Combining theory with experiments, we study the phase stability, elastic properties, electronic structure and hardness of layered ternary borides AlCr 2 B 2 , AlMn 2 B 2 , AlFe 2 B 2 , AlCo 2 B 2 , and AlNi 2 B 2 . We find that the first three borides of this series are stable phases, while AlCo 2 B 2 and AlNi 2 B 2 are metastable. We show that the elasticity increases in the boride series, and predict that AlCr 2 B 2 , AlMn 2 B 2 , and AlFe 2 B 2 are more brittle, while AlCo 2 B 2 and AlNi 2 B 2 are more ductile. We propose that the elasticity of AlFe 2 B 2 can be improved by alloying it with cobalt or nickel, or a combination of them.We present evidence that these ternary borides represent nanolaminated systems. Based on SEM measurements, we demonstrate that they exhibit the delamination phenomena, which leads to a reduced hardness compared to transition metal mono-and diborides. We discuss the background of delamination by analyzing chemical bonding and theoretical work of separation in these borides.

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In recent years there has been an intense interest in understanding the microscopic mechanism of thermally induced magnetization switching driven by a femtosecond laser pulse. Most of the effort has been dedicated to periodic crystalline structures while the amorphous counterparts have been less studied. By using a multiscale approach, i.e., first-principles density functional theory combined with atomistic spin dynamics, we report here on the very intricate structural and magnetic nature of amorphous Gd-Fe alloys for a wide range of Gd and Fe atomic concentrations at the nanoscale level. Both structural and dynamical properties of Gd-Fe alloys reported in this work are in good agreement with previous experiments. We calculated the dynamic behavior of homogeneous and inhomogeneous amorphous Gd-Fe alloys and their response under the influence of a femtosecond laser pulse. In the homogeneous sample, the Fe sublattice switches its magnetization before the Gd one. However, the temporal sequence of the switching of the two sublattices is reversed in the inhomogeneous sample. We propose a possible explanation based on a mechanism driven by a combination of the Dzyaloshinskii-Moriya interaction and exchange frustration, modeled by an antiferromagnetic second-neighbor exchange interaction between Gd atoms in the Gd-rich region. We also report on the influence of laser fluence and damping effects in the all-thermal switching.

By means of theoretical modeling and experimental synthesis and characterization, we investigate the structural properties of amorphous Zr-Si-C. Two chemical compositions are selected, Zr 0.31 Si 0.29 C 0.40 and Zr 0.60 Si 0.33 C 0.07 . The amorphous structures are generated in the theoretical part of our work, by the stochastic quenching (SQ) method, and detailed comparison is made as regards structure and density of the experimentally synthesized films. These films are analyzed experimentally using Xray absorption spectroscopy, transmission electron microscopy and X-ray diffraction.Our results demonstrate for the first time a remarkable agreement between theory and experiment concerning bond distances and atomic coordination of this complex amorphous metal carbide. The demonstrated power of the SQ method opens up avenues for theoretical predictions of amorphous materials in general.

Amorphous W-S-N in the form of thin films has been identified experimentally as an ultra-low friction material, enabling easy sliding by the formation of a WS 2 tribofilm. However, the atomic-level structure and bonding arrangements in amorphous W-S-N, which give such optimum conditions for WS 2 formation and ultra-low friction, are not known. In this study, amorphous thin films with up to 37 at.% N are deposited, and experimental as well as state-of-the-art ab initio techniques are employed to reveal the complex structure of W-S-N at the atomic level. Excellent agreement between experimental and calculated coordination numbers and bond distances is demonstrated. Furthermore, the simulated structures are found to contain N bonded in molecular form, i.e. N 2 , which is experimentally confirmed by near edge X-ray absorption fine structure and X-ray photoelectron spectroscopy analysis. Such N 2 units are located in cages in the material, where they are coordinated mainly by S atoms. Thus this ultra-low friction material is shown to be a complex amorphous network of W, S and N atoms, with easy access to W and S for continuous formation of WS 2 in the contact region, and with the possibility of swift removal of excess nitrogen present as N 2 molecules.

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We investigated surface properties of metals by performing firstprinciples calculations. A systematic database was established for the surface relaxation, surface energy (), and surface stress () for metallic elements in the periodic table. The surfaces were modeled by multilayered slab structures along the direction of lowindex surfaces. The surface energy of simple metals decreases as the atomic number increases in a given group, while the surface stress has its minimum in the middle. The transition metal series show parabolic trends for both and with a dip in the middle. The dip occurs at half band filling due to a longrange Friedel oscillation of the surface charge density, which induces a strong stability to the Peirelslike transition. In addition, due to magnetic effects, the dips in the 3d metal series are shallower and deeper for and , respectively, than those of the 4d and 5d metals. The surface stress of the transition metals is typically positive, only Cr and Mn have a negative for the (100) surface facet, indicating that they are under compression. The light actinides have an increasing trend according to the atomic number. The present work provides a useful and consistent database for the theoretical modelling of surface phenomena.

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