96 research outputs found
Muon-spin-rotation study of the magnetic structure in the tetragonal antiferromagnetic state of weakly underdoped BaKFeAs
With muon spin rotation (SR) we studied the transition between the
orthorhombic antiferromagnetic (o-AF) and the tetragonal antiferromagnetic
(t-AF) states of a weakly underdoped BaKFeAs
single crystal. We observed some characteristic changes of the magnitude and
the orientation of the magnetic field at the muon site which, due to the fairly
high point symmetry of the latter, allow us to identify the magnetic structure
of the t-AF state. It is the so-called, inhomogeneous double-
magnetic structure with -axis oriented moments which has a vanishing
magnetic moment on half of the Fe sites.Comment: 5 pages, 4 figures. Supplementary Material: 8 figure
Dynamical lattice instability versus spin liquid state in a frustrated spin chain system
The low-dimensional s=1/2 compound (NO)[Cu(NO3)3] has recently been suggested
to follow the Nersesyan-Tsvelik model of coupled spin chains. Such a system
shows unbound spinon excitations and a resonating valence bond ground state due
spin frustration. Our Raman scattering study demonstrates phonon anomalies as
well as the suppression of a broad magnetic scattering continuum for
temperatures below a characteristic temperature, T<T*=100K. We interpret these
effects as evidence for a dynamical interplay of spin and lattice degrees of
freedom that might lead to a further transition into a dimerized or
structurally distorted phase at lower temperatures.Comment: 5 pages, 6 figure
Orbiton-mediated multi-phonon scattering in LaSrMnO
We report on Raman scattering measurements of single crystalline
LaSrMnO (=0, 0.06, 0.09 and 0.125), focusing on the high
frequency regime. We observe multi-phonon scattering processes up to
fourth-order which show distinct features: (i) anomalies in peak energy and its
relative intensity and (ii) a pronounced temperature-, polarization-, and
doping-dependence. These features suggest a mixed orbiton-phonon nature of the
observed multi-phonon Raman spectra.Comment: 6pages, 6figures, submitted to PR
Low temperature mixed spin state of Co3+ in LaCoO3 evidenced from Jahn-Teller lattice distortions
One- and multi-phonon excitations of the single crystalline LaCoO3 were
studied using Raman spectroscopy in the temperature region of 5 K - 300 K.
First-order Raman spectra show a larger number of phonon modes than allowed for
the rhombohedral structure. Additional phonon modes are interpreted in terms of
activated modes due to lattice distortions, arising from the Jahn-Teller (JT)
activity of the intermediate-spin (IS) state of Co3+ ions. In particular, the
608-cm-1 stretching-type mode shows anomalous behavior in peak energy and
scattering intensity as a function of temperature. The anomalous temperature
dependence of the second-order phonon excitations spectra is in accordance with
the Franck-Condon mechanism that is characteristic for a JT orbital order.Comment: 11 pages, 9 figures, to be published in J. Low. Temp. Physic
Microscopic Evidence of Spin State Order and Spin State Phase Separation in Layered Cobaltites RBaCo2O5.5 with R=Y, Tb, Dy, and Ho
We report muon spin relaxation measurements on the magnetic structures of
RBaCo_2O_5.5 with R=Y, Tb, Dy, and Ho. Three different phases, one
ferrimagnetic and two antiferromagnetic, are identified below 300 K. They
consist of different ordered spin state arrangements of high-, intermediate-,
and low-spin Co^3+ of CoO_6 octahedra. Phase separation into well separated
regions with different spin state order is observed in the antiferromagnetic
phases. The unusual strongly anisotropic magnetoresistance and its onset at the
FM-AFM phase boundary is explained.Comment: 4 pages, accepted for publication in Phys. Rev. Let
Evidence for local lattice distortions in giant magnetocapacitive CdCr2S4
Raman scattering experiments on CdCr2S4 single crystals show pronounced
anomalies in intensity and frequency of optical phonon modes with an onset
temperature T*=130 K that coincides with the regime of giant magnetocapacitive
effects. A loss of inversion symmetry and Cr off-centering are deduced from the
observation of longitudinal optical and formerly infrared active modes for
T<T_c=84 K. The intensity anomalies are attributed to the enhanced electronic
polarizability of displacements that modulate the Cr-S distance and respective
hybridization. Photo doping leads to an annihilation of the symmetry reduction.
Our scenario of multiferroic effects is based on the near degeneracy of polar
and nonpolar modes and the additional low energy scale due to hybridization.Comment: 4 pages, 6 figure
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