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利用实验测量和理论计算相结合的方法,研究了介于B2结构CoFe低有序合金和L21结构Co2FeSi高有序合金之间的Co50Fe50-xSix合金的结构相变、磁相变、分子磁矩和居里温度.采用考虑Coulomb相互作用的广义梯度近似(GGA+U)方法计算了合金的能带结构.研究发现,合金出现较强的原子有序倾向,表现出较强的共价成相作用.合金的晶格常数、磁矩、居里温度随Si含量的增加而线性地降低,极限成分Co2FeSi合金的分子磁矩和居里温度分别达到5.92B和777 ℃.原子尺寸效应导致合金晶格发生变化,但并未成为居里温度和分子磁矩变化的主导因素.分子磁矩的变化符合Slater-Pauling原理,但发现原子磁矩的变化并非线性,据此提出了共价成相对磁性影响的观点.采用Stearns理论解释了居里温度的变化趋势,排除了原子间距对居里温度的主导影响作用.能带计算的结果还表明,Co2FeSi作为半金属材料并非十分完美,可能在实际应用中会出现自旋极化率降低的问题.发现该系列合金的结构相变和磁相变随着成分的变化聚集在窄小的成分和温度范围内.The structural and the magnetic properties of Co50Fe50-xSix alloys are investigated by carrying out experimental measurements and electron structure calculation. The alloy series exhibits the highly chemical ordering structure, showing a strong covalent bonding effect. The lattice parameters, molecular moment and Curie temperature linearly decrease with the increase of the Si content. The deviation of the structure is attributed to the atomic size effect. Based on Stearns theories, the decrease of the itinerant 3d (di) electron results in the decrease of Curie temperature due to the substitution of Si for Fe. The change of molecular moment follows the Slater-Pauling rule, but the calculation indicates that the change of the atomic moments is not linear. It implies that the covalent bonding effect is responsible for the magnetic changes. The molecular moment and Curie temperature of Heusler alloy Co2FeSi are measured to be 5.92 B and 777 ℃, respectively. The calculation results also indicate that the half-metallic property of Co2FeSi may not be so perfect as reported, which requires a new design of energy band for the practical application. The investigation also shows that the structural transition and the magnetic structure transition accumulate in a narrow interval of Si content, which may become a good object for studying the interaction between the magnetization and the structure.
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Keywords:
- magnetic properties /
- Heusler alloys /
- structural phase transition
[1] Wurmehl S, Fecher G H, Kandpal H C, Ksenofontov V, Felser C, Lin H J 2006 Appl. Phys. Lett. 88 032503
[2] [3] Nakatani T M, Rajanikanth A, Gercsi Z, Takahashi Y K, Inomata K, Hono K 2007 J. Appl. Phys. 102 033916
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[8] [9] Okamoto H, Subramanian P R, Kacprzak L 2000 Desk Handbook Phase Diagrams for Binary Alloys (Vol. 2) (Ohio: ASM International) p1186
[10] [11] Dai D S, Qian K M 1987 Ferromagnetism (Vol. 1) (Beijing: Science Press) p105 (in Chinese) [戴道生、钱昆明 1987 铁磁学(上卷)(北京:科学出版社) 第105页]
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[14] Huang K, Han R Q 1988 Solid State Physics (Beijing: Higher Education Press) p417 (in Chinese) [黄 昆、韩汝琦 1988 固体物理 (北京:高等教育出版社) 第417页]
[15] [16] Stearns M B 1973 Phys. Rev. B 8 4383
[17] [18] [19] Stearns M B, Norbeck J M 1979 Phys. Rev. B 20 3739
[20] Buschow K H J, van Engen P G, Jongebreur R 1983 J. Magn. Magn.Mater. 38 1
[21] [22] Wurmehl S, Fecher G H, Kandpal H C, Ksenofontov V, Felser C, Lin H J, Morais J 2005 Phys. Rev. B 72 184434
[23] [24] O'handley R C 1999 Modern Magnetic Materials:Principles and Applications (Vol. 2) (New York: A Wiley-Interscience Publication) p144
[25] [26] Kbler J, William A R, Sommers C B 1983 Phys. Rev. B 28 1745
[27] [28] Qi J S, Yu H L, Jiang X F, Shi D N 2010 Int. J. Mod. Phys. B 24 967
[29] [30] [31] Zhao J J, Qi X, Liu E K, Zhu W, Li G J, Wang W H, Wu G H 2011 Acta Phys. Sin. 60 047108 (in Chinese) [赵晶晶、祁 欣、刘恩克、朱 伟、钱金凤、李贵江、王文洪、吴光恒 2011 60 047108]
[32] Balke B, Fecher G H, Felser C 2007 Appl. Phys. Lett. 90 242503
[33] -
[1] Wurmehl S, Fecher G H, Kandpal H C, Ksenofontov V, Felser C, Lin H J 2006 Appl. Phys. Lett. 88 032503
[2] [3] Nakatani T M, Rajanikanth A, Gercsi Z, Takahashi Y K, Inomata K, Hono K 2007 J. Appl. Phys. 102 033916
[4] [5] Eguchi T, Matsuda H, Oki K 1968 IEEE Trans. Magn. 4 476
[6] [7] Hanlumyuang Y, Ohodnicki P R, Laughlin D E, McHenry M E 2006 J. Appl. Phys. 99 08F101
[8] [9] Okamoto H, Subramanian P R, Kacprzak L 2000 Desk Handbook Phase Diagrams for Binary Alloys (Vol. 2) (Ohio: ASM International) p1186
[10] [11] Dai D S, Qian K M 1987 Ferromagnetism (Vol. 1) (Beijing: Science Press) p105 (in Chinese) [戴道生、钱昆明 1987 铁磁学(上卷)(北京:科学出版社) 第105页]
[12] [13] Webster P J 1969 Contemp. Phys. 10 559
[14] Huang K, Han R Q 1988 Solid State Physics (Beijing: Higher Education Press) p417 (in Chinese) [黄 昆、韩汝琦 1988 固体物理 (北京:高等教育出版社) 第417页]
[15] [16] Stearns M B 1973 Phys. Rev. B 8 4383
[17] [18] [19] Stearns M B, Norbeck J M 1979 Phys. Rev. B 20 3739
[20] Buschow K H J, van Engen P G, Jongebreur R 1983 J. Magn. Magn.Mater. 38 1
[21] [22] Wurmehl S, Fecher G H, Kandpal H C, Ksenofontov V, Felser C, Lin H J, Morais J 2005 Phys. Rev. B 72 184434
[23] [24] O'handley R C 1999 Modern Magnetic Materials:Principles and Applications (Vol. 2) (New York: A Wiley-Interscience Publication) p144
[25] [26] Kbler J, William A R, Sommers C B 1983 Phys. Rev. B 28 1745
[27] [28] Qi J S, Yu H L, Jiang X F, Shi D N 2010 Int. J. Mod. Phys. B 24 967
[29] [30] [31] Zhao J J, Qi X, Liu E K, Zhu W, Li G J, Wang W H, Wu G H 2011 Acta Phys. Sin. 60 047108 (in Chinese) [赵晶晶、祁 欣、刘恩克、朱 伟、钱金凤、李贵江、王文洪、吴光恒 2011 60 047108]
[32] Balke B, Fecher G H, Felser C 2007 Appl. Phys. Lett. 90 242503
[33]
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