An effective spin model on the honeycomb lattice for the description of magnetic properties in two-dimensional Fe3_3GeTe2_2

Fe$_3$GeTe$_2$ attracts significant attention due to technological perspectives of realizing room temperature ferromagnetism in two-dimensional materials. Here we show that due to structural peculiarities of the Fe$_3$GeTe$_2$ monolayer, short distance between the neighboring iron atoms induces a strong exchange coupling. This strong coupling allows us to consider them as an effective cluster with a magnetic moment $\sim$5 $\mu_B$, giving rise to a simplified spin model on a bipartite honeycomb lattice with the reduced number of long-range interactions. The simplified model perfectly reproduces the results of the conventional spin model, but allows for a more tractable description of the magnetic properties of Fe$_3$GeTe$_2$, which is important, e.g., for large-scale simulations. Also, we discuss the role of biaxial strain in the stabilization of ferromagnetic ordering in Fe$_3$GeTe$_2$.Comment: 7 pages, 7 figure

Electron transport and scattering mechanisms in ferromagnetic monolayer Fe3GeTe2

Abstract We study intrinsic charge-carrier scattering mechanisms and determine their contribution to the transport properties of the two-dimensional ferromagnet Fe3GeTe2. We use state-of-the-art first-principles calculations combined with the model approaches to elucidate the role of the electron-phonon and electron-magnon interactions in the electronic transport. Our findings show that the charge carrier scattering in Fe3GeTe2 is dominated by the electron-phonon interaction, while the role of magnetic excitations is marginal. At the same time, the magnetic ordering is shown to effect essentially on the electron-phonon coupling and its temperature dependence. This leads to a sublinear temperature dependence of the electrical resistivity near the Curie temperature, which is in line with experimental observations. The room temperature resistivity is estimated to be ~ 35 μΩ ⋅ cm which may be considered as a lower intrinsic limit for monolayer Fe3GeTe2

Manipulation of femtosecond laser filamentation by wire mesh amplitude mask

The results of numerical simulation on the propagation of high-power femtosecond laser pulses in air under conditions of the amplitude modulation are presented. Laser pulse amplitude modulation is realized by using the metal mesh-masks, which divide the initial laser beam into lower-energy parts (subbeams). We show that, in general, the beam energy partitioning by metal meshes reduces the total length of beam filamentation region in air, whereas the longitudinal continuity of the laser plasma distribution in the filaments is considerably improved. A strong dependence of the filamentation region parameters (starting coordinate, length, longitudinal continuity) on the position of the mesh-mask relative to the laser beam axis is also revealed. It turns out that under certain conditions, when the beam axis points to the mesh crossing, the spatial position of the filaments can be shifted further along the propagation path by increasing the size of the mesh cells. Alternatively, if the beam center exposes the mesh cell opening, the filamentation start coordinate decreases monotonically when the mesh becomes sparser. Additionally, the parameters of the filamentation region exhibit high sensitivity to the mesh wire thickness that can dominate the influence of mesh position and cell size

A Complex of Marine Geophysical Methods for Studying Gas Emission Process on the Arctic Shelf

The Russian sector of the arctic shelf is the longest in the world. Quite a lot of places of massive discharge of bubble methane from the seabed into the water column and further into the atmosphere were found there. This natural phenomenon requires an extensive complex of geological, biological, geophysical, and chemical studies. This article is devoted to aspects of the use of a complex of marine geophysical equipment applied in the Russian sector of the arctic shelf for the detection and study of areas of the water and sedimentary strata with increased saturation with natural gases, as well as a description of some of the results obtained. This complex contains a single-beam scientific high-frequency echo sounder and multibeam system, a sub-bottom profiler, ocean-bottom seismographs, and equipment for continuous seismoacoustic profiling and electrical exploration. The experience of using the above equipment and the examples of the results obtained in the Laptev Sea have shown that these marine geophysical methods are effective and of particular importance for solving most problems related to the detection, mapping, quantification, and monitoring of underwater gas release from the bottom sediments of the shelf zone of the arctic seas, as well as the study of upper and deeper geological roots of gas emission and their relationship with tectonic processes. Geophysical surveys have a significant performance advantage compared to any contact methods. The large-scale application of a wide range of marine geophysical methods is essential for a comprehensive study of the geohazards of vast shelf zones, which have significant potential for economic use