Two-dimensional
(2D) magnetic materials have attracted much attention
due to their unique magnetic properties and promising applications
in spintronics. Here, we report on the growth of ferrous chloride
(FeCl2) films on Au(111) and graphite with atomic thickness
by molecular-beam epitaxy (MBE) and the layer-dependent magnetic properties
by density functional theory (DFT) calculations. The growth follows
a layer-by-layer mode with adjustable thickness from sub-monolayer
to a few layers. Four types of moiré superstructures of a single-layer
FeCl2 on graphite and two types of atomic vacancies on
Au(111) have been identified based on high-resolution scanning tunneling
microscopy (STM). It turned out that the single- and few-layer FeCl2 films grown on Au(111) exhibit a 1T structure. The DFT calculations
reveal that a single-layer 1T-FeCl2 has a ferromagnetic
ground state. The minimum-energy configuration of a bilayer FeCl2 is satisfied for the 1T–1T structure with ferromagnetic
layers coupled antiferromagnetically. These results make FeCl2 a promising candidate as ideal electrodes for spintronic
devices providing large magnetoresistance.
In the framework of the Eliashberg formalism the free energy difference between the superconducting and normal state for the molecular metallic hydrogen was calculated. The pressure values p1 = 347 GPa and p2 = 428 GPa were taken into consideration. It has been shown, that together with the increase of the pressure, grows the value of the specific heat jump at the critical temperature and the value of the thermodynamic critical field near zero Kelvin: [∆C (TC)] p2 / [∆C (TC )] p1 ≃ 2.33 and [HC (0)] p2 / [HC (0)] p1 ≃ 1.74. Next, it has been stated, that the ratio ∆C (TC ) /C N (TC ) also increases from 1.91 to 2.39; whereas TCC N (TC) /H 2 C (0) decreases from 0.152 to 0.140. The last results prove that the considered parameters significantly diverge from the prediction based on the BCS model.
We study the stability of the hydrogen molecule interacting with the environment according to the balanced gain and loss energy scheme. We determined the properties of the molecule taking into account all electronic interactions, where the parameters of the Hamiltonian have been computed by using the variational method. The interaction of the hydrogen molecule with the environment was modeled parametrically (γ) with the help of the non-hermitian operator. We have shown that the hydrogen molecule is dynamically unstable. The dissociation time (TD) decreases, if the γ parameter increases (for γ → 0, we get TD → +∞). At the dynamic instability of the hydrogen molecule overlaps its static instability as the coupling constant γ increases. We observed the decrease in the dissociation energy and the existence of the metastable state of the molecule (γMS = 0.659374 Ry). The hydrogen molecule is statically unstable for γ > γD = 1.024638 Ry. One can also observed the PT symmetry breaking effect for the electronic Hamiltonian (γPT = 0.520873 Ry). However, it does not affect the properties of the hydrogen molecule, such as: the electronic Hamiltonian parameters, the phonon and rotational energy, and the values of the electron-phonon coupling constants.
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