28 research outputs found
Phonon-modulated magnetic interactions and spin Tomonaga-Luttinger liquid in the p-orbital antiferromagnet CsO2
The magnetic response of antiferromagnetic CsO2, coming from the p-orbital
S=1/2 spins of anionic O2- molecules, is followed by 133Cs nuclear magnetic
resonance across the structural phase transition occuring at Ts1=61 K on
cooling. Above Ts1, where spins form a square magnetic lattice, we observe a
huge, nonmonotonic temperature dependence of the exchange coupling originating
from thermal librations of O2- molecules. Below Ts1, where antiferromagnetic
spin chains are formed as a result of p-orbital ordering, we observe a spin
Tomonaga-Luttinger-liquid behavior of spin dynamics. These two interesting
phenomena, which provide rare simple manifestations of the coupling between
spin, lattice and orbital degrees of freedom, establish CsO2 as a model system
for molecular solids.Comment: 9 pages, 5 figures (with Supplemental Material), to appear in
Physical Review Letter
One-dimensional quantum antiferromagnetism in the orbital CsO compound revealed by electron paramagnetic resonance
Recently it was proposed that the orbital ordering of molecular
orbitals in the superoxide CsO compound leads to the formation of spin-1/2
chains below the structural phase transition occuring at ~K on
cooling. Here we report a detailed X-band electron paramagnetic resonance (EPR)
study of this phase in CsO powder. The EPR signal appears as a broad line
below , which is replaced by the antiferromagnetic resonance below
the N\'{e}el temperature ~K. The temperature dependence of the
EPR linewidth between and agrees with the
predictions for the one-dimensional Heisenberg antiferromagnetic chain of
spins in the presence of symmetric anisotropic exchange interaction.
Complementary analysis of the EPR lineshape, linewidth and the signal intensity
within the Tomonaga-Luttinger liquid (TLL) framework allows for a determination
of the TLL exponent . Present EPR data thus fully comply with the
quantum antiferromagnetic state of spin-1/2 chains in the orbitally ordered
phase of CsO, which is, therefore, a unique orbital system where such a
state could be studied.Comment: 6 pages, 3 figure
Neutron diffraction investigation of the H-T phase diagram above the longitudinal incommensurate phase of BaCo2V2O8
The quasi-one-dimensional antiferromagnetic Ising-like compound BaCo2V2O8 has
been shown to be describable by the Tomonaga-Luttinger liquid theory in its
gapless phase induced by a magnetic field applied along the Ising axis. Above
3.9 T, this leads to an exotic field-induced low-temperature magnetic order,
made of a longitudinal incommensurate spin-density wave, stabilized by weak
interchain interactions. By single-crystal neutron diffraction we explore the
destabilization of this phase at a higher magnetic field. We evidence a
transition at around 8.5 T towards a more conventional magnetic structure with
antiferromagnetic components in the plane perpendicular to the magnetic field.
The phase diagram boundaries and the nature of this second field-induced phase
are discussed with respect to previous results obtained by means of nuclear
magnetic resonance and electron spin resonance, and in the framework of the
simple model based on the Tomonaga-Luttinger liquid theory, which obviously has
to be refined in this complex system.Comment: 7 pages, 5 figure
Symmetric and antisymmetric exchange anisotropies in quasi-one-dimensional CuSeO as revealed by ESR
We present an electron spin resonance (ESR) study of single-crystalline spin
chain-system CuSeO in the frequency range between 9 GHz and 450 GHz. In
a wide temperature range above the N\'{e}el temperature K we observe
strong and anisotropic frequency dependence of a resonance linewidth. Although
sizeable interchain interaction ( is the intrachain
interaction) is present in this system, the ESR results agree well with the
Oshikawa-Affleck theory for one-dimensional Heisenberg antiferromagnet.
This theory is used to extract the anisotropies present in CuSeO. We
find that the symmetric anisotropic exchange and the
antisymmetric Dzyaloshinskii-Moriya (DM) interaction are
very similar in size in this system. Staggered-field susceptibility induced by
the presence of the DM interaction is witnessed in the macroscopic
susceptibility anisotropy.Comment: 8 pages, 7 figures, 2 tables, published in Phys. Rev.
Antiferromagnetic fluctuations in the normal state of LiFeAs
We present a detailed study of 75As NMR Knight shift and spin-lattice
relaxation rate in the normal state of stoichiometric polycrystalline LiFeAs.
Our analysis of the Korringa relation suggests that LiFeAs exhibits strong
antiferromagnetic fluctuations, if transferred hyperfine coupling is a dominant
interaction between 75As nuclei and Fe electronic spins, whereas for an on-site
hyperfine coupling scenario, these are weaker, but still present to account for
our experimental observations. Density-functional calculations of electric
field gradient correctly reproduce the experimental values for both 75As and
7Li sites.Comment: 5 pages, 3 figures, thoroughly revised version with refined
experimental data, accepted for publication as a Rapid Communication in
Physical Review B
Giant magnetic-field dependence of the coupling between spin Tomonaga-Luttinger liquids in BaCo2V2O8
We use nuclear magnetic resonance to map the complete low-temperature phase
diagram of the antiferromagnetic Ising-like spin-chain system BaCo2V2O8 as a
function of the magnetic field applied along the chains. In contrast to the
predicted crossover from the longitudinal incommensurate phase to the
transverse antiferromagnetic phase, we find a sequence of three magnetically
ordered phases between the critical fields 3.8 T and 22.8 T. Their origin is
traced to the giant magnetic-field dependence of the total effective coupling
between spin chains, extracted to vary by a factor of 24. We explain this novel
phenomenon as emerging from the combination of nontrivially coupled spin chains
and incommensurate spin fluctuations in the chains treated as
Tomonaga-Luttinger liquids.Comment: 6 pages, 3 figure