arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2005.13901cond-mat.str-el
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立方GdCu化合物电磁性质的第一性原理研究

First-principles study of the electronic and magnetic properties of cubic GdCu compound

Vikas Kashid, Ersoy Şaşıoğlu, Gustav Bihlmayer, Alexander B. Shick, Stefan Blügel

摘要:

采用自旋密度泛函理论研究了体相GdCu(CsCl型)的结构、电子和磁性,其中高度局域化的$4f$轨道在LDA+ $U$和GGA+ $U$方法中得到了处理.使用共线以及自旋螺旋计算计算的GdCu的磁基态表现出C型反铁磁配置表示的自旋螺旋传播矢量$\mathbf{Q}=\frac{2π}{a}(\frac{1}{2},\frac{1}{2},0)$。从自洽的电子结构的有效海森堡哈密顿量的参数进行评估,并用于确定磁转变温度。在平均场和无规相近似下,用GGA+ $U$和LDA+ $U$密度泛函计算了立方GdCu的Néel温度,计算结果与实验测量值吻合较好.特别是,在光电子能谱实验中观察到的核心Gd $4f$能级移动的理论理解进行了详细研究。采用自洽约束无规相位近似,我们确定了局域$4f$电子之间的有效库仑相互作用(Hubbard $U$)的强度。我们发现,在DFT+ $U$中,GdCu中Gd- $4f$态相对于体Gd的位移对晶格参数的选择是敏感的。用DFT+ $U$方法以及Hubbard-1近似计算的$4f$能级位移与实验结果不一致。

英文摘要:

The structural, electronic, and magnetic properties of bulk GdCu (CsCl-type) are investigated using spin density functional theory, where highly localized $4f$ orbitals are treated within LDA+$U$ and GGA+$U$ methods. The calculated magnetic ground state of GdCu using collinear as well as spin spiral calculations exhibits a C-type antiferromagnetic configuration representing a spin spiral propagation vector $\mathbf{Q}=\frac{2π}{a}(\frac{1}{2},\frac{1}{2},0)$. The parameters of the effective Heisenberg Hamiltonian are evaluated from a self-consistent electronic structure and are used to determine the magnetic transition temperature. The estimated Néel temperature of the cubic GdCu using GGA+$U$ and LDA+$U$ density functionals within the mean field and random phase approximations are in good agreement with the experimentally measured values. In particular, the theoretical understanding of the experimentally observed core Gd $4f$ levels shifting in photoemission spectroscopy experiments is investigated in detail. By employing the self-consistent constrained random-phase approximation we determined the strength of the effective Coulomb interaction (Hubbard $U$) between localized $4f$ electrons. We find that, the shift of Gd-$4f$ states in GdCu with respect to bulk Gd within DFT+$U$ is sensitive to choice of lattice parameter. The calculations for $4f$-level shifts using DFT+$U$ methods as well as Hubbard-1 approximation are not consistent with the experimental findings.

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