二维范德华材料中铁磁性的出现引起了人们的广泛兴趣。然而，铁磁不稳定性一直是一个问题。在这项工作中，通过使用第一性原理计算，我们确定的临界范围内的应变和掺杂的双层Cr 2 Ge 2 Te 6的铁磁稳定性可以提高。在临界范围外，拉伸应变可引起铁磁到反铁磁的相变，而压应变的增加或静电掺杂可使易磁化轴方向由面外转变为面内。我们还预测了一个电子掺杂范围，在此范围内，铁磁性可以得到增强，同时保持铁磁性稳定。此外，我们发现，压缩应变可以逆转的自旋极化的电子在导带的最低点，使两类半金属可以诱导通过控制静电掺杂的双层Cr2Ge2Te6。这些结果将有助于实现低维材料的铁磁稳定性。
英文摘要：
The emergence of ferromagnetism in two-dimensional van der Waals materials has aroused broad interest. However, the ferromagnetic instability has been a problem remained. In this work, by using the first-principles calculations, we identified the critical ranges of strain and doping for the bilayer Cr2Ge2Te6 within which the ferromagnetic stability can be enhanced. Beyond the critical range, the tensile strain can induce the phase transition from the ferromagnetic to the antiferromagnetic, and the direction of magnetic easy axis can be converted from out-of-plane to in-plane due to the increase of compressive strain, or electrostatic doping. We also predicted an electron doping range, within which the ferromagnetism can be enhanced, while the ferromagnetic stability was maintained. Moreover, we found that the compressive strain can reverse the spin polarization of electrons at the conduction band minimum, so that two categories of half-metal can be induced by controlling electrostatic doping in the bilayer Cr2Ge2Te6. These results should shed a light on achieving ferromagnetic stability for low-dimensional materials.
We theoretically propose a new stabilization mechanism of a skyrmion crystal (SkX) in a bilayer triangular lattice system consisting of the ferromagnetic and the antiferromagnetic layers. By performing variational calculations and Monte Carlo simulations in a complementary way, we find that a magnetic frustration between the ferromagnetic and antiferromagnetic layers is a source of a finite-Q spiral state and the SkX in the strong interlayer coupling regime. We also show that the degree of frustration is related to the interlayer exchange interaction. The stronger interlayer coupling tends to …
Investigation of ferromagnetic domain behavior and phase transition at nanoscale in bilayer manganites
理解锰氧化物中巨磁电阻的基本机制和现象学主要集中在原子和纳米级物理学上，如双交换，相分离和电荷顺序。在这里，我们认为一个更宏观的观点的锰氧化物材料的物理，报告的铁磁畴行为在一个双层锰氧化物样品的名义组成的La $_{2-2x}$ Sr $_{1+2x}$ Mn $_2$ O $_7$与$x=0.38$，研究使用原位洛伦兹透射电子显微镜。阐明了磁晶各向异性对畴壁结构的作用。在冷却时，在$a-b$平面内的居里温度下，可以看到磁畴对比度首先出现。随着温度的进一步降低，磁畴面积分数的变化被用来估计描述铁磁相变的临界指数。铁磁相变伴随着一个独特的纳米级颗粒对比接近居里温度，我们推断这是与铁磁纳米团簇的存在下，在一个顺磁性的矩阵，这还没有在双层锰氧化物的报道。
Flat bands in twisted moire superlattices support a variety of topological and strongly correlated phenomena along with easily tunable electrical and optical properties. Here, we demonstrate the existence of tunable, long-lived, and flat intraband and interband terahertz plasmons in twisted double bilayer graphene. We show that the interband plasmons originate from the presence of a Van Hove singularity in the joint density of states and a finite Berry connection between the pair of bands involved. We find that the gapped interband plasmon mode has a universal dispersion, and the plasmon gap i…
Spin angular momentum transfer in magnetic bilayers offers the possibility of ultrafast and low-loss operation for next-generation spintronic devices. We report the field- and temperature- dependent measurements on the magnetization precessions in Co$_2$FeAl/(Ga,Mn)As by time-resolved magneto-optical Kerr effect (TRMOKE). Analysis of the effective Gilbert damping and phase shift indicates a clear signature of an enhanced dynamic exchange coupling between the two ferromagnetic (FM) layers due to the reinforced spin pumping at resonance. The temperature dependence of the dynamic exchange-couplin…
