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arXiv 1408.3201cond-mat.mtrl-sci
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CrN磁性相结构稳定性和热力学的从头算和实验研究

Structural stability and thermodynamics of CrN magnetic phases from ab initio and experiment

Liangcai Zhou, David Holec, Matthias Bartosik, Fritz Körmann, Blazej Grabowski, Jörg Neugebauer, Paul H. Mayrhofer

摘要:

采用第一性原理密度泛函理论(DFT)加U方法结合热膨胀的实验测量,对化学计量比化合物CrN的动力学和热力学相稳定性(包括不同的结构和磁性构型)进行了全面的研究.比较DFT和DFT+U的结果与实验数据表明,电子关联的处理,使用标准DFT以外的方法是至关重要的。非磁性的面心立方B1-CrN相是弹性和动态不稳定的,即使在高压下,而非零局部磁矩的CrN相预测是动态稳定的DFT+U计划的框架内。此外,不同的处理的交换相关(xc)功能的影响进行所有的计算采用局部密度近似和广义梯度近似。为了解决有限的温度特性,无论是,磁和振动的自由能的贡献已计算采用我们最近开发的自旋空间平均方法。低温反铁磁和高温顺磁(PM)CrN变体之间的计算相变温度与实验值非常吻合,并揭示了XC-功能的选择的强烈影响。采用晶片曲率法从反应磁控溅射沉积的具有致密膜形貌的单相B1-CrN薄膜中实验测定了CrN的线性热膨胀系数随温度的变化。PM B1-CrN的线性热膨胀系数的实验值与从头计算值吻合较好。其他的热力学性质,如比热容,已计算以及与以前的实验数据进行比较。

英文摘要:

The dynamical and thermodynamic phase stabilities of the stoichiometric compound CrN including different structural and magnetic configurations are comprehensively investigated using a first-principles density-functional-theory (DFT) plus U approach in conjunction with experimental measurements of the thermal expansion. Comparing DFT and DFT+U results with experimental data reveals that the treatment of electron correlations using methods beyond standard DFT is crucial. The non-magnetic face-centered cubic B1-CrN phase is both, elastically and dynamically unstable, even under high pressure, while CrN phases with non-zero local magnetic moments are predicted to be dynamically stable within the framework of the DFT+U scheme. Furthermore, the impact of different treatments for the exchange-correlation (xc)-functional is investigated by carrying out all computations employing the local density approximation and generalized gradient approximation. To address finite-temperature properties, both, magnetic and vibrational contributions to the free energy have been computed employing our recently developed spin-space averaging method. The calculated phase transition temperature between low-temperature antiferromagnetic and high-temperature paramagnetic (PM) CrN variants is in excellent agreement with experimental values and reveals the strong impact of the choice of the xc-functional. The temperature-dependent linear thermal expansion coefficient of CrN is experimentally determined by the wafer curvature method from a reactive magnetron sputter deposited single-phase B1-CrN thin film with dense film morphology. A good agreement is found between experimental and ab initio calculated linear thermal expansion coefficients of PM B1-CrN. Other thermodynamic properties, such as the specific heat capacity, have been computed as well and compared to previous experimental data.

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