870 research outputs found
Novel stripe-type charge ordering in the metallic A-type antiferromagnet Pr{0.5}Sr{0.5}MnO{3}
We demonstrate that an A-type antiferromagnetic (AFM) state of
Pr{0.5}Sr{0.5}MnO{3} exhibits a novel charge ordering which governs the
transport property. This charge ordering is stripe-like, being characterized by
a wave vector q ~ (0,0,0.3) with very anisotropic correlation parallel and
perpendicular to the stripe direction. This charge ordering is specific to the
manganites with relatively wide one-electron band width (W) which often exhibit
a metallic A-type AFM state, and should be strictly distinguished from the
CE-type checkerboard-like charge ordering which is commonly observed in
manganites with narrower W such as La{1-x}Ca{x}MnO{3} and Pr{1-x}Ca{x}MnO{3}.Comment: REVTeX4, 5 pages, 4 figure
The Effect of - Magnetic Coupling in Multiferroic MnO Crystals
We have established detailed magnetoelectric phase diagrams of
(EuY)TbMnO () and
(Eu,Y)GdMnO (), whose average ionic radii of
-site (: rare earth) cations are equal to that of Tb, in order to
reveal the effect of rare earth 4 magnetic moments on the magnetoelectric
properties. In spite of the same -site ionic radii, the magnetoelectric
properties of the two systems are remarkably different from each other. A small
amount of Tb substitution on sites () totally destroys
ferroelectric polarization along the a axis (), and an increase in Tb
concentration stabilizes the phase. On the other hand, Gd substitution
() extinguishes the phase, and slightly suppresses the
phase. These results demonstrate that the magnetoelectric properties of
MnO strongly depend on the characteristics of the rare earth 4
moments.Comment: 10 pages, 5 figures Submitted to Journal of the Physical Society of
Japa
Magnetic Order and Dynamics in Stripe-Ordered La2-xSrxNiO4
We have studied magnetic correlations in several compositions of
stripe-ordered La2-xSrxNiO4. In this paper we show how polarized-neutron
scattering has helped uncover important features of the magnetic ordering and
spin dynamics. In particular, polarization analysis has enabled us (1) to
characterize a spin reorientation transition, (2) to identify anisotropy gaps
in the spin excitation spectrum, and (3) to investigate an anomalous dip in the
spin-wave intensity suggestive of coupling between collective spin and charge
excitations.Comment: 4 pages, 3 figs. Presented at PNSXM, Venice. To appear in Physica
Chemical potential shift and spectral weight transfer in PrCaMnO revealed by photoemission spectroscopy
We have studied the chemical potential shift and changes in the electronic
density of states near the Fermi level () as a function of carrier
concentration in PrCaMnO (PCMO, ) through
the measurements of photoemission spectra. The results showed that the chemical
potential shift was suppressed for x \agt 0.3, where the charge exchange
(CE)-type antiferromagnetic charge-ordered state appears at low temperatures.
We consider this observation to be related to charge self-organization such as
stripe formation on a microscopic scale in this composition range. Together
with the previous observation of monotonous chemical potential shift in
LaSrMnO, we conclude that the tendency toward the charge
self-organization increases with decreasing bandwidth. In the valence band,
spectral weight of the Mn 3 electrons in PCMO was transferred from
1 eV below to the region near with hole doping, leading to a
finite intensity at even in the paramagnetic insulating phase for x \agt
0.3, probably related with the tendency toward charge self-organization. The
finite intensity at in spite of the insulating transport behavior is
consistent with fluctuations involving ferromagnetic metallic states.Comment: 6 pages, 5 figure
Influence of Mg, Ag and Al substitutions on the magnetic excitations in the triangular-lattice antiferromagnet CuCrO2
Magnetic excitations in CuCrO, CuCrMgO,
CuAgCrO, and CuCrAlO have been
studied by powder inelastic neutron scattering to elucidate the element
substitution effects on the spin dynamics in the Heisenberg triangular-lattice
antiferromagnet CuCrO. The magnetic excitations in
CuCrMgO consist of a dispersive component and a flat
component. Though this feature is apparently similar to CuCrO, the energy
structure of the excitation spectrum shows some difference from that in
CuCrO. On the other hand, in CuAgCrO and
CuCrAlO the flat components are much reduced, the
low-energy parts of the excitation spectra become intense, and additional
low-energy diffusive spin fluctuations are induced. We argued the origins of
these changes in the magnetic excitations are ascribed to effects of the doped
holes or change of the dimensionality in the magnetic correlations.Comment: 7 pages, 5 figure
Charge and Orbital Ordering in Pr_{0.5} Ca_{0.5} MnO_3 Studied by ^{17}O NMR
The charge and orbital ordering in Pr_{0.5} Ca_{0.5} MnO_3 is studied for the
first time by ^{17}O NMR. This local probe is sensitive to spin, charge and
orbital correlations. Two transitions exist in this system: the charge and
orbital ordering at T_{CO} = 225 K and the antiferromagnetic (AF) transition at
T_N = 170 K. Both are clearly seen in the NMR spectra measured in a magnetic
field of 7T. Above T_{CO} there exists only one NMR line with a large isotropic
shift, whose temperature dependence is in accordance with the presence of
ferromagnetic (FM) correlations. This line splits into two parts below T_{CO},
which are attributed to different types of oxygen in the charge/orbital ordered
state. The interplay of FM and AF spin correlations of Mn ions in the charge
ordered state of Pr_{0.5} Ca_{0.5} MnO_3 is considered in terms of the hole
hopping motion that is slowed down with decreasing temperature. The developing
fine structure of the spectra evidences, that there still exist
charge-disordered regions at T_{CO} > T > T_N and that the static (t >
10^{-6}s) orbital order is established only on approaching T_N. The CE-type
magnetic correlations develop gradually below T_{CO}, so that at first the AF
correlations between checkerboard ab-layers appear, and only at lower
temperature - CE correlations within the ab-planes
Antiferro-quadrupole Ordering of CeB Studied by Resonant X-ray Scattering
Under zero magnetic field, a quadrupolar order parameter at q_Q=(1/2,1/2,1/2)
in a typical antiferro-quadrupole (AFQ) ordering compound CeB6 has been
observed for the first time by means of a resonant X-ray scattering (RXS) te\
chnique. The RXS is observed at the 2p->5d dipole transition energy of the Ce
L3-edge. Using this RXS technique to observe the pure order parameter of the
AFQ state, the magnetic phase diagram of Phase II is first determined.Comment: 7 pages, 4 figure
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