Interplay between structure and magnetism in hydride iron-vanadium systems

Abstract

The structural and electronic properties of dimers, bulk, and alloys of Fe and V upon loading with hydrogen have been investigated using the density-functional method Spanish Initiative for Electronic Simulation of Thousand of Atoms. We have calculated the hydrogen-induced modifications of both the geometrical structure and the magnetic properties, which have been found to be closely related to each other. The general trends derived from our results are in good agreement with those found in the experimental characterizations of hydrogen-loaded Fe/V multilayer systems. In particular, we have found that hydrogen prefers a V environment when inserted in the alloy systems at high concentration; it occupies octahedral positions leading to a strong anisotropic expansion of the lattice accompanied by an increase in the local Fe magnetic moments. We have found that the main trends obtained in the extended systems were already present in the most stable geometrical and spin isomers of the freestanding FeVH clusters.

Ab initiostudy of hydrogen insertion in ultrathin transition metal doped V films: Structural and electronic properties

“…Among the internal ones, the most favorable site for H insertion is the tetrahedral position T2, for which we obtain the smallest structural reconstruction. Both internal T2 and surface HOLLOW sites present a bonding of H with a pair of vanadium atoms that is reminiscent of the stable configuration of the V+V+H trimer, found in our previous work, 19 in which H forms an isosceles triangle with the V-V dimer and sits on the summit of the triangle. The results for T2 site are in agreement with bulk data for vanadium bcc.…”

“…The results for T2 site are in agreement with bulk data for vanadium bcc. 19 Inserting H in the octahedral sites produce larger structural distortions, as illustrated by the variation in ⌬a and ⌬b ͑Fig. 1͒.…”

“…30 In the case of V atoms, this has been shown on the one hand to considerably improve the description of the magnetic trends in semi-infinite systems 31,32 and on the other hand it improves the interatomic distance of the dimer. 19 We also note that the electronic configuration used to generate the Fe pseudopotential corresponds to an excited state ͑see Table II͒ because this pseudopotential is known to re- produce the correct spin state of Fe dimers. 33 We have tested that these pseudopotentials accurately reproduced the eigenvalues of different excited states of the respective isolated atoms.…”

“…We also smoothed the Fermi distribution function that enters in the calculation of the density matrix with an electronic temperature of 300 K. The same theoretical approach was used in our recent study of free-standing Fe-V-H trimers and B2 FeV alloys. 19 A ͑001͒ bcc ultrathin film of three vanadium monolayers, called TL ‫ء‬V , has been modeled using a supercell with 48 nonequivalent atoms ͑49 when the H atom is inserted͒ and periodic boundary conditions, inserting enough vacuum space along the ͑001͒ direction to avoid interaction between the surfaces of neighboring cells. The estimation of the required vacuum space to separate the surfaces of the V films of neighboring cells Ϸ15 Å is done in terms of the length of the basis functions which are strictly localized in SIESTA.…”

“…19 In the present work we complement this investigation by conducting calculations in the ultrathin film regime and we further study the effect of doping with a variety of substitutional atomic impurities which may affect the H storage properties and the electronic properties. For this purpose, we have built up a system composed of three monolayers of vanadium in which a transition metal doping atom replaces a V one at the central layer.…”