Effects of magnetic doping and temperature dependence of phonon dynamics in CaFe 1 − x Co x AsF compounds ( x = 0 , 0.06, and 0.12)
Effects of magnetic doping and temperature dependence of phonon dynamics in CaFe 1 − x Co x AsF compounds ( x = 0 , 0.06, and 0.12)
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DOI：
10.1103/physrevb.79.214514
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发表时间：
2009-04
影响因子：
3.7
通讯作者：
R. Mittal;R. Mittal;M. Zbiri;S. Rols;Yixi Su;Yinguo Xiao;Helmut Schober;S. Chaplot;Mark A. John
中科院分区：
文献类型：
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作者：
R. Mittal;R. Mittal;M. Zbiri;S. Rols;Yixi Su;Yinguo Xiao;Helmut Schober;S. Chaplot;Mark A. John
本文详细测量了CaFe1-x CoxAsF(x=0，0.06，0.12)系列FeAs化合物的声子态密度随温度的变化。用飞行时间IN4C和IN6能谱仪测量了CaFe1-xCoxASF(x=0，0.06，0.12)化合物的声子谱组成及其与温度的关系。300K下的声子谱比较表明，与母体CaFeAsF相比，掺杂化合物的声学声子模硬化高达12 meV。而在12%Co掺杂的CaFeAsF化合物中，从15 meV到25 meV的中能声子模也向高能方向移动。CaFe1-xCoxAsF(x=0，0.06，0.12)的实验结果与我们以前对母体和超导MFe2As2(M=Ba，Ca，Sr)的声子研究结果有很大不同，在这些化合物中，低能声学声子模不与掺杂反应，而在15-25K的中间范围内声子谱被软化。我们认为，较强的自旋声子相互作用对这些化合物中超导电性的出现起着重要作用。用从头算和壳层模型声子计算研究了CaFe1-xCoxASF(x=0，0.06，0.12)化合物的晶格动力学。我们发现，CaFeAsF化合物中Ca和Fe-As层之间相互作用的性质与我们以前对CaFe2As2的研究有很大的不同。
We report detailed measurements of composition as well as temperature dependence of the phonon density-of-states in a new series of FeAs compounds with composition CaFe1\_{1-x}Co\_{x}AsF (x = 0, 0.06, 0.12). The composition as well as temperature dependence of phonon spectra for CaFe\_{1-x}Co\_{x}AsF (x = 0, 0.06, 0.12) compounds have been measured using time of flight IN4C and IN6 spectrometers at ILL, France. The comparison of phonon spectra at 300 K in these compounds shows that acoustic phonon modes up to 12 meV harden in the doped compounds in comparison to the parent CaFeAsF. While intermediate energy phonon modes from 15 meV to 25 meV are also found to shift towards high energies only in the 12 % Co doped CaFeAsF compound. The experimental results for CaFe\_{1-x}Co\_{x}AsF (x = 0, 0.06, 0.12) are quite different from our previous phonon studies on parent and superconducting MFe2As2 (M=Ba, Ca, Sr) where low-energy acoustic phonon modes do not react with doping, while the phonon spectra in the intermediate range from 15 to 25 K are found to soften in these compounds. We argue that stronger spin phonon interaction play an important role for the emergence of superconductivity in these compounds. The lattice dynamics of CaFe\_{1-x}Co\_{x}AsF (x = 0, 0.06, 0.12) compounds is also investigated using the ab-initio as well as shell model phonon calculations. We show that the nature of the interaction between the Ca and the Fe-As layers in CaFeAsF compounds is quite different compared with our previous studies on CaFe2As2.