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Here, we present results of a computational study of electronic, magnetic, and structural properties of FeVTaAl and FeCrZrAl, quaternary Heusler alloys that have been recently reported to exhibit spin-gapless semiconducting behavior. Our calculations indicate that these materials may crystallize in regular Heusler cubic structure, which has a significantly lower energy than the inverted Heusler cubic phase. Both FeVTaAl and FeCrZrAl exhibit ferromagnetic alignment, with an integer magnetic moment per unit cell at equilibrium lattice constant. Band structure analysis reveals that while both FeVTaAl and FeCrZrAl indeed exhibit nearly spin-gapless semiconducting electronic structure at their optimal lattice parameters, FeVTaAl is a 100% spin-polarized semimetal, while FeCrZrAl is a magnetic semiconductor. Our calculations indicate that expansion of the unit cell volume retains 100% spin-polarization of both compounds. In particular, both FeVTaAl and FeCrZrAl are 100% spin-polarized magnetic semiconductors at the largest considered lattice constant. At the same time, at smaller lattice parameters, both compounds exhibit a more complex electronic structure, somewhat resembling half-metallic properties. Thus, both of these alloys may be potentially useful for practical applications in spin-based electronics, but their electronic structure is very sensitive to the external pressure. We hope that these results will stimulate experimental efforts to synthesize these materials. 

Here, we present results of combined experimental and computations study of V2CoAl, a Heusler alloy that exhibits nearly perfect spin-polarization. Our calculations indicate that this material maintains a high degree of spin-polarization (over 90%) in the wide range of lattice parameters, except at the largest considered unit cell volume. The magnetic alignment of V2CoAl is ferrimagnetic, due to the antialignment of the magnetic moments of vanadium atoms in their two sublattices. The calculated total magnetic moment per formula unit is nearly integer at the optimal lattice parameter and at the smaller volumes of the unit cell, but it deviated from the integer values as the unit cell expands. This is consistent with the calculated variation in the degree of spin polarization with lattice constant. The expected ferrimagnetic behavior has been observed in the arc-melted V2CoAl sample, with a Curie temperature of about 80 K. However, the saturation magnetization is significantly smaller than the theoretical prediction of ∼2 μB/f.u., most likely due to the observed B2-type atomic disorder. The samples exhibit metallic electron transport across the measurement range of 2 K to 300 K. 

Abstract Here, we present results of a computational and experimental study of adsorption of various metals on MoS₂. In particular, we analyzed the binding mechanism of four metallic elements (Ag, Au, Cu, Ni) on MoS₂. Among these elements, Ni exhibits the strongest binding and lowest mobility on the surface of MoS₂. On the other hand, Au and Ag bond very weakly to the surface and have very high mobilities. Our calculations for Cu show that its bonding and surface mobility are between these two groups. Experimentally, Ni films exhibit a composition characterized by randomly oriented nanoscale clusters. This is consistent with the larger cohesive energy of Ni atoms as compared with their binding energy with MoS₂, which is expected to result in 3D clusters. In contrast, Au and Ag tend to form atomically flat plateaued structures on MoS₂, which is contrary to their larger cohesive energy as compared to their weak binding with MoS₂. Cu displays a surface morphology somewhat similar to Ni, featuring larger nanoscale clusters. However, unlike Ni, in many cases Cu exhibits small plateaued surfaces on these clusters. This suggests that Cu likely has two competing mechanisms that cause it to span the behaviors seen in the Ni and Au/Ag film morphologies. These results indicate that calculations of the initial binding conditions could be useful for predicting film morphologies. In addition, out calculations show that the adsorption of adatoms with odd electron number like Ag, Au, and Cu results in 100% spin-polarization and integer magnetic moment of the system. Adsorption of Ni adatoms, with even electron number, does not induce a magnetic transition.