1,231 research outputs found

### Magnetic incommensurability in $p$-type cuprate perovskites

For the superconducting phase with a d-wave order parameter and zero
temperature the magnetic susceptibility of the t-J model is calculated using
the Mori projection operator technique. Conditions for the appearance of an
incommensurate magnetic response below the resonance frequency are identified.
A fast decay of the tails of the hole coherent peaks and a weak intensity of
the hole incoherent continuum near the Fermi level are enough to produce an
incommensurate response using different hole dispersions established for
$p$-type cuprates, in which such response was observed. In this case, the
nesting of the itinerant-electron theory or the charge modulation of the stripe
theory is unnecessary for the incommensurability. The theory reproduces the
hourglass dispersion of the susceptibility maxima with their location in the
momentum space similar to that observed experimentally. The upper branch of the
dispersion stems from the excitations of localized spins, while the lower one
is due to the incommensurate maxima of their damping. The narrow and intensive
resonance peak arises if the frequency of these excitations at the
antiferromagnetic momentum lies below the edge of the two-fermion continuum;
otherwise the maximum is broad and less intensive.Comment: 22 pages, 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

### Pressure-tuned First-order Phase Transition and Accompanying Resistivity Anomaly in CeZn_{1-\delta}Sb_{2}

The Kondo lattice system CeZn_{0.66}Sb_{2} is studied by the electrical
resistivity and ac magnetic susceptibility measurements at several pressures.
At P=0 kbar, ferromagnetic and antiferromagnetic transitions appear at 3.6 and
0.8 K, respectively. The electrical resistivity at T_N dramatically changes
from the Fisher-Langer type (ferromagnetic like) to the Suzaki-Mori type near
17 kbar, i.e., from a positive divergence to a negative divergence in the
temperature derivative of the resistivity. The pressure-induced SM type
anomaly, which shows thermal hysteresis, is easily suppressed by small magnetic
field (1.9 kOe for 19.8 kbar), indicating a weakly first-order nature of the
transition. By subtracting a low-pressure data set, we directly compare the
resistivity anomaly with the SM theory without any assumption on backgrounds,
where the negative divergence in d\rho/dT is ascribed to enhanced critical
fluctuations in the presence of superzone gaps.Comment: 5 pages, 4 figures; journal-ref adde

### Extended skyrmion lattice scattering and long-time memory in the chiral magnet Fe$_{1-x}$Co$_x$Si

Small angle neutron scattering measurements on a bulk single crystal of the
doped chiral magnet Fe$_{1-x}$Co$_x$Si with $x$=0.3 reveal a pronounced effect
of the magnetic history and cooling rates on the magnetic phase diagram. The
extracted phase diagrams are qualitatively different for zero and field cooling
and reveal a metastable skyrmion lattice phase outside the A-phase for the
latter case. These thermodynamically metastable skyrmion lattice correlations
coexist with the conical phase and can be enhanced by increasing the cooling
rate. They appear in a wide region of the phase diagram at temperatures below
the $A$-phase but also at fields considerably smaller or higher than the fields
required to stabilize the A-phase

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