainment of temperatures below 1°absolute by demagnetization of Gd2(SO4)38H2O," Adv. Cryog. Eng., V.42A. 1997, p. 423.
[6] J. Glanz, "Making a bigger chill with magnets," Science,V. 279. 1998, pp. 2045.
[7] O. Tegus, E. Bruck, K.H.J. Buschow, F.R. de Boer, "Transition-metal-based magnetic refrigerants for room-temperature applications," Nature, V.415. 2002, pp. 150.
[8] Jinlong Wang, Jing Bai, Die Liu, Xinzeng Liang, Haile Yan, Yudong Zhang, Claude Esling, Xiang Zhao, Liang Zuo, "Understanding the magneto-structural coupling of Ni50Mn35.4In14.6 alloy from first-principles calculations," Journal of Magnetism and Magnetic Materials, V. 488. 2019.
[9] Díaz-García Á, Law JY, Moreno-Ramírez LM, Giri AK, Franco V, "Deconvolution of overlapping first and second order phase transitions in a NiMnIn Heusler alloy using the scaling laws of the magnetocaloric effect," Journal of Alloys and Compounds, V. 871. 2021.
[10] M. Almanza, A. Pasko, F. Mazaleyrat, M. LoBue, IEEE Transactions on Magnetics, V. 53. 2017.
[11] F. Scheibel, D. Spoddig, R. Meckenstock, T. Gottschall, A. Çakır, T. Krenke, M. Farle, O. Gutfleisch, and M. Acet, "Room-temperature five-tesla coercivity of a rare earth-free shell-ferromagnet," Applied Physics Letters, V. 110. 2017.
[12] Zhang D, Nie Z, Wang Z, Huang L, Zhang Q, Wang Y-d, "Giant magnetocaloric effect in MnCoGe with minimal Ga substitution," Journal of Magnetism and Magnetic Materials, V. 387. 2015, pp. 107-10.
[13] 李翊豪，國立中正大學碩士論文 (2001)
[14] M. Liu, W. Saman, F. Bruno, "Review on storage materials and thermal performance enhancement techniques for high temperature phase change thermal storage systems," Renew Sust Energy Rev, V. 16. 2012, pp. 2118-2132.
[15] Doktors der Naturwissenschaften, Fakultät für Physik der Universität, "Magnetic interactions in martensitic Ni-Mn based Heusler systems," S. Aksoy, 2010.
[16] V.K. Pecharsky, J.K.A. Gschneidner, "Giant magnetocaloric effect in Gd5 (Si2 Ge2), Physical Review Letters, V. 78. 1997, pp. 4494.
[17] J.D. Moore, K. Morrison, G.K. Perkins, D.L. Schlagel, T.A. Lograsso, K.A. Gschneidner Jr., V.K. Pecharsky, L.F. Cohen, "Metamagnetism seeded by nanostructural features of single-crystalline Gd5Si2Ge2, Adv. Mater., V. 21. 2009, pp. 3780.
[18] F.X. Hu, B.G. Shen, J.R. Sun, Z.H. Cheng, G.H. Rao, X.X. Zhang, "Influence of negative lattice expansion and metamagnetic transition on magnetic entropy change in the compound LaFe11.4Si1.6," Applied Physics Letters, V. 78. 2001, pp. 3675.
[19] J. Lyubina, K. Nenkov, L. Schultz, O. Gutfleisch, "Multiple metamagnetic transitions in the magnetic refrigerant La(Fe,Si)13Hx," Physical Review Letters, V. 101. 2008, pp. 177203.
[20] O. Tegus, E. Bruck, K.H.J. Buschow, F.R. de Boer, "Transition-metal-based magnetic refrigerants for room-temperature applications," Nature, V. 415. 2002, pp. 150.
[21] J. Liu, T. Gottschall, K.P. Skokov, J.D. Moore, O. Gutfleisch, "Giant magnetocaloric effect driven by structural transitions," Nature Materials, V. 11. 2012, pp. 620.
[22] O. Tegus, E. Brück, K.H.J. Buschow, F.R. de Boer, "Transition-metal-based magnetic refrigerants for room-temperature applications," Nature, V. 415. 2002, pp. 150
[23] GschneidnerJr KA, Pecharsky VK, Tsokol AO, "Recent developments in magnetocaloric materials," Reports on Progress in Physics, V. 68, No. 6. 2005, pp. 1479-539.
[24] H. Osterreicher, F.T. Parker, "Magnetic cooling near Curie temperature above 300K," Journal of Applied Physics, V. 55. 1984, pp. 4334-4338.
[25] T. Samanta, D.L. Lepkowski, A.U. Saleheen, A. Shankar, J. Prestigiacomo, I. Dubenko, A. Quetz, I.W.H. Oswald, G.T. McCandless, J.Y. Chan, P.W. Adams, D.P. Young, N. Ali, S. Stadler, "Hydrostatic pressure-induced modifications of structural transitions lead to large enhancements of magnetocaloric effects in MnNiSi-based systems," Physical Review B, V. 91 . 2015.
[26] Kamble, Deepak, "MnNiSi based magnetocaloric alloys for cooling and energy harvesting applications," Nanyang Technological University, 2019.
[27] Zhao Rong-bing, Zhao Yun-cai, "Thermodynamic analysis of phase transformation temperature affected by magnetic field on nickel-base Ni-Mn-Ga ferromagnetic alloy," Nonferrous Materials Science and Engineering, V. 3. 2012.
[28] L. Lei, Z. G. Zheng, S. Jin, W. H. Wang, C. F. Li, J. Y. Liu, Z. G. Qiu, D. C. Zeng, "The magnetostructural transition and magnetocaloric properties in Fe0.6Mn0.4NiSi1−xAlx alloys," Journal of Applied Physics, V. 128. 2020.
[29] A. Aryal, A. Quetz, S. Pandey, M. Eubank, T. Samanta, I. Dubenko, S. Stadler, N. Ali, "Phase diagram and magnetocaloric effects in Ni1-xCrxMnGe1.05," Journal of Applied Physics, V. 117. 2015, pp. 17A711.
[30] E.K. Liu, H. Zhang, G.Z. Xu, X.M. Zhang, R.S. Ma, W.H. Wang, J.L. Chen, H.W. Zhang, G.H. Wu, L. Feng, X.X. Zhang, "Giant magnetocaloric effect in isostructural MnNiGe-CoNiGe system by establishing a Curie-temperature window," Applied Physics Letters, V. 102. 2013, pp. 122405.
[31] C. Zhang, D. Wang, Q. Cao, S. Ma, H. Xuan, Y. Du, "The magnetostructural transformation and magnetocaloric effect in Co-doped MnNiGe1.05 alloys," Journal of Applied Physics, V. 43. 2010, pp. 205003.
[32] A. Quetz, B. Muchharla, T. Samanta, I. Dubenko, S. Talapatra, S. Stadler, N. Ali, "Phase diagram and magnetocaloric effects in Ni50Mn 35(In1-xCrx)15 and (Mn 1-xCrx)NiGe1.05 alloys," Journal of Applied Physics, V. 115. 2014, pp. 17A922.
[33] Y.G. Shi, L.S. Xu, X.G. Zhou, Z.Y. Chen, T.F. Zheng, D.N. Shi, "Magnetostructural phase transition in Ga-doped MnNiGe compounds," Physics Status Solidi A, V. 210. 2013, pp. 2575.
[34] T. Samanta, I. Dubenko, A. Quetz, S. Temple, S. Stadler, N. Ali, "Magnetostructural phase transitions and magnetocaloric effects in MnNiGe 1-xAl x," Applied Physics Letters, V. 100. 2012, pp. 52404.
[35] E. Liu, Y. Du, J. Chen, W. Wang, H. Zhang, G. Wu, "Magnetostructural transformation and magnetoresponsive properties of MnNiGe1-xSnx alloys," IEEE Transactions on Magnetics, V. 47. 2011, pp. 4041.
[36] L. Lei, Z. G. Zheng, S. Jin, W. H. Wang, C. F. Li, J. Y. Liu, Z. G. Qiu, D. C. Zeng, "The magnetostructural transition and magnetocaloric properties in Fe0.6Mn0.4NiSi1−xAlx alloys," Journal of Applied Physics, V. 128. 2020.
[37] W. Bażela, A. Szytuła, J. Todorović, A. Zięba, "Crystal and magnetic structure of the NiMnGe1−nSin System," Physics Status Solidi, V. 64. 1981, pp. 367-378.
[38] E.K. Liu, W.H. Wang, L. Feng, W. Zhu, G.J. Li, J.L. Chen, H.W. Zhang, G.H. Wu, C.B. Jiang, H.B. Xu, F.R. de Boer, "Stable magnetostructural coupling with tunable magnetoresponsive effects in hexagonal ferromagnets," Nat. Commun., V. 3. 2012, pp. 873.
[39] G.J. Li, E.K. Liu, H.G. Zhang, Y.J. Zhang, J.L. Chen, W.H. Wang, H.W. Zhang, G.H. Wu, S.Y. Yu, "Phase diagram, ferromagnetic martensitic transformation and magnetoresponsive properties of Fe-doped MnCoGe alloys," Journal of Magnetism and Magnetic Materials, V. 332. 2013, pp. 146-150.
[40] Samanta T, Lloveras P, Us Saleheen A, Lepkowski DL, Kramer E, Dubenko I, et al., "Barocaloric and magnetocaloric effects in (MnNiSi)1−x(FeCoGe)x," Applied Physics Letters, V. 112, No. 2. 2018.
[41] C.L. Zhang, D.H. Wang, Z.D. Han, B. Qian, H.F. Shi, C. Zhu, J. Chen, T.Z. Wang, "The tunable magnetostructural transition in MnNiSi-FeNiGe system," Applied Physics Letters, V. 103. 2013, pp. 132411.
[42] J. Liu, Y.Y. Gong, G.Z. Xu, G. Peng, Ishfaq Ahmad Shah, Najamul Hassan, F. Xu, "Realization of magnetostructural coupling by modifying structural transitions in MnNiSi-CoNiGe system with a wide Curie-temperature window," Science Reports, V. 6. 2016, pp. 23386.
[43] T. Samanta, D.L. Lepkowski, A.U. Saleheen, A. Shankar, J. Prestigiacomo, I. Dubenko, A. Quetz, I.W.H. Oswald, G.T. McCandless, J.Y. Chan, P.W. Adams, D.P. Young, N. Ali, S. Stadler, "Effects of hydrostatic pressure on magnetostructural transitions and magnetocaloric properties in (MnNiSi)1-x(FeCoGe)x," Journal of Applied Physics, V.117. 2015, pp. 123911.
[44] Law JY, Moreno-Ramírez LM, Díaz-García Á, Martín-Cid A, Kobayashi S, Kawaguchi S, et al., "MnFeNiGeSi high-entropy alloy with large magnetocaloric effect," Journal of Alloys and Compounds, V. 855. 2021.
[45]J.Liu, K.Skokov, O.Gutfleisch, "Magnetostructural transition and adiabatic temperature change in Mn–Co–Ge magnetic refrigerants," Scripta Materialia, V. 66. 2012, pp. 642-645.
[46] 薛正良，李正邦，張家雯，高銀露, 用氧化鈣坩堝真空感應熔煉超低氧鋼的去氧動力學(2003)
[47] Li Y, Wei ZY, Liu EK, Liu GD, Luo HZ, Xi XK, et al., "Coupled Magnetic and Structural Transitions in Fe-Doped MnNiSi Compounds," IEEE Transactions on Magnetics, V. 51, No. 11. 2015, pp. 1-4.
[48] Biao Hu, Honghui Xu, Shuhong Liu, Yong Du, Cuiyun He, Chunsheng Sha, Dongdong Zhao, Yingbiao Peng, "Experimental investigation and thermodynamic modeling of the Mn–Ni–Si system," Calphad, V. 35. 2011, pp. 346-354.
[49] Jun-LiangLiu, Yan-CongChen, Fu-ShengGuo, Ming-LiangTong, "Recent advances in the design of magnetic molecules for use as cryogenic magnetic coolants," Coordination Chemistry Reviews, V. 281. 2014, pp. 26-49.
[50] Pal SK, Frommen C, Kumar S, Hauback BC, Fjellvåg H, Helgesen G, "Enhancing giant magnetocaloric effect near room temperature by inducing magnetostructural coupling in Cu-doped MnCoGe," Materials & Design, V. 195. 2020.
[51] A. Diestel, R. Niemann, B. Schleicher, S. Schwabe, L. Schultz, S. Fähler, "Field temperature phase diagrams of freestanding and substrate-constrained epitaxial Ni-Mn-Ga-Co films for magnetocaloric applications," Journal of Applied Physics, V.118. 2015), pp. 023908-023919.