五角结构单层铁磁压电CoAsS
Single-Layer Ferromagnetic and Piezoelectric CoAsS with Pentagonal Structure
摘要：
单层五边形材料是一种新兴的二维（2D）材料家族，由于构建块是五边形而不是许多2D材料中的六边形，因此可以表现出新颖的特性。基于我们最近预测的单层五边形反铁磁半导体CoS $_2$，我们用As原子取代了单胞中的两个S原子，形成了单层五边形CoAsS。根据声子计算，所得单层材料是动态稳定的。我们发现两个剧烈的变化，单层五边形CoAsS的性质相比，那些CoS $_2$。首先，我们发现从AFM到FM有序的磁性转变。我们认为这是由于As原子的电负性较低，导致Co离子间超交换作用的桥连作用减弱所致。单层五边形CoAsS也显示出显着更强的磁晶各向异性能，由于更强的自旋轨道耦合。我们还用蒙特卡罗模拟计算了单层五边形CoAsS的居里温度，预测的居里温度为103 K。其次，我们发现，单层五边形CoAsS具有压电性，这是缺乏在单层五边形CoS $_2$由于其对称中心。计算的压电系数也是相当大的。FM有序和压电特性的罕见共存使得单层五边形CoAsS成为一种有前途的多功能二维材料。
英文摘要：
Single-layer pentagonal materials are an emerging family of two-dimensional (2D) materials that could exhibit novel properties due to the building blocks being pentagons instead of hexagons as in numerous 2D materials. Based on our recently predicted single-layer pentagonal CoS$_2$ that is an antiferromagnetic (AFM) semiconductor, we replace two S atoms by As atoms in a unit cell to form single-layer pentagonal CoAsS. The resulting single-layer material is dynamically stable ac-cording to the phonon calculations. We find two drastic changes in the properties of single-layer pentagonal CoAsS in comparison with those of CoS$_2$. First, we find a magnetic transition from the AFM to FM ordering. We understand that the transition is caused by the lower electronegativity of As atoms, leading to the weakened bridging roles on the superexchange interactions be-tween Co ions. Single-layer pentagonal CoAsS also shows significantly stronger magnetocrystalline anisotropy energy due to stronger spin-orbit coupling. We additionally perform Monte Carlo simulations to calculate the Curie temperature of single-layer pentagonal CoAsS and the predicted Curie temperature is 103 K. Second, we find that single-layer pentagonal CoAsS exhibits piezoelectricity, which is absent in single-layer pentagonal CoS$_2$ due to its center of symmetry. The computed piezoelectric coefficients are also sizable. The rare coexistence of FM ordering and piezoelectric properties makes single-layer pentagonal CoAsS a promising multifunctional 2D material.
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