42 research outputs found
Theoretical study of the intrinsic magnetic properties of disordered alloys: a mean-field approach
The magnetic properties of the alloy system for 0 x
0.10 are studied by using a mean-field approximation based on the
Bogoliubov inequality. Ferromagnetic Fe-Fe spin correlations and
antiferromagnetic Fe-Ru and Ru-Ru exchanges have been considered to describe
the temperature dependence of the Curie temperature and low temperature
magnetization. A composition dependence has been imposed in the exchange
couplings, as indicated by experiments. From a least-square fitting procedure
to the experimental results an estimation of the interaction parameters was
obtained, which yielded the low temperature dependence of the magnetization and
of the ferromagnetic Curie temperature. A good agreement was obtained with
available experimental results.Comment: Two figures, to appear in J. Phys. Cond. Matte
Electronic structure of A15-type compounds: V 3Co, V 3Rh,V 3Ir and V 3Os
71.15.Ap Basis sets, 71.20.Lp Intermetallic compounds, 74.25.Jb Electronic structure, 74.70.Ad Metals; alloys and binary compounds,
Electronic structure and magnetization of FeâCo alloys and multilayers
The magnetic properties and electronic structure of bcc FeâCo alloys and multilayers are investigated with the first-principles molecular cluster discrete variational method. The density of states and the contact interactions are obtained for the central atom of each cluster. Besides the local magnetic moment and the isomer shift the occupancies of 3d, 4s, and 4p shells are investigated when Co atoms are introduced in the immediate vicinity of iron sites. The calculations indicate a varying magnetic moment for Fe atoms and a constant value for Co atoms which is in agreement with experiments. For the superstructures, our results indicate a strong dependence of the local moment, contact field, and isomer shift for Fe atoms with the thick of iron layers. The internal field increases for thicker Fe layers while the local moment decreases which is also in accordance with experimental predictions
Martensitic phase transition from cubic to tetragonal V
In this study we focus on the subtle changes which occur in the
electronic structure and in the Fermi surface topology with the
low temperature (21.3Â K) cubic â tetragonal martensitic
phase transition in V3Si. From the calculations it has been
verified the occurrence of a charge transfer from V atoms to Si
atoms, with the phase transition to a tetragonal variant of the
A-15 structure. The orbital population of s- and p-states of V
atoms in the 2e and 4k sites of the tetragonal phase are
practically the same. Major differences are seen in the occupation
of d-states. There is a decrease in the average electronic energy
with the structural transition, which occurs as a result of the
emptying of V d-states (mostly from bands 19â20), and these
electrons enter preferentially into the Si p-orbitals. The present
results thus indicate that the electronic features of the
martensitic transition of V3Si, besides being intimately related to
the splitting of the Î12 into the Î1+ and
Î3+ states and the position of the Î1+ state
relatively to EF, is mainly associated with the gain in the
average electronic energy which occurs from an electron transfer
from V-d â Si-p states. This is the main source to
explain the stability of the tetragonal phase formed at low
temperature in this system
Density functional theory study of Fe(3)Ga
First-principles scalar relativistic calculations in supercells of 16 atoms are used to represent disordered B2 ordering of Fe(3)Ga in order to observe the effect of Ga-Ga pairs on the electronic structure of this alloy. From a comparison with pure bcc Fe it is observed that the energy position and occupation of e(g) and t(2g) states are largely affected by the Ga-Ga pairs and strengthened intraplane interactions takes place. The results show that a larger hybridization of the conduction band is in the source of the magnetostriction enhancement experimentally observed in Galfenol. (C) 2011 American Institute of Physics. [doi:10.1063/1.3525609