444 research outputs found
Spin Dynamical Properties of the Layered Perovskite La1.2Sr1.8Mn2O7
Inelastic neutron-scattering measurements were performed on a single crystal
of the layered colossal magnetoresistance (CMR) material La1.2Sr1.8Mn2O7 (Tc ~
120K). We found that the spin wave dispersion is almost perfectly
two-dimensional with the in-plane spin stiffness constant D ~ 151meVA. The
value is similar to that of similarly doped La1-xSrxMnO3 though its Tc is three
times higher, indicating a large renormalization due to low dimensionality.
There exist two branches due to a coupling between layers within a
double-layer. The out-of-plane coupling is about 30% of the in-plane coupling
though the Mn-O bond lengths are similar.Comment: 3 pages, 3 figures J. Phys. Chem. Solids in pres
Interplay of the CE-type charge ordering and the A-type spin ordering in a half-doped bilayer manganite La{1}Sr{2}Mn{2}O{7}
We demonstrate that the half-doped bilayer manganite La_{1}Sr_{2}Mn_{2}O_{7}
exhibits CE-type charge-ordered and spin-ordered states below K and below K, respectively. However, the volume
fraction of the CE-type ordering is relatively small, and the system is
dominated by the A-type spin ordering. The coexistence of the two types of
ordering is essential to understand its transport properties, and we argue that
it can be viewed as an effective phase separation between the metallic
orbital ordering and the charge-localized
orbital ordering.Comment: 5 pages, 4 figures, submitted to Phys. Rev.
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
Large thermal Hall coefficient in bismuth
We present a systematical study of thermal Hall effect on a bismuth single
crystal by measuring resistivity, Hall coefficient, and thermal conductivity
under magnetic field, which shows a large thermal Hall coefficient comparable
to the largest one in a semiconductor HgSe. We discuss that this is mainly due
to a large mobility and a low thermal conductivity comparing theoretical
calculations, which will give a route for controlling heat current in
electronic devices.Comment: 4pages, 3 figure
Spin and orbital ordering in double-layered manganites
We study theoretically the phase diagram of the double-layered perovskite
manganites taking into account the orbital degeneracy, the strong Coulombic
repulsion, and the coupling with the lattice deformation. Observed spin
structural changes as the increased doping are explained in terms of the
orbital ordering and the bond-length dependence of the hopping integral along
-axis. Temperature dependence of the neutron diffraction peak corresponding
to the canting structure is also explained. Comparison with the 3D cubic system
is made.Comment: 7 figure
Spin dynamical properties and orbital states of the layered perovskite La_2-2x_Sr_1+2x_Mn_2_O_7 (0.3 <= x < 0.5)
Low-temperature spin dynamics of the double-layered perovskite
La_2-2x_Sr_1+2x_Mn_2_O_7 (LSMO327) was systematically studied in a wide hole
concentration range (0.3 <= x < 0.5). The spin-wave dispersion, which is almost
perfectly 2D, has two branches due to a coupling between layers within a
double-layer. Each branch exhibits a characteristic intensity oscillation along
the out-of-plane direction. We found that the in-plane spin stiffness constant
and the gap between the two branches strongly depend on x. By fitting to
calculated dispersion relations and cross sections assuming Heisenberg models,
we have obtained the in-plane (J_para), intra-bilayer (J_perp) and
inter-bilayer (J') exchange interactions at each x. At x=0.30, J_para=-4meV and
J_perp=-5meV, namely almost isotropic and ferromagnetic. Upon increasing x,
J_perp rapidly approaches zero while |J_para| increases slightly, indicating an
enhancement of the planar magnetic anisotropy. At x=0.48, J_para reaches -9meV,
while J_perp turns to +1meV indicating an antiferromagnetic interaction. Such a
drastic change of the exchange interactions can be ascribed to the change of
the relative stability of the d_x^2-y^2 and d_3z^2-r^2 orbital states upon
doping. However, a simple linear combination of the two states results in an
orbital state with an orthorhombic symmetry, which is inconsistent with the
tetragonal symmetry of the crystal structure. We thus propose that an ``orbital
liquid'' state realizes in LSMO327, where the charge distribution symmetry is
kept tetragonal around each Mn site.Comment: 10 pages including 7 figure
Observation of anomalous single-magnon scattering in half-metallic ferromagnets by chemical pressure control
Temperature variation of resistivity and specific heat have been measured for
prototypical half-metallic ferromagnets,
R_0.6Sr_0.4MnO_3, with controlling the one-electron bandwidth W. We have
found variation of the temperature scalings in the resistivity from
T^2 (R = La, and Nd) to T^3 (R = Sm), and have interpreted the $T^3-law in
terms of the anomalous single-magnon scattering (AMS) process in the
half-metallic system.Comment: To appear in Phys. Rev. Lett., 3 pages + 4 EPS figure
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