论文标题
表征和克服磁电抗铁磁体中的表面顺磁性
Characterizing and Overcoming Surface Paramagnetism in Magnetoelectric Antiferromagnets
论文作者
论文摘要
我们使用密度功能理论和蒙特卡洛计算的组合来计算有限温度下的磁电$ \ mathrm {Cr_2o_3} $中的表面磁化。这种抗铁磁体缺乏反转和时反转对称性，是由对称性要求在特定表面终止上具有未补偿的磁化密度的。在这里，我们首先表明$（001）$表面上的磁矩最上层在大容量的néel温度下保持顺磁性，从而使表面磁化密度的理论估计与实验一致。我们证明，与散装相比，较低的表面排序温度是终止降低有效的海森堡耦合时表面磁化的一般特征。然后，我们提出了两种方法，可以在$ \ mathrm {Cr_2o_3} $中的表面磁化在较高的温度下稳定。具体而言，我们表明，表面磁离子的有效耦合可以通过不同的表面米勒平面选择或$ \ mathrm {fe} $掺杂大大增加。我们的发现提供了对AFMS表面磁化特性的改进理解。
We use a combination of density functional theory and Monte Carlo calculations to calculate the surface magnetization in magnetoelectric $\mathrm{Cr_2O_3}$ at finite temperatures. Such antiferromagnets, lacking both inversion and time-reversal symmetries, are required by symmetry to posses an uncompensated magnetization density on particular surface terminations. Here, we first show that the uppermost layer of magnetic moments on the $(001)$ surface remain paramagnetic at the bulk Néel temperature, bringing the theoretical estimate of surface magnetization density in line with experiment. We demonstrate that the lower surface ordering temperature compared to bulk is a generic feature of surface magnetization when the termination reduces the effective Heisenberg coupling. We then propose two methods by which the surface magnetization in $\mathrm{Cr_2O_3}$ could be stabilised at higher temperatures. Specifically, we show that the effective coupling of surface magnetic ions can be drastically increased either by a different choice of surface Miller plane, or by $\mathrm{Fe}$ doping. Our findings provide an improved understanding of surface magnetization properties in AFMs.
