论文标题
从头开始确定pyrochlore y $ _2 $ mn $ _2 $ o $ $ _7 $的磁基状态的确定
Ab initio determination of magnetic ground state of pyrochlore Y$_2$Mn$_2$O$_7$
论文作者
论文摘要
在y $ _ {2} $ Mn $ _ {2} $ o $ $ $ _ {7} $的磁接地状态下，有两个差异实验结果，一项研究提出了一个旋转玻璃状态，而另一个研究将材料作为Ferromagnet引入。在这项研究中，我们试图通过使用密度功能理论和蒙特卡洛模拟来解决此问题。我们通过在Ab Initio GGA+$ U $计算中改变Hubbard $ u $参数来得出不同的自旋模型。对于最多的Hubbard $ U $，我们可以获得旋转汉密尔顿的主要术语是双季度和最近的邻居海森伯格交流互动。通过将这些模型的蒙特卡洛模拟与实验进行比较，我们发现y $ _ {2} $ mn $ _ {2} $ o $ $ $ _ {7} $的铁磁基态是与实验最兼容的。我们还将y $ _ {2} $ mo $ $ $ _ {2} $ o $ $ _ {7} $作为具有旋转玻璃行为的无缺陷的Pyrochlore系统的原型，并将其与y $ $ _ {2} $ _ {2} $ Mn $ _ {2} $ _ {2} $ o $ $ _ $ _ {7} $进行比较。轨道自由度被认为是将无缺陷的pyrochlore转换为y $ _ {2} $ mn $ _ {2} $ o $ $ $ _ {7} $的主要因素。通过更改Mo Atoms的$ D $轨道职业，我们的GGA+$ U $ $ $ _ {2} $ mo $ $ $ $ $ $ _ {2} $ o $ $ _ {7} $表示许多几乎变性的状态，具有不同的$ d $ orbital方向，这表明了$ d $ d $ d $ d $ d $ d $ d $ Orbital efrees of turn材料的易于。而对于y $ _ {2} $ mn $ _ {2} $ o $ _ {7} $，我们找到具有固定轨道定向的单个基态。因此，我们所有的从头算法确认y $ _ {2} $ Mn $ _ {2} $ o $ $ $ _ {7} $作为铁磁系统。
There are two discrepant experimental results on the magnetic ground state of Y$_{2}$Mn$_{2}$O$_{7}$, one study proposes a spin glass state, while another introduces the material as a ferromagnet. In this study, we attempt to resolve this issue by employing density functional theory and Monte Carlo simulations. We derive different spin models by varying the Hubbard $U$ parameter in ab initio GGA+$U$ calculations. For the most range of Hubbard $U$, We obtain that the leading terms in the spin Hamiltonian are bi-quadratic and the nearest neighbor Heisenberg exchange interactions. By comparing Monte Carlo simulations of these models with the experiments, we find a ferromagnetic ground state for Y$_{2}$Mn$_{2}$O$_{7}$ as the most compatible with experiments. We also consider Y$_{2}$Mo$_{2}$O$_{7}$ as a prototype of the defect-free pyrochlore system with spin-glass behavior and compare it with Y$_{2}$Mn$_{2}$O$_{7}$. The orbital degrees of freedom are considered as a leading factor in converting a defect-free pyrochlore such as Y$_{2}$Mn$_{2}$O$_{7}$ to a spin glass system. By changing the $d$ orbital occupations of Mo atoms, our GGA+$U$ calculations for Y$_{2}$Mo$_{2}$O$_{7}$ indicate many nearly degenerate states with different $d$ orbital orientations which reveals $d$ orbital degrees of freedom in this material. While for Y$_{2}$Mn$_{2}$O$_{7}$, we find a single ground state with a fixed orbital orientation. Consequently, all of our ab initio approaches confirm Y$_{2}$Mn$_{2}$O$_{7}$ as a ferromagnetic system.
