Direction Of Spin Alignment Research Articles

Hydrogen Atom Adsorption-Induced Spin Reversal and Vacancies Boosting Hydrogen Evolution Reaction in Defective H-VS2 Monolayers

Spin reversal induced by adsorbates will cause intersite communication between the active and adjacent sites, which modulates the exchange coupling strength and spin alignment direction of adjacent atoms. Here, spin reversal induced by H adsorption and hydrogen evolution reaction (HER) performance of defective H-VS2 are studied by density-functional theory. The spin of V/S atoms around double S vacancies on different atomic layers (V2S) exhibits continuous reversals with H adsorption, which reverses once for S atoms around single V vacancy (VV). Moreover, the adsorption energies of the second H atom decreased in V2S- and VV-modified H-VS2 systems. Additionally, V2S and VV can activate the inert basal plane of H-VS2, and the increased antibonding filling and p-band center in H-VS2 with VV will weaken the interaction between S–H atoms and promote the desorption of H2, which causes lower Gibbs free energy in H-VS2 with VV than V2S and the pure H-VS2 monolayer.

First principles study of magnetization and magnetic anisotropy energy of small Co-Pt clusters

The structural and magnetic properties of Co-Pt clusters up to five atoms with all possible combinations have been studied systematically. The global minimum energy structure of a cluster is obtained by optimizing its different possible geometries by using density functional theory (DFT) approximation. The electronic structure of the clusters were analyzed and found that the hybridization of 3d orbital of Co with the 5d orbital of Pt has enhancement effect on magnetization. The magnetic anisotropy energy of these small clusters is calculated from the free energy difference in two different noncolinear direction of spin alignment. It is found that the cluster with approximately equal number of Co and Pt atoms have larger anisotropy than the clusters with unequal number of Co and Pt of the same size. This can be explained by the combined effect of spin moment, orbital moment and the spin orbit coupling constant of the two materials.

Preparation and detection of states with simultaneous spin alignment and selectable molecular orientation in PbO

We are pursuing an experiment to measure the electric dipole moment of the electron using the molecule PbO. This measurement requires the ability to prepare quantum states with orientation of the molecular axis and, simultaneously, alignment of the electron spin perpendicular to this axis. It also requires efficient detection of the evolution of the spin alignment direction within such a state. We describe a series of experiments that have achieved these goals, and the features and limitations of the techniques. We also discuss possible new approaches for improved efficiency in this and similar systems.

Unbalanced spin accumulation induced by spin Hall effect

Moving electrons of different spins experience skew scattering in a two-dimensional electron gas layer and the electron deviates different direction due to the spin-dependent deflection. If spin is randomly oriented, the amount of skew scattering on both sides will be same and the Hall voltage will read zero. In this experiment, the carrier concentrations of spin up and down are unbalanced because the spin is aligned by stray field from the ferromagnet. Therefore, the voltage probe reads charge accumulation asymmetry. Spin Hall voltage is functions of the spin alignment direction and the amount of spin polarization.

Microstructure and magnetism in the ilmenite-hematite solid solution: A Monte Carlo simulation study

The energetics of magnetic and cation ordering have been modeled using an atomistic approach based on empirical exchange interaction parameters. The model has been applied to the study of magnetic and cation ordering in the ilmenite-hematite solid solution via Monte Carlo simulations, providing new insight into the effect of nanoscale microstructures on the magnetic properties of this system. The lowest energy state for intermediate compositions is an intergrowth of cation-disordered antiferromagnetic (AF) hematite and cation-ordered paramagnetic (PM) ilmenite, separated by mixed Fe2+/Fe3+ “contact layers”. The intergrowth carries a stable defect moment (“lamellar magnetism”) due to the presence of uncompensated spins. The net magnetization is parallel to the spin alignment direction, i.e., perpendicular to the spin-canted magnetization of the AF hematite. Contact-layer spins are coordinated to fewer magnetic neighbors than bulk spins and thus disorder more rapidly on heating. This leads to a decrease of net moment with increasing temperature. A small net moment is present, however, up to the Néel temperature of the AF hematite phase. The maximum temperature for acquisition of a chemical remanent magnetization due to lamellar magnetism is 800 ± 25 K, corresponding to the temperature for the eutectoid reaction PM hematite → AF hematite + PM ilmenite. If only cation interactions are considered, Fe3+ and Fe2+ in the contact layers become ordered so that Fe3+ shares an octahedral face with Fe3+ in the neighboring hematite layer and Fe2+ shares an octahedral face with Ti4+ in the neighboring ilmenite layer. If both cation and magnetic interactions are considered, however, an alternative ordering scheme is stabilized, whereby Fe3+ shares an octahedral face with Ti4+ in the neighboring ilmenite layer and Fe2+ shares an octahedral face with Fe3+ in the neighboring hematite layer.

Symmetry properties of theSmatrix in a fully relativistic distorted-wave treatment of electron-impact ionization

The symmetry properties of the $S$ matrix in a fully relativistic distorted-wave treatment of electron-impact ionization are investigated. It is shown that the square modulus of the scattering matrix element in which the spin states of all four electrons are determined is not invariant under the reversal of the direction of alignment of all spins. The largest of two contributions to this noninvariance originates from the relativistic modifications of the continuum wave functions induced by the distorting potential of the target atom. A second smaller contribution is manifested on reducing the eight-dimensional matrix elements of the QED covariant propagator to purely spatial two-electron integrals. The triple differential cross section (TDCS) exhibits a spin asymmetry unless the entire scattering process occurs in a single plane. There will be a difference in the TDCS between an $(e,2e)$ event in which the initial beam is polarized parallel or antiparallel with respect to the beam direction even if the target is unpolarized and the final spin states are not determined. The TDCS will remain unchanged if, in addition to reversal of the direction of spin alignment, one appropriate momentum component of one of the two outgoing electrons is reversed.

Mössbauer Study of the Direction of Spin Alignment in Oxalate-Bridged Metal Assemblies

The direction of spin alignment was investigated for three mixed crystal systems of molecule-based magnets, NBu4[Fe(II) x Mn(II)1−x Cr(III)(ox)3] (x = 0.03−1), NBu4 [Mn(II)Fe(III) x Cr(III)1− x(ox)3] (x = 0.04–1) and NBu4[Fe(II) x Ni(II)1− xFe(III)(ox)3] (x = 0 − 1), by using 57Fe Mössbauer spectroscopy, where NBu4 ± = tetra(n-butyl)ammonium ion and ox2− = oxalate ion. With the decrease of x, the direction of the internal magnetic field (H n) at Fe(II) nucleus in NBu4[Fe(II) x Mn(II)1−x Cr(III) (ox)3] was changed gradually from parallel to perpendicular, to the honeycomb layers consisting of an alternate array of the bivalent and tervalent ions through ox2− ligands; this indicates that the Mn(II) spin direction in NBu4[Mn(II)Cr(III)(ox)3] (x = 0) is almost perpendicular to the honeycomb layers. An approximately perpendicular spin alignment was also indicated for the Cr(III) ions in the same compound, from the x-dependence of the Fe(III) spin direction in NBu4[Mn(II)Fe(III) x Cr(III)1−x (ox)3]. A variation of ca. 50° in direction was observed for the H n at Fe(III) in NBu4[Fe(II) x Ni(II)1−x Fe(III)(ox)3].

Unexpected behavior of the antiferromagnetic mode of NiO

Although NiO is often considered the classic example of an antiferromagnetic insulator, recent investigations have revealed unexplained features of the magnon spectrum. The present study of the temperature and polarization behavior of first-order magnetic Raman scattering reveals that the polarization selection rules are not described by the generally accepted antisymmetric scattering tensor. The inclusion of quadratic magneto-optic coupling terms can explain the symmetry of the scattering tensor, but does not lead to results consistent with the accepted [112] spin alignment direction. {copyright} {ital 1998} {ital The American Physical Society}

Numerical Study of Weak Ferromagnetism in 2D J1-J2Heisenberg Model with Dzyaloshinskii-Moriya Interaction

By means of exact diagonalization we consider the groundstate of the J1—J2 spin 1/2 Heisenberg model with an anisotropic interaction term of Dzyaloshinskii—Moriya type. We find that a Dzyaloshinskii—Moriya interaction may create a weak ferromagnetic moment. The interplay between the quantum nature of the groundstate of the pure J1—J2 model and the anisotropic Dzyaloshinskii—Moriya interaction favour energetically a well-defined direction of spin alignment creating anisotropic correlations.

Conditioning infants by myoelectrically controlled reinforcement

The structural and magnetic properties of Co-Pt clusters up to five atoms with all possible combinations have been studied systematically. The global minimum energy structure of a cluster is obtained by optimizing its different possible geometries by using density functional theory (DFT) approximation. The electronic structure of the clusters were analyzed and found that the hybridization of 3d orbital of Co with the 5d orbital of Pt has enhancement effect on magnetization. The magnetic anisotropy energy of these small clusters is calculated from the free energy difference in two different noncolinear direction of spin alignment. It is found that the cluster with approximately equal number of Co and Pt atoms have larger anisotropy than the clusters with unequal number of Co and Pt of the same size. This can be explained by the combined effect of spin moment, orbital moment and the spin orbit coupling constant of the two materials.

Anomalous AFMR in some quasi-one-dimensional Mn2+compounds

Antiferromagnetic resonance experiments in the range 10< nu <60 GHz have been performed on a series of quasi-one-dimensional Mn2+ compounds with varying anisotropy. Pronounced deviations from classical AFMR theory are observed, in accordance with the experiments at higher frequencies reported by Tuchendler et al. (1981). These deviations show a substantial temperature dependence and seem to be related to the amount of anisotropy between the preferred and next-preferred direction of spin alignment. The experimental evidence will be compared with the results of a renormalised spin wave calculation.

Magneto-optical study of ferromagnetically coupled cobalt (II) pairs in cadmium bromide

Low temperature polarized absorption and magnetic circular dichroism spectra are reported for crystals of CdBr2 doped with varying concentrations of Co2+ in the region near 17 700 cm-1. Sharp zero phonon lines are identified as the trigonal field components of Ug ′(2 T 1g , 2 H) in dilute crystals, and as states arising from ferromagnetically coupled in-plane pairs in the concentrated ones. Measurements of the temperature dependence of the lines, and Zeeman spectra recorded with applied fields up to 50 kG parallel and perpendicular to the crystal c-axis, lead to estimates of the anisotropy of the exchange interaction in the ground state, and to both isotropic and anisotropic exchange in the excited state. The preferred direction of spin alignment in both states is parallel to the c-axis.

Band structure of nickel: Spin-orbit coupling, the Fermi surface, and the optical conductivity

A previous self-consistent calculation of energy bands in ferromagnetic nickel using the tight-binding method has been extended to include spin-orbit coupling. Exchange was incorporated using the $X\ensuremath{\alpha}$ method with $\ensuremath{\alpha}=\frac{2}{3}$. Energy levels were obtained at 1357 points in 1/16th of the Brillouin zone. The direction of spin alignment was taken to be [001]. The density of states was computed by a hybrid method. Cross sections of the Fermi surface were determined, and effective masses were obtained. The interband contribution to the conductivity tensor was calculated using matrix elements computed from wave functions including spin-orbit coupling. Results were obtained for both the diagonal and the off-diagonal elements of the conductivity tensor.

Green Functions in the Theory of Antiferromagnetism

A Green function method has been used to treat the statistics of a general antiferromagnetic structure with arbitrary spin value per site and with Heisenberg exchange interactions between any or all pairs of spins in the system. The only restrictions placed upon the type of order are that there shall be a single direction of spin alignment and that each of the two ferromagnetic sublattices shall be translationally invariant. Expressions are given for the sublattice magnetization and N\'eel temperature and, as a particular application of the results, the N\'eel temperatures for certain face-centered cubic orders are calculated explicitly. The behavior of a general antiferromagnetic structure in the presence of an external magnetic field is also examined. Expressions are derived for the parallel and perpendicular magnetic susceptibilities, and are discussed in detail at low and high temperatures and also at the N\'eel point.

Magnetic Dipolar Interactions in MnO and in Ferrites

The magnetic dipole energies of MnO and of the normal and inverse spinel structures are calculated. It is found that with this interaction alone MnO would have its direction of spin alignment in a (111) plane, in contrast to the experimentally found [100]. The addition of a nearest neighbor quadrupole interaction is suggested as a means of making the [100] direction preferred. The normal and the inverse spinel structures are found to have zero magnetic dipole energies.