Magnetic and structural properties ofIIA−Vnitrides

physica status solidi (c), 2005

A systematic computational study of the relative stability of the zinblende (ZB) versus rocksalt (NaCl or RS) structure of the transition metal nitrides (TMN) is presented. The early TMN prefer NaCl, the later ones ZB with the crossing occuring at MnN. The minimum energy lattice constant of the ZB phase is always significantly larger than that of RS. The TMN are shown to have a stronger tendency to be magnetic in the RS than in the ZB phase.

Journal of Magnetism and Magnetic Materials, 2015

Based on first principles spin-polarized density functional theory, the structural, elastic electronic and magnetic properties of Zn 1 À x V x Se (for x ¼0.25, 0.50, 0.75) in zinc blende structure have been studied. The investigation was done using the full-potential augmented plane wave method as implemented in WIEN2k code. The exchange-correlation potential was treated with the generalized gradient approximation PBE-GGA for the structural and elastic properties. Moreover, the PBE-GGAþU approximation (where U is the Hubbard correlation terms) is employed to treat the "d" electrons properly. A comparative study between the band structures, electronic structures, total and partial densities of states and local moments calculated within both GGA and GGAþU schemes is presented. The analysis of spin-polarized band structure and density of states shows the half-metallic ferromagnetic character and are also used to determine s(p)-d exchange constants N 0 α (conduction band ) and N 0 β (valence band) due to Se(4p)-V(3d) hybridization. It has been clearly evidence that the magnetic moment of V is reduced from its free space change value of 3 m B and the minor atomic magnetic moment on Zn and Se are generated.

The European Physical Journal B - Condensed Matter, 2003

We report on the crystallographic and magnetic structure of the geometrically frustrated spinel ZnV2O4 as determined by neutron powder diffraction. At T = 51 K, a cubic-to-tetragonal phase transition takes place. The low temperature crystallographic structure is characterized by the space group I41/amd and unit cell dimensions a/ √ 2 × a/ √ 2 × a with a being the lattice constant of the cubic phase. The corresponding antiferromagnetic structure of the vanadium sublattice can be described by a propagation vector k = (001) with the magnetic moments being aligned parallel to the c-axis. The ordered magnetic moment is 0.65(5) µB per V 3+ ion. The experimental results are in accord with recent theoretical models proposing spin-driven Jahn-Teller distortions. The results are also compared with reports on non-ordering ZnV2O4.

In this study, we examine the structural, electronic, magnetic and bonding properties of zincblende phase Zn1-xVxTe (x = 0.0625, 0.125, 0.25) compounds to present them as suitable candidates for spintronic applications. Density functional theory calculations have been used by implementing the accurate full-potential linear-augmented-planewave plus local-orbital method. Structural properties have been computed using Wu–Cohen generalized gradient approximation, whereas the modified Becke and Johnson local (spin) density approximation (mBJLDA) function has been employed for the evaluating ground state electronic properties and ferromagnetic behavior. The half-metallic (HM) ferromagnetism in Zn1-xVxTe is analyzed in terms of V-3d states and it is shown that mBJLDA predicts wide HM gaps which promise the possibility of achieving V-doped ZnTe with high Curie temperature. The spin exchange splittings Δx(d) and Δx(pd) have been estimated and the contribution of conduction band (CB) and valence band (VB) in exchange splitting is calculated in terms of the exchange constants N0α and N0β. Furthermore, spin-polarized charge density calculation is presented for elucidating the bonding nature, while pressure dependence of total magnetic moment for three concentrations of V-doped ZnTe is also discussed.

Physical Review B, 2006

On the basis of ab initio calculations employing density functional theory ͑DFT͒ we investigate half metallic ferromagnetism in zinc-blende and wurtzite compounds composed of group I/II metals as cations and group V elements as anions. We find that the formation of ferromagentic order requires large cell volumes, high ionicity and a slight hybridization of anion p and cation d states around the Fermi energy. Our calculations show that a ferromagnetic alignment of the spins is energetically always more stable than simple AF arrangements, which makes these materials possible candidates for spin injection in spintronic devices. To clarify the conditions for the flat p-band carrying the magnetism, we present results of a tight binding analysis.

ChemInform, 2007

Dedicated to Dr. Bernard Chevalier on the occasion of his 60 th birthday Magnetic properties and bonding analyses of perovskite structure-derived TFe 3 N (T = Ru, Os) nitrides have been investigated within density functional theory using both pseudo potential and all electron methods. At equilibrium, spin degenerate non-magnetic (NM) and ferromagnetic (FM) calculations of energy versus volume show that the ground state of the two compounds is ferromagnetic. Magnetic moments of Ru/Os and Fe, respectively, being situated at two different crystallographic sites are studied over a wide range of the cubic lattice parameter. The volume expansion indicates that iron atoms show itinerant magnetism while Ru and Os exhibit a localized behavior. Important magnetovolume effects are observed, with saturation of the magnetic moment reached in RuFe 3 N but not in OsFe 3 N. The electronic structure is visualized for the different binding characters Fe-N versus Ru/Os-N with the help of electron localization plots. The density of states of the ferromagnetic ground state is interpreted on the basis of a covalent magnetic model which goes beyond the Stoner rigid band model. An Invar-like behavior is predicted for the two nitrides.

Journal of Alloys and Compounds, 2010

We report a first-principles study of structural, electronic and magnetic properties of crystalline alloys Zn 1−x TM x S (TM = Fe, Co and Ni) at x = 0.25. Structural properties are computed from the total ground state energy convergence and it is found that the cohesive energies of Zn 1−x TM x S are greater than that of zincblende ZnS. We also study the spin-polarized electronic band structures, total and partial density of states and the effect of TM 3d states. Our results exhibit that Zn 0.75 Fe 0.25 S, Zn 0.75 Co 0.25 S and Zn 0.75 Ni 0.25 S are half-metallic ferromagnetic with a magnetic moment of 4 B , 3 B and 2 B , respectively. Furthermore, we calculate the TM 3d spin-exchange-splitting energies x (d), x (x−d), exchange constants N 0˛a nd N 0ˇ, crystal field splitting ( E cryst ≡ E t 2g − E eg ), and find that p-d hybridization reduces the local magnetic moment of TM from its free space charge value. Moreover, robustness of Zn 1−x TM x S with respect to the variation of lattice constants is also discussed.

Computational Materials Science, 2010

Magnetic and electronic structure calculations were carried out for WC-, MnP-, NaCl-and zinc blende (ZB)-type Mo and W based group V compounds, TMX (TM = Mo and W; X = N, P, As, Sb and Bi), using the tight-binding linear muffin-tin orbital (TB-LMTO) method. For these compounds in these four structures, the total energy has been calculated as a function of volume in spin-polarization and non-spinpolarization calculations. From the total energy calculations, it is observed that these compounds favour the structures for which there is octahedral coordination for the anion rather than tetrahedral coordination. For the large volume expansion, these compounds prefer tetrahedral coordination compared to octahedral coordination. Moreover, these compounds in the ZB-type structure are found to exhibit halfmetallic property with a magnetic moment of 3.00 l B per formula unit under expansion of volume. The equilibrium lattice constant, bulk modulus, heat of formation, magnetic moment, spin-flip-gap and minority spin bandgap are calculated and compared with available results. The band structure and density of states are presented.

The European Physical Journal B - Condensed Matter, 2004

The magnetic properties of the Zn2FeV3O11vanadate, characterized by a disordered distribution of diamagnetic Zn 2+ and high-spin Fe 3+ ions, are studied using magnetization and electron paramagnetic resonance (EPR) measurements. The dc susceptibility reveals antiferromagnetic interactions between Fe 3+ spins with a Curie-Weiss temperature Θ = −58(1) K, followed by a transition to a frozen, spin-glasslike state at low temperature T f ≈ 2.55 K, indicating an inhomogeneous magnetic ground state. The temperature variation of the EPR parameters confirms the antiferromagnetic coupling of Fe 3+ spins at high temperatures, while a distinct divergence is observed at T ≈ 55 K. This behavior is attributed to the inherent magnetic inhomogeneity of the system due to antiferromagnetic spin clusters.

Journal of Physics: Condensed Matter

The weak itinerant magnetic properties of A2Ni7 compounds with A = {Y, La} have been investigated using electronic band structure calculations in the relation with their polymorphic crystal structures. These compounds crystallizes in two structures resulting from the stacking of two and three blocks of [A2Ni4 + 2 ANi5] units for hexagonal 2H-La2Ni7 (Ce2Ni7 type) and rhombohedral 3R-Y2Ni7 (Gd2Co7 type) respectively. Experimentally, 2H-La2Ni7 is a weak itinerant antiferromagnet whereas 3R-Y2Ni7 is a weak itinerant ferromagnet. From the present first principles calculation within non-spin polarized state, both compounds present an electronic density of state with a sharp and narrow peak centered at the Fermi level corresponding to flat bands from 3d-Ni. This induces a magnetic instability and both compounds are more stable in a ferromagnetic (FM) order compared to a paramagnetic state (ΔE ≈-35 meV/f.u.). The magnetic moment of each of the five Ni sites varies with their positions relative to the [A2Ni4] and [ANi5] units: they are minimum in the [A2Ni4] unit and maximum at the interface between two [ANi5] units. For 2H-La2Ni7, an antiferromagnetic (AFM) structure has been proposed and found with an energy comparable to that of the FM state. This AFM structure is described by two FM unit blocks of opposite Ni spin sign separated by a non-magnetic layer at z = 0 and ½. The Ni (2a) atoms belonging to this intermediate layer are located in the [La2Ni4] unit and are at a center of symmetry of the hexagonal cell (P63/mmc) where the resultant molecular field is cancelled. Further non-collinear spin calculations have been performed to determine the Ni moment orientations which are found preferentially parallel to the c axis for both FM and AFM structures.