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对等价电子数组元Heusler合金Fe2RuSi的原子占位、电子结构与磁性进行了理论与实验研究. 第一性原理计算表明, 虽然Fe2RuSi中Fe, Ru均有8个价电子, 但是Ru仍表现出强烈的占据A, C晶位倾向. 基态总能最低的是Fe与Ru分别占据A, C晶位的XA结构, 次低的是Fe, Ru在A, C位混乱占位的L21B结构, 且两者能量差很小. 这说明决定Heusler 合金中过渡族原子占位的因素除价电子数以外还可能有原子半径和共价杂化作用等. 态密度和差分电荷密度计算表明Heusler合金中主族元素与最近邻过渡族元素之间的p-d共价杂化对Heusler合金的占位有明显影响, 在XA结构中Ru与Si和Fe (B)之间都存在明显的杂化作用, 而在高能的L21结构中, Si与最近邻的Fe 杂化作用相当弱. XRD测试表明在室温Fe2RuSi存在A, C位之间的Fe-Ru反占位, 形成了能量次高的L21B结构, 这主要来自于混合熵对自由能的贡献及其引起的原子自发混乱占位. 在5 K下Fe2RuSi的饱和磁矩为4.87 B/f.u., 与计算值符合得相当好.The site preference, electronic structure, and magnetism of Heusler alloy Fe2RuSi are investigated theoretically and experimentally. The magnetic and electronic properties of Heusler alloys are strongly related to the atomic ordering and site preference in them. Usually, the site preference of the transition metal elements is determined by the number of their valence electrons. However, the recent results suggest that some new possible factors such as atomic radius should also be considered. Here we compare the phase stabilities of several different atomic orderings like XA, L21, DO3, L21B in Fe2RuSi, in which Fe and Ru atom have 8 valence electrons each, thus the influence of number of their valence electrons can be omitted. First-principles calculations suggest that Ru atom prefers entering sites A and C in the lattice. In ground state, the most stable structure is of XA type, in which Fe and Ru atoms occupy A and C sites, respectively and the second stable structure is L21B type, in which Fe and Ru atoms occupy A and C sites randomly. With Ru atom entering into the B site, the total energy increases rapidly. Thus there is still a strongly preferable occupation of Ru though Fe and Ru atom are isoelectronic. This confirms that the valence electrons rule may be not enough to determine the site preference of the transition metal element in Heusler alloy. The preferable occupation of Ru atom in Fe2RuSi can be explained from the electronic structure. It is found that in the XA DOS, there is strong hybridization between the electrons of the nearest Ru and Si or Fe (B) atom. However, in the high energy L21 structure the hybridization between Ru and the nearest Fe (A, C) is weak, which reduces its phase stability. This is confirmed further by the charge density difference calculation. Single phase Fe2RuSi with a lattice parameter of 5.79 is synthesized successfully. Comparing the superlattice reflections (111) and (200) in the experimental XRD pattern with those in the simulated patterns for different structures, we find that Fe2RuSi crystallizes in L21B structure rather than the most stable XA one at room temperature, which mainly originates from the contribution of mixed entropy to the free energy, and its caused atomic disorder at high temperatures. This disorder can be retained during the cooling procedure, while it does not influence the conclusion that Ru atom prefers the (A, C) sites in Fe2RuSi strongly. Finally, the saturation magnetization Ms at 5 K is 4.87 B/f.u., which agrees well with the theoretical result. The large total magnetic moment mainly comes from the contributions of Fe, especially Fe magnetic moments on B sites.
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Keywords:
- Heusler alloy /
- Fe2RuSi /
- electronic structure /
- site preference
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[2] Liu X H, Lin J B, Liu Y H, Jin Y J 2011 Acta Phys. Sin. 60 107104 (in Chinese) [刘新浩, 林景波, 刘艳辉, 金迎九 2011 60 107104]
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[16] Endo K, Kanomata T, Nishihara H, Ziebeck K R A 2012 J. Alloys Compd. 510 1
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[19] Zhang H, Xiao M Z, Zhang Y G, Lu G X, Zhu S L 2011 Acta Phys. Sin. 60 026103 (in Chinese) [张辉, 肖明珠, 张国英, 路广霞, 朱圣龙 2011 60 026103]
[20] Feng Y, Rhee J Y, Wiener T A, Lynch D W, Hubbard B E, Sievers A J, Schlagel D L, Lograsso T A, Miller L L 2001 Phys. Rev. B 63 165109
[21] Kreiner G, Kalache A, Hausdorf S, Alijani V, Qian J F, Shan G C, Burkhardt U, Ouardi S, Felser C 2014 Anorg. Allg. Chem. 640 738
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[1] de Groot R A, Mueller F M, van Engen P G, Buschow K H J 1983 Phys. Rev. Lett. 50 2024
[2] Liu X H, Lin J B, Liu Y H, Jin Y J 2011 Acta Phys. Sin. 60 107104 (in Chinese) [刘新浩, 林景波, 刘艳辉, 金迎九 2011 60 107104]
[3] Sakuraba Y, Izumi K, Iwase T, Bosu S, Saito K, Takanashi K, Miura Y, Futatsukawa K, Abe K, Shirai M 2010 Phys. Rev. B 82 094444
[4] Ullakko K, Huang J K, Kantner C, O'handley R C, Kokorin V V 1996 Appl. Phys. Lett. 69 1966
[5] Kainuma R, Imano Y, Ito W, Sutou Y, Morito H, Okamoto S, Kitakami O, Oikawa K, Fujita A, Kanomata T, Ishida K 2006 Nature 439 957
[6] Chadov S, Qi X, Kbler J, Fecher G H, Felser C, Zhang S C 2010 Nat. Mater. 9 541
[7] Ouardi S, Fecher G H, Felser C, Kbler J 2013 Phys. Rev. Lett. 110 100401
[8] Zhu W, Liu E K, Zhang C Z, Qin Y B, Luo H Z, Wang W H, Du Z W, Li J Q, Wu G H 2012 Acta Phys. Sin. 61 027502 (in Chinese) [朱伟, 刘恩克, 张常在, 秦元斌, 罗鸿志, 王文洪, 杜志伟, 李建奇, 吴光恒 2012 61 027502]
[9] Kandpal H C, Fecher G H, Felser C 2007 J. Phys. D: Appl. Phys. 40 1507
[10] Luo H Z, Xin Y P, Liu B H, Meng F B, Liu H Y, Liu E K, Wu G H 2016 J. Alloys Compd. 665 180
[11] Kobayashi Y, Katada M, Sano H, Okada T, Asai K, Iwamoto M, Ambe F 1990 Hyperfine Interact. 54 585
[12] Kobayashi Y, Asai K, Okada T, Ambe F 1994 Hyperfine Interact. 84 131
[13] Vanderbilt D 1990 Phys. Rev. B 41 7892
[14] Clark S J, Segall M D, Pickard C J, Hasnip P J, Probert M J, Refson K, Payne M C 2005 Z. Kristallogr. 220 567
[15] Perdew J P, Burke K, Ernzerhof M 1996 Phys. Rev. Lett. 77 3865
[16] Endo K, Kanomata T, Nishihara H, Ziebeck K R A 2012 J. Alloys Compd. 510 1
[17] Gelatt C D, Williams A R, Moruzzi V L 1983 Phys. Rev. B 27 2005
[18] Wei Z Y, Liu E K, Chen J H, Li Y, Liu G D, Luo H Z, Xi X K, Zhang W, Wang W H, Wu G H 2015 Appl. Phys. Lett. 107 022406
[19] Zhang H, Xiao M Z, Zhang Y G, Lu G X, Zhu S L 2011 Acta Phys. Sin. 60 026103 (in Chinese) [张辉, 肖明珠, 张国英, 路广霞, 朱圣龙 2011 60 026103]
[20] Feng Y, Rhee J Y, Wiener T A, Lynch D W, Hubbard B E, Sievers A J, Schlagel D L, Lograsso T A, Miller L L 2001 Phys. Rev. B 63 165109
[21] Kreiner G, Kalache A, Hausdorf S, Alijani V, Qian J F, Shan G C, Burkhardt U, Ouardi S, Felser C 2014 Anorg. Allg. Chem. 640 738
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