We measured high-quality Co 2p magnetic circular dichroism (MCD) spectra in photoemission for > 5 ML Co films grown on Cu(1 1 13) using a “complete” experiment,
where the sample magnetization and the light helicity vector were reversed separately. We show how the four measured spectra,
M±P±, can be used to make new linear combinations, which correspond to the circular dichroism in the angular dependence (CDAD),
magnetic linear dichroism in the angular dependence (MLDAD) and MCD spectra. The integrated signals of the MLDAD and CDAD
can be used to estimate the error caused by the difference in the degrees of magnetization and light polarization, respectively,
in the opposite alignments. The MCD signal integrated over the entire 2p region does not average to zero, as one would have expected from the sum rule for photoemission to a non-interacting continuum
state. There is a strong MCD signal in the entire region between the 2p3/2 and 2p1/2 main lines with pronounced satellite structure. The differences between the measured and calculated results for an independent-particle
and an atomic model indicate the presence of interatomic electron correlation effects and configurational mixing.
Received 26 September 2000 相似文献
We report on X-ray magnetic diffraction studies of the spin density wave antiferromagnetism formed in the conduction electron
band of chromium. Non-resonant X-ray magnetic scattering was used to directly determine that chromium has zero orbital magnetisation.
Furthermore, the azimuthal dependence of this scattering provides unique evidence that chromium forms a linearly polarised
wave. In the vicinity of the K absorption edge, resonant X-ray magnetic scattering was observed. A consistent model of the
magnetic scattering has been derived from the resonant and non-resonant magnetic amplitudes. The enhancement of the magnetic
intensity arises primarily from dipole transitions from the core 1s level to 4p states. Quadrupole transitions to the magnetic 3d states are essentially non-existent due to their sensitivity to (and the absence of) orbital moment. This effect is predicted
from atomic considerations of the 3d5 ( = 0) transition metal ions.
Received 22 September 2000 相似文献
We report on X-ray resonance exchange and neutron scattering of metallic GdS. At the LII and L III absorption edges of Gd, resonance enhancements of more than two orders of magnitude over the non-resonant magnetic scattering
are observed. Polarisation analysis proves that these enhancements are due to dipolar transitions from the 2p to the 5d states. The branching ratio between the LII and L III edges of 2.5 suggests a polarisation of the 5d electrons in the ground state. The antiferromagnetic order is of type II in the fcc lattice. Single crystal diffraction of
hot neutrons suggests that the spin direction lies within the (111) planes with a value for the sublattice magnetisation of
6.51(3) . The critical exponent for the sublattice magnetisation has a value of β = 0.38(2) in agreement with a pure Heisenberg model.
Above TN, a sharp component persists in the critical diffuse scattering. Lattice distortions give indications for two additional low-temperature
phase transitions at about 49 K and 32 K. We argue that these transitions are not connected to spin reorientations and discuss
the possible influence of fourth-order exchange interactions.
Received 19 November 1999 and Received in final form 12 December 2000 相似文献
The phase diagram of half-doped manganite systems of formula A0.5A′0.5MnO3 is investigated within a single-orbital model incorporating magnetic double-exchange and superexchange, together with intersite
Coulomb and electron-lattice interactions. Strong Jahn-Teller and breathing mode deformations compete together and result
in shear lattice deformations. The latter stabilize the charge-ordered CE-type phase, which undergo first-order transitions
with temperature or magnetic field to either Ferromagnetic metallic or Paramagnetic insulating phases. An essential feature
is the self-consistent screening of Coulomb and electron-phonon interactions in the ferromagnetic phase.
Received 28 November 2000 相似文献
Summary: Three‐dimensionally ordered macroporous (3DOM) syndiotactic polystyrenes with pore size in the range of 71–286 nm were fabricated by means of silica templates using (dbm)2Ti(OPh)2/MAO catalytic system. The resulting materials were characterized by NMR, SEM, powder X‐ray diffraction, GPC and DSC. The results indicated that the 3DOM syndiotactic polystyrenes were highly syndiotactic, and the pore contraction increased when the average pore diameter decreased. Compared with bulk syndiotactic polystyrenes, 3DOM syndiotactic polystyrene possessed lower molecular weight, narrower molecular weight distribution, and lower crystallinity and melting temperature.
SEM image of 3DOM syndiotactic polystyrene, the inset shows the detail of the cavities. 相似文献
In this paper, we establish a theorem of the alternative in ordered linear topological spaces. Then, optimality conditions for the optimization of set-valued maps are obtained. 相似文献
Nonparametric factorial designs for multivariate observations are considered under the framework of general rank-score statistics. Unlike most of the literature, we do not assume the continuity of the underlying distribution functions. The models studied include general repeated measures designs, compound symmetry designs, and designs for longitudinal data. In particular, designs for ordered categorical data are included. The vectors of the multivariate observations may have different lengths. Moreover, our general framework includes missing values and singular covariance matrices which occur quite frequently in practical data analysis problems. The asymptotic properties of the proposed statistics are studied under general nonparametric hypotheses as well as under a sequence of nonparametric contiguous alternatives. L2-consistent estimators for the unknown covariance matrices are given and two types of quadratic forms are considered for testing the nonparametric hypotheses. The results are applied to a two-way mixed model assuming compound symmetry and to a factorial design for longitudinal data. The main idea of the proofs is based on some moment inequalities for empirical distribution functions in mixed models. The details are provided in the Appendix. 相似文献
Ho0.1Ca0.9MnO3 is a canted antiferromagnet with the magnetic space group Pn'ma'. The magnetic structure is a superposition CxFyAz of the three types of order allowed in Pn'ma'. In the Ca-rich corner of the system Ho1-xCaxMnO3 the title compound has a strong magnetoelastic distortion , the highest metallic conductivity and a ferromagnetic component Fy close to the maximum in the series. Among the areas ab, bc, ca calculated from the lattice constants only ca shows a strong magnetoelastic effect below TN = 106 K. The x-, y-, z-spin components depend differently on the temperature. This gives rise to spin rotation which is particularly strong close
to TN. MnO6 octahedra have short bond lengths with a temperature independent average . They are practically regular at room temperature and show a Jahn-Teller distortion of 3.5% in the magnetically ordered state.
Above TN we find small polaron conductivity. The presence of the Jahn-Teller distortion due to the only small abundance (10%) of Mn3+ in the t2g3eg configuration is attributed to delocalised eg electrons. In the magnetically ordered state the averaged magnetic moment of Mn is reduced appreciably from the paramagnetic
value due to spin disorder.
Received 21 January 1999 相似文献
We study the effects of finite temperature on the dynamics of non-planar vortices in the classical, two-dimensional anisotropic
Heisenberg model with XY- or easy-plane symmetry. To this end, we analyze a generalized Landau-Lifshitz equation including additive white noise and
Gilbert damping. Using a collective variable theory with no adjustable parameters we derive an equation of motion for the
vortices with stochastic forces which are shown to represent white noise with an effective diffusion constant linearly dependent
on temperature. We solve these stochastic equations of motion by means of a Green's function formalism and obtain the mean
vortex trajectory and its variance. We find a non-standard time dependence for the variance of the components perpendicular
to the driving force. We compare the analytical results with Langevin dynamics simulations and find a good agreement up to
temperatures of the order of 25% of the Kosterlitz-Thouless transition temperature. Finally, we discuss the reasons why our
approach is not appropriate for higher temperatures as well as the discreteness effects observed in the numerical simulations.
Received: 27 April 1998 / Revised: 2 September 1998 / Accepted: 10 September 1998 相似文献