1,946 research outputs found
Direct determination of the spin structure of NdIrO by means of neutron diffraction
We report on the spin structure of the pyrochlore iridate NdIrO
that could be directly determined by means of powder neutron diffraction. Our
magnetic structure refinement unravels a so-called all-in/all-out magnetic
structure that appears in both, the Nd and the Ir sublattice. The ordered
magnetic moments at 1.8 K amount to 0.34(1) /Ir and
1.27(1) /Nd. The Nd moment size at 1.8 K is
smaller than that expected for the Nd ground state doublet. On the other
hand, the size of the ordered moments of the Ir ions at 1.8 K agrees
very well with the value expected for a = 1/2 state based on
the presence of strong spin-orbit coupling in this system. Finally, our
measurements reveal a parallel alignment of the Nd moments with the net
moment of its six nearest neighboring Ir ions.Comment: http://journals.aps.org/prb/pdf/10.1103/PhysRevB.94.16110
Hour-glass magnetic spectrum in a stripe-less insulating transition metal oxide
An hour-glass shaped magnetic excitation spectrum appears to be an universal
characteristic of the high-temperature superconducting cuprates. Fluctuating
charge stripes or alternative band structure approaches are able to explain the
origin of these spectra. Recently, an hour- glass spectrum has been observed in
an insulating cobaltate, thus, favouring the charge stripe scenario. Here we
show that neither charge stripes nor band structure effects are responsible for
the hour-glass dispersion in a cobaltate within the checkerboard charge ordered
regime of La2-xSrxCoO4. The search for charge stripe ordering reflections
yields no evidence for charge stripes in La1.6Sr0.4CoO4 which is supported by
our phonon studies. With the observation of an hour-glass-shaped excitation
spectrum in this stripe-less insulating cobaltate, we provide experimental
evidence that the hour-glass spectrum is neither necessarily connected to
charge stripes nor to band structure effects, but instead, probably intimately
coupled to frustration and arising chiral or non-collinear magnetic
correlations
Multiferroicity in the frustrated spinel cuprate GeCuO
Different from other magnetically frustrated spinel systems,
GeCuO is a strongly tetragonal distorted spinel cuprate in which
edge-sharing CuO ribbons are running along alternating directions
perpendicular to the -axis. Here, GeCuO samples of high quality
were prepared via high pressure synthesis (at 4 GPa) and the corresponding
magnetic and dielectric properties were investigated. For the first time, we
observed a ferroelectric polarization emerging at T 33~K. Although
the ferroelectric polarization is weak in GeCuO (
0.2C/m), the existence of spin-induced multiferroicity provides a
strong constraint on the possible ground state magnetic structures and/or the
corresponding theoretical models of multiferroicity for GeCuO.Comment: https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.2.04140
A heterogeneous-agent model with district-level constraints: an application to livestock development in Gansu, China
This paper develops a heterogeneous-agent model to assess the impacts of removing lucerne growing subsidies, increasing livestock numbers and including district-level equilibrium conditions on optimal farm plans in the Qingyang district of Gansu Province, China. The model is a five-year dynamic linear program that solves across 96 farm households whilst incorporating district-level constraints. The approach used allows us to observe seasonal variations in incomes, infer the distribution of a policy shock among households and highlight trade patterns at the district level. The results suggest that without lucerne growing subsidies the total area of lucerne grown by all modelled households falls by 18%. Increasing livestock numbers by 25% reduces net household incomes by 17% as changes to labour allocations reduce off-farm employment opportunities. When external trade in forages is included in the model, total livestock numbers held by all 96 households rise from 502 to 838, this highlights the benefits of integrated feed markets. Shadow prices for crop production rise when livestock numbers increase, implying that benefits exist to improving crop yields.Heterogeneous-agent model, district-level constraints, livestock, China., Farm Management,
Magnetostrictive Neel ordering of the spin-5/2 ladder compound BaMn2O3: distortion-induced lifting of geometrical frustration
The crystal structure and the magnetism of BaMnO have been studied by
thermodynamic and by diffraction techniques using large single crystals and
powders. BaMnO is a realization of a spin ladder as the
magnetic interaction is dominant along 180 Mn-O-Mn bonds forming the
legs and the rungs of a ladder. The temperature dependence of the magnetic
susceptibility exhibits well-defined maxima for all directions proving the
low-dimensional magnetic character in BaMnO. The susceptibility and
powder neutron diffraction data, however, show that BaMnO exhibits a
transition to antiferromagnetic order at 184 K, in spite of a full frustration
of the nearest-neighbor inter-ladder coupling in the orthorhombic
high-temperature phase. This frustration is lifted by a remarkably strong
monoclinic distortion which accompanies the magnetic transition.Comment: 9 pages, 8 figures, 2 tables; in V1 fig. 2 was included twice and
fig. 4 was missing; this has been corrected in V
Verwey transition in FeO thin films: Influence of oxygen stoichiometry and substrate-induced microstructure
We have carried out a systematic experimental investigation to address the
question why thin films of FeO (magnetite) generally have a very broad
Verwey transition with lower transition temperatures as compared to the bulk.
We observed using x-ray photoelectron spectroscopy, x-ray diffraction and
resistivity measurements that the Verwey transition in thin films is
drastically influenced not only by the oxygen stoichiometry but especially also
by the substrate-induced microstructure. In particular, we found (1) that the
transition temperature, the resistivity jump, and the conductivity gap of fully
stoichiometric films greatly depends on the domain size, which increases
gradually with increasing film thickness, (2) that the broadness of the
transition scales with the width of the domain size distribution, and (3) that
the hysteresis width is affected strongly by the presence of antiphase
boundaries. Films grown on MgO (001) substrates showed the highest and sharpest
transitions, with a 200 nm film having a T of 122K, which is close to the
bulk value. Films grown on substrates with large lattice constant mismatch
revealed very broad transitions, and yet, all films show a transition with a
hysteresis behavior, indicating that the transition is still first order rather
than higher order.Comment: 9 pages, 12 figure
Magnetically induced Ferroelectricity in BiCuO
The tetragonal copper oxide BiCuO has an unusual crystal structure
with a three-dimensional network of well separated CuO plaquettes. This
material was recently predicted to host electronic excitations with an
unconventional spectrum and the spin structure of its magnetically ordered
state appearing at T 43 K remains controversial. Here we present the
results of detailed studies of specific heat, magnetic and dielectric
properties of BiCuO single crystals grown by the floating zone
technique, combined with the polarized neutron scattering and high-resolution
X-ray measurements. Our polarized neutron scattering data show Cu spins are
parallel to the plane. Below the onset of the long range antiferromagnetic
ordering we observe an electric polarization induced by an applied magnetic
field, which indicates inversion symmetry breaking by the ordered state of Cu
spins. For the magnetic field applied perpendicular to the tetragonal axis, the
spin-induced ferroelectricity is explained in terms of the linear
magnetoelectric effect that occurs in a metastable magnetic state. A relatively
small electric polarization induced by the field parallel to the tetragonal
axis may indicate a more complex magnetic ordering in BiCuO
Local Fiscal Adjustments from Depopulation: Evidence from the Post–Cold War Defense Contraction
In this paper, we estimate the long-term causal effect of population losses on local government revenue, expenditure, and debt by exploiting a quasi-exogenous change that reduced the number of US military personnel by about 40 percent between the late 1980s and 2000. Aggregating across governmental units within commuting zones, we find that real per capita total revenues and expenditures remained unchanged for remaining citizens. At the same time, however, we note several important compositional effects. First, local governments appear to have offset reductions in state intergovernmental aid by increasing property tax revenues. Second, they significantly shifted the composition of expenditures by making disproportionately large cuts in capital spending, including cuts in K–12 education, to maintain levels for current operations. Third, localities increased their long-term nonguaranteed debt to finance investments not covered by general capital outlays. Taken together, these actions run the risk of hindering a region’s relative competitiveness in the long term
Control of multiferroic domains by external electric fields in TbMnO3
The control of multiferroic domains through external electric fields has been
studied by dielectric measurements and by polarized neutron diffraction on
single-crystalline TbMnO. Full hysteresis cycles were recorded by varying
an external field of the order of several kV/mm and by recording the chiral
magnetic scattering as well as the charge in a sample capacitor. Both methods
yield comparable coercive fields that increase upon cooling.Comment: 12 pages, 6 figure
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