Moment Of Transition Metal Research Articles

First principle investigation on properties of MnO2 as an electrode material for Li, Na, Mg, and Al -ion batteries

This study uses noble evaluations in Density Functional Theory (DFT) framework to investigate the structural, electrochemical, magnetic, and electrical properties of AMn2O4 (A = Li, Na, Mg, and Al) cathode materials for various metal-ion batteries. The calculations are performed by four DFT methods (GGA/+U, LSDA/+U). Considering volume change Both GGA and LSDA methods showed that NaMn2O4 had the highest and AlMn2O4 had the lowest volume reduction, caused by electronegativity of Al and the initial unit cell volume. The cell voltages were calculated with two different approaches called as internal and Fermi energy. It was concluded that the probable low cycle-ability of this family can be attributed to remarkable alteration of magnetic moment of manganese transition metal during extraction/insertion of intercalating ions. The electrical properties of AMn2O4 materials were investigated evaluating BGs and electrical rate-capability. For each material two kinds of band-gap (BG) and two criterions for rate-capability were considered, i.e. ILBG/ELBG, and Delta/CCTB, respectively. The BG evaluation showed that all the considered materials have appropriate conductivity. Both of the evaluated Delta and CCTB approaches predicted high rate-capability for the AMn2O4 materials. Our calculations demonstrated that MnO2 is a suitable and highly considerable cathode material for the Li and beyond-Li -ion batteries.

Effect of Ni Substitution on the Structural, Magnetic, and Electronic Structure Properties of Gd0.4Tb0.6(Co1-xNix)2 Compounds.

The comprehensive research of magnetic and electronic structure properties of the new class of Gd0.4Tb0.6(Co1-xNix)2 compounds, crystallizing in the cubic Laves phase (C15), is reported. The magnetic study was completed with electrical resistivity and electronic structure investigations. The analysis of Arrott plots supplemented by a study of temperature dependency of Landau coefficients revealed that all compounds undergo a magnetic phase transition of the second type. Based on magnetic isotherms, magnetic entropy change (ΔSM) was determined for many values of the magnetic field change (μ0H), which varied from 0.1 to 7 T. For each compound, the ΔSM had a maximum around the Curie temperature. Both values of the |ΔSMmax| and relative cooling power RCP parameters increased with increasing nickel content. It is shown that structural disorder upon Co/Ni substitution influences some magnetic parameters. The magnetic moment values of Co atoms determined from different methods are quantitatively consistent. From the M(T) dependency, the exchange integrals JRR, JRT, and JTT between rare-earths (R) and transition metal (T) moments were evaluated within the mean-field theory (MFT) approach. The experimental study of the electronic structure performed with the use of the X-ray photoelectron spectroscopy (XPS) was completed by calculations using the full-potential linearized augmented plane waves (FP-LAPW) method based on the density functional theory (DFT). The calculations explained experimentally observed changes in the XPS valence band spectra upon the Ni/Co substitution.

Charge Compensation Mechanisms and Oxygen Vacancy Formations in LiNi1/3Co1/3Mn1/3O2: First-Principles Calculations.

Charge compensation mechanisms in the delithiation processes of LiNi1/3Co1/3Mn1/3O2 (NCM111) are compared in detail by the first-principles calculations with GGA and GGA+U methods under different U values reported in the literature. The calculations suggested that different sets of U values lead to different charge compensation mechanisms in the delithiation process. Co3+/Co4+ couples were shown to dominate the redox reaction for 1 ≥ x ≥ 2/3 by using the GGA+U1 method (U1 = 6.0 3.4 3.9 for Ni, Co, and Mn, respectively). However, by using the GGA+U2 (U2 = 6.0 5.5 4.2) method, the results indicated that the redox reaction of Ni2+/Ni3+ took place in the range of 1 ≥ x ≥ 2/3. Therefore, according to our study, experimental charge compensation processes during delithiation are of great importance to evaluate the theoretical calculations. The results also indicated that all the GGA+Ui (i = 1, 2, 3) schemes predicted better voltage platforms than the GGA method. The oxygen anionic redox reactions during delithiation are also compared with GGA+U calculations under different U values. The electronic density of states and magnetic moments of transition metals have been employed to illustrate the redox reactions during the lithium extractions in NCM111. We have also investigated the formation energies of an oxygen vacancy in NCM111 under different values of U, which is important in understanding the possible occurrence of oxygen release. The formation energy of an O vacancy is essentially dependent on the experimental conditions. As expected, the decreased temperature and increased oxygen partial pressure can suppress the formation of the oxygen vacancy. The calculations can help improve the stability of the lattice oxygen.

Uncompensated Spin Magnetic Moment and Properties of Coordination Bond M ← OH2 in Isostructural Nitrilo-tris-Methylenephosphonate Complexes [MII(H2O)3μ-NH(CH2PO3H)3] (MII = Cr–Zn)

The parameters of coordination bonds M ← OH2 (the magnetic moments of transition metals, interatomic distances, force constants, and break energies) in isostructural nitrilo-tris-methylenephosphonate complexes of transition metals of 3d-series [MII(H2O)3μ–NH(CH2PO3H)3] (MII = Cr–Zn) are analyzed. It is shown that the correlation of force constants with interatomic distances is in good agreement with the Badger rule, and the break energy of bond M ← OH2 deviates strongly from the empirical Poling dependence. It is shown that deviations of the break energy of bond M ← OH2 from the Poling rule are due to the presence of an uncompensated spin density at the central atom. This explains the stability of Fe-containing heterometallic coordination polymers [(Fe,M)(H2O)3μ–NH(CH2PO3H)3], which determines the high efficiency of nitrilo-tris-methylenephosphonate complexes as inhibitors of the corrosion of steel in aqueous media.

Magnetic inversion symmetry breaking and spin reorientation in Tb2MnNiO6 : A polar strong ferromagnet

We report a description and comprehensive study on four successive magnetic transitions in ferromagnetic $\mathrm{T}{\mathrm{b}}_{2}\mathrm{MnNi}{\mathrm{O}}_{6}$ double perovskite. In the ground state ($P{2}_{1}^{\ensuremath{'}}$), the moments of magnetic $A$ and $B$ sites order according to different nonpolar magnetic modes, but the coupling between them generates an overall polar symmetry which makes this oxide potentially multiferroic due to magnetic trilinear coupling, and therefore ferromagnetic and ferroelectric in its ground state. Its macroscopic magnetization is large ($5\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{f}.\mathrm{u}$) and not related to a weak ferromagnetic component induced by Dzyaloshinskii-Moriya interaction. However, a sharp and severe spin reorientation of the ferromagnetic transition-metal moments has been observed which opens the door to the magnetic switching of the ferroelectric state in this perovskite, and conversely to the control of the magnetization direction by electrical fields applied parallel to $b$. We also anticipate that in this material the direction of the magnetization (towards $c/a$) could be used as the key to switch the polar/nonpolar (ferroelectric/antiferroelectric) transformation.

Computationally predicting spin semiconductors and half metals from doped phosphorene monolayers

First-principles computations are performed to investigate phosphorene monolayers doped with 30 metal and nonmetal atoms. The binding energies indicate the stability of all doped configurations. Interestingly, the magnetic atom Co doping induces the absence of the magnetism while the magnetism is realized in phosphorene with substitutional doping of nonmagnetic atoms (O, S, Se, Si, Br, and Cl). The magnetic moment of transition metal (TM)-doped systems is suppressed in the range of 1.0–3.97 µB. The electronic properties of the doped systems are modulated differently; O, S, Se, Ni, and Ti doped systems become spin semiconductors, while V doping makes the system a half metal. These results demonstrate potential applications of functionalized phosphorene with external atoms, in particular to spintronics and dilute magnetic semiconductors.

Structural and magnetic properties ofGdCo5−xNix

GdCo$_5$ may be considered as two sublattices - one of Gd and one of Co - whose magnetizations are in antiparallel alignment, forming a ferrimagnet. Substitution of nickel in the cobalt sublattice of GdCo$_5$ has been investigated to gain insight into how the magnetic properties of this prototype rare-earth/transition-metal magnet are affected by changes in the transition metal sublattice. Polycrystalline samples of GdCo$_{5-x}$Ni$_x$ for 0 $ \leq x \leq $ 5 were synthesized by arc melting. Structural characterization was carried out by powder x-ray diffraction and optical and scanning electron microscope imaging of metallographic slides, the latter revealing a low concentration of Gd$_2$(Co, Ni)$_7$ lamellae for $x \leq 2.5$. Compensation - i.e. the cancellation of the opposing Gd and transition metal moments is observed for $1 \leq x \leq 3$ at a temperature which increases with Ni content; for larger $x$, no compensation is observed below 360 K. A peak in the coercivity is seen at $x \approx 1$ at 10K coinciding with a minimum in the saturation magnetization. Density-functional theory calculations within the disordered local moment picture reproduce the dependence of the magnetization on Ni content and temperature. The calculations also show a peak in the magnetocrystalline anisotropy at similar Ni concentrations to the experimentally observed coercivity maximum.

Realizing Two-Dimensional Magnetic Semiconductors with Enhanced Curie Temperature by Antiaromatic Ring Based Organometallic Frameworks.

Two-dimensional (2D) magnetic semiconductors with room-temperature ferromagnetism are very desirable. Despite the great progress made recently, the Curie temperature is still very low (∼45 K), originating from the weak ferromagnetic superexchange interaction. Here, based on first-principles calculations, we propose a general route to achieve 2D magnetic semiconductors with enhanced Curie temperature in organometallic frameworks by incorporating antiaromatic rings as organic linkers. Antiaromatic rings usually possess low-energy multiple spin states, which can be easily induced by adjacent magnetic moments of transition metals and subsequently coupled with them through the strong d-p direct exchange interaction, producing high-temperature ferrimagnetic ordering. The design of 2D organometallic frameworks with typical antiaromatic rings such as pentalene, which show Curie temperatures well above room temperature from classic Heisenberg model Monte Carlo simulations, confirms our proposal.

Magnetic, Magnetocaloric Properties, and Phenomenological Model in Amorphous Ni80−xFex(SiB)20 Alloys with (x = 0, 2.4, 8, and 16)

Amorphous Ni80−xFex(SiB)20 ribbons with different Fe concentrations (0 ≤ x ≤ 16) were fabricated by melt spinning technique, and their magnetic and magnetocaloric properties were investigated and a phenomenological model was also applied. The Curie temperature (TC), magnetic moment of transition metal and maximum magnetic entropy change (− ΔSM) increase with increasing Fe content. At a magnetic field change of 2 T, the (− ΔSM) and relative cooling power (RCP) show the highest values of 0.53 J/kg K and 85 J kg−1 respectively for Fe16Ni64(SiB)20 alloys. In addition, a satisfactory agreement between the experimental and Hamad’s phenomenological model is reported.

Exchange Interactions and Transition Metal Moments in Rare-Earth Compounds

Band structure calculations have been performed on heavy rare-earths R2Fe17 compounds. The iron moments are strongly dependent on the site location and little influenced by the rare-earth partner. The Curie temperatures follow a linear trend as function of R5d band polarizations. The magneto-volume effects are well described in models where the iron moments have a rather great degree of localization. The magnetic properties of GdFe2, at high pressures, were theoretically analysed. Both magnetic and structure transitions have been suggested, as the pressure increases.

The distribution alloying elements in alnico 8 and 9 magnets: Site preference of ternary Ti, Fe, Co, and Ni additions in DO3 Fe3Al, Co3Al, and Ni3Al based intermetallic phases

Recently, interest in alnico magnetic alloys has been rekindled due to their potential to substitute for rare-earth based permanent magnets provided modest improvements in their coercivity can be achieved without loss of saturation magnetization. Recent experimental studies have indicated that atomic and magnetic structure of the two phases (one AlNi-based, the other FeCo-based) that comprise these spinodally decomposed alloy is not as simple as previously thought. A key issue that arises is the distribution of Fe, Co, and Ti within the AlNi-based matrix phase. In this paper, we report the results of first-principles calculations of the site preference of ternary alloying additions in DO3 Fe3Al, Co3Al, and Ni3Al alloys, as models for the aluminide phase. For compound compositions that are Al rich, which correspond to experimental situation, Ti and Fe are found to occupy the α sites, while Co and Ni prefer the γ sites of the DO3 lattice. An important finding is that the magnetic moments of transition metals in Fe3Al and Co3Al are ordered ferromagnetically, whereas the Ni3Al were found to be nonmagnetic unless the Fe or Co is added as a ternary element.

Searching for room temperature ferromagnetism in transition metal implanted ZnO and GaN

Significant progress in the field of wide-gap dilute magnetic semiconductors (DMS) depends on the discovery of a material system which not only shows high-temperature ferromagnetism but is also simple to prepare and thus easy to reproduce. In this context, ion implantation is an attractive doping method, being both relatively simple and highly reproducible. Here, we report on the search for high-temperature ferromagnetism in ZnO and GaN implanted with Mn, Fe, and Co, prepared under a wide range of implantation and post-processing conditions. We focused on the low concentration regime (∼0.3−4%) in order to avoid phase segregation and applied strict experimental procedures to avoid ferromagnetic contamination. Despite the wide range of materials, implantation and post-processing conditions, none of the DMS systems showed room-temperature ferromagnetism. These results support the view that dilute transition-metal moments do not order ferromagnetically in ZnO and GaN.

The 13-atom encapsulated gold cage clusters

The structure and the magnetic moment of transition metal encapsulated in a Au12 cage cluster have been studied by using the density functional theory. The results show that all of the transition metal atoms (TMA) can embed into the Au12 cage and increase the stability of the clusters except Mn. Half of them have the Ih or Oh symmetry. The curves of binding energy have oscillation characteristics when the extra-nuclear electrons increase; the reason for this may be the interaction between parity changes of extra-nuclear electrons and Au atoms. The curves of highest occupied molecular orbital—lowest unoccupied molecular orbital (HOMO—LUMO) gap also have oscillation characteristics when the extra-nuclear electrons increase. The binding energies of many M@Au12 clusters are much larger than that of the pure Au13 cluster, while the gaps of some of them are less than that of Au13, so maybe Cr@Au12, Nb@Au12, and W@Au12 clusters are most stable in fact. For magnetic calculations, some clusters are quenched totally, but the Au13 cluster has the largest magnetic moment of 5 μB. When the number of extra-nuclear electrons of the encapsulated TMA is even, the magnetic moment of relevant M@Au12 cluster is even, and so are the odd ones.

Existence of Two Concomitant Magnetic Structures Below TNéelfor the Natrochalcite, NaFeII2(H3O2)(MoO4)2

A comparative study of the magnetic properties and magnetic structures of the natrochalcite, NaFe(2)(D(3)O(2))(MoO(4))(2) (FeD) to those of the isostructural NaCo(2)(D(3)O(2))(MoO(4))(2) (CoD) and NaNi(2)(D(3)O(2))(MoO(4))(2) (NiD) is presented. The structural change is a shrinking of the unit cell in the order of the ionic radii of the transition metal, FeD > CoD > NiD. While NiD and CoD are canted-antiferromagnets with T(N) = 28 and 21 K, respectively, FeD is an anisotropic 2D-Ising antiferromagnet (T(N) = 17 K) with a spin-flop field of 14 kOe at 2 K and the presence of a hysteresis loop reaching only (1)/(4) of the saturation magnetization in 70 kOe. The critical field decreases almost linearly on warming to T(N). The neutron diffraction patterns of FeD below T(N) display numerous magnetic Bragg peaks which cannot be assigned to any one magnetic structure but fits well to two superposed sets, one with a temperature independent line width and has a propagation vector k(1) = (0, 0, 0) while for the other there is a clear dependence and k(2) = (0, 0, ½). In the k(1) = (0, 0, 0) magnetic structure the moments are parallel to each other within one chain and lie along the a-axis but are antiparallel to those in neighboring chains. In contrast CoD and NiD, for which k = (0, 0, 0), have their moments aligned along the b-axis and ac-plane, respectively. The second magnetic structure, k(2) = (0, 0, ½), is characterized by four sublattices, two per layer, where the moments are in the ab-plane and canted with a resultant along the a-axis which is compensated by those of the adjacent layers. For the k(2) = (0, 0, ½) structure, the scattering coherent length decreases, and the moments tend progressively toward the a-axis upon increasing temperature. The coexistence of two concomitant magnetic structures is unprecedented for compounds containing transition metal moment carriers.

Structural, Electronic, and Magnetic Properties of Neutral and Charged Transition Metal–Bis(dicarbollide) Sandwich Clusters

Structural, electronic, and magnetic properties of transition metal (TM)–bis(dicarbollide) (TM(Dcb)2; TM = Sc–Mn, Dcb = dicarbollide) sandwich clusters and their charged counterparts (TM(Dcb)2+, TM(Dcb)2–) are systematically investigated by using all electron density functional theory approach. All TM(Dcb)2 sandwich clusters are highly stable because of the formation of ionic–covalent bonding. The Ti(Dcb)2 is the most stable, the Sc- and V(Dcb)2 are intermediate, and the Cr- and Mn(Dcb)2 are the least stable. The magnetic moment of TM(Dcb)2 exhibits a clear element-dependent variation with 1 μB for Sc(Dcb)2 and 0 μB for Ti(Dcb)2 and with a linear increased trend by 1 μB from Ti(Dcb)2 to Mn(Dcb)2. This element-dependent magnetic behavior can be well understood by electron transfer as well as spin density distribution. We further reveal that charging can induce the rotation of the ligands in the Sc-, V-, Cr-, and Mn(Dcb)2 clusters, which makes them promising candidates for molecular motors.

Observation of a Novel Orbital Selective Mott Transition inCa1.8Sr0.2RuO4

We observed a novel orbital selective Mott transition in Ca(1.8)Sr(0.2)RuO(4) by angle-resolved photoemission. While two sets of dispersing bands and the Fermi surface associated with the doubly degenerate d(yz) and d(zx) orbitals are identified, the Fermi surface associated with the wider d(xy) band is missing as a consequence of selective Mott localization. Our theoretical calculations demonstrate that this orbital selective Mott transition is mainly driven by the combined effects of interorbital carrier transfer, superlattice potential, and orbital degeneracy, whereas the bandwidth difference plays a less important role.

Mössbauer effect studies of Dy(Fe 0.4Co 0.6− xNi x) 2 intermetallics

A consequence of Co/Ni substitution in the intermetallics Dy(Fe 0.4Co 0.6− x Ni x ) 2 was tested in this paper. Fe 57 Mössbauer effect measurements for the intermetallic system were carried out at 4.2 K and the determined hyperfine interaction parameters as functions of composition are reported. The magnetic hyperfine field as well as the Curie temperature is strongly reduced with a composition parameter x. Band structure calculations using the full-potential linearized augmented plane waves (FLAPW) method were performed. Some properties of the 3d bands of the Fe, Co and Ni constituents are discussed. The 3d band splitting energies and the magnetic moments of transition metals reduce with x. The experimentally determined magnetic hyperfine field correlates linearly with the calculated stoichiometrically weighted magnetic moment of 3d atoms and correlates linearly with the weighted splitting energy between 3d subbands. The Curie temperature changes nonlinearly with the squared magnetic hyperfine field or with the calculated squared weighted splitting energy between 3d subbands.

Local electronic structure and magnetic properties of 3d transition metal doped GaAs

The local electronic structure and magnetic properties of GaAs doped with 3d transition metal (Sc, Ti, V, Cr, Mn, Fe, Co, Ni) were studied by using discrete variational method (DVM) based on density functional theory. The calculated result indicated that the magnetic moment of transition metal increases first and then decreases, and reaches the maximum value when Mn is doped into GaAs. In the case of Mn concentration of 1.4%, the magnetic moment of Mn is in good agreement with the experimental result. The coupling between impure atoms in the system with two impure atoms was found to have obvious variation. For different transition metal, the coupling between the impure atom and the nearest neighbor As also has different variation.

Perpendicular magnetic anisotropy in TbFeCo films studied by magnetic Compton scattering

Magnetic Compton profiles (MCPs) of TbFeCo amorphous films have been measured from a viewpoint of perpendicular magnetic anisotropy (PMA). Analysis of anisotropies of the MCPs has shown that anisotropies of wave functions are small in both a PMA film and an isotropic magnetization (IM) film. Element selective analysis of the MCPs has shown that a Tb magnetic moment and a magnetic moment of 3d transition metal (TM) are coupled antiparallel in the PMA film. In the case the IM film, the magnetic moment of 3d TM tends to align toward the magnetic field but the Tb magnetic moment distributed to random orientations. The PMA natures reflect the magnetic structures of the Tb magnetic moment and the 3d TM magnetic moment in the TbFeCo films.

Calculation of spin and orbital moments of 3d transition metals using X-ray magnetic circular dichroism in absorption

X-ray magnetic circular dichroism(XMCD) in absorption has been extensively used to determine spin and orbital moments by applying the sum rules to the absorption spectra of specified atoms. Due to quench of orbital moments in 3d transition metals, it is necessary to reduce errors in experiments and data analysis. In this article we focas on the data analysis in 4 aspects. 1) The influence of applied magnetic field H on signal intensity. Experiments reveal that, for H-α; for H>200Gs, it changes little with the increase of H. 2) There is a separation between absorption spectra resulting from the iron-core remanence being in the parallel or antiparallel directions. This separation is independent of incident X-ray polarization and can be eliminated by multiplying by a constant. 3) An analytic form of absorption spectrum was obtained by fitting experimental data using XPSPEAK 4.1. It can be used as a criterion to determine which numerical integration method is suitable under certain experimental conditions. And, 4) by choosing an error function as a background to be subtracted from the X-ray absorption spectra, a method of calculation of spin and orbital moments from XMCD absorption spectrum is also developed Finally, the spin moment, of 1.314μB and orbital moment of 0.141μB of cobalt atom in a 20nm thick cobalt film are figured out based on Bode rule numerical integration.