First-principles investigations of atomic disorder effects on magnetic and structural instabilities in transition-metal alloys.
First-principles investigations of atomic disorder effects on magnetic and structural instabilities in transition-metal alloys.
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过渡金属合金中原子无序对磁性和结构不稳定性影响的第一性原理研究。
DOI：
10.1103/physrevb.52.188
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发表时间：
1995
期刊：
影响因子：
--
通讯作者：
Reddy
中科院分区：
文献类型：
--
作者：
Schröter;Ebert;Akai;Entel;Hoffmann;Reddy
在本文中，我们使用 Korringa-Kohn-Rostocker 能带结构方案中的相干势近似来研究原子无序对铁镍等过渡金属合金的磁性和晶体结构的影响。该方法允许在同样明确的基础上研究无序合金，就像研究相应的化学计量有序相一样。特别是，我们计算了 fcc ${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{Ni}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$ 的磁性和结构结合面，浓度接近临界浓度 x=0.65（对应于 Invar 合金） ${\mathrm{Fe}}_{65}$${\mathrm{Ni}}_{35}$，借助固定自旋矩方法。我们发现，当我们从${\mathrm{Fe}}_{60}$${\mathrm{Ni}}_{40}$（具有与非磁性状态相距1.0 mRy/原子）明确定义的磁性基态到非磁性${\mathrm{Fe}}_{75}$${\mathrm{Ni}}_{25}$时，基态磁性逐渐消失。根据 ${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{Ni}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$ 的磁相图，发生这种无序驱动的磁-非磁转变的临界浓度为 x\ensuremath{\approxeq}0.65\char21{}0.70。这些计算必须与有序 fcc ${\mathrm{Fe}}_{3}$Ni 的从头计算进行比较；这里磁性基态比非磁性态稳定 1.25 mRy。无序相和有序相的这种不同的磁性行为可以用统计学来解释。此外，根据 ${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{Ni}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$ 的结构相图，磁无序基态相对于富铁侧的马氏体 fcc\ensuremath{\rightarrow}bcc 转变是不稳定的。我们还借助有限温度波动理论计算了结合表面的温度演变。我们在接近 Invar 浓度 x=0.65 的面心立方相中发现了有趣的重入铁磁相变。
In this paper we use the coherent-potential approximation within the Korringa-Kohn-Rostocker band-structure scheme to investigate the influence of atomic disorder on magnetism and crystal structure of transition-metal alloys like iron-nickel. This method allows an investigation of disordered alloys on an equally well-defined basis as an investigation of corresponding stoichiometrically ordered phases. In particular we have calculated the magnetic and structural binding surfaces of fcc ${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{Ni}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$ for concentrations close to the critical concentration x=0.65 which corresponds to the Invar alloy ${\mathrm{Fe}}_{65}$${\mathrm{Ni}}_{35}$, with the help of the fixed-spin-moment method. We find that magnetism in the ground state gradually vanishes as we go from ${\mathrm{Fe}}_{60}$${\mathrm{Ni}}_{40}$, which has a well-defined magnetic ground state being separated from the nonmagnetic state by 1.0 mRy/atom, to ${\mathrm{Fe}}_{75}$${\mathrm{Ni}}_{25}$ which is nonmagnetic. The criical concentration for which this disorder driven magnetic-nonmagnetic transition occurs is x\ensuremath{\approxeq}0.65\char21{}0.70 in accordance with the magnetic phase diagram of ${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{Ni}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$. These calculations have to be compared with ab initio calculations for ordered fcc ${\mathrm{Fe}}_{3}$Ni; here the magnetic ground state is by 1.25 mRy more stable than the nonmagnetic state. This different magnetic behavior of disordered and ordered phases can be explained on statistical grounds. Furthermore, the magnetic disordered ground state is unstable with respect to a martensitic fcc\ensuremath{\rightarrow}bcc transition on the Fe-rich side in accordance with the structural phase diagram of ${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{Ni}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$. We have furthermore calculated the temperature evolution of the binding surfaces with the help of a finite-temperature fluctuation theory. We find interesting reentrant ferromagnetic phase transitions in the fcc phase close to the Invar concentration x=0.65.