331 research outputs found
Ground State of the Easy-Axis Rare-Earth Kagom\'e Langasite PrGaSiO
We report muon spin relaxation (SR) and Ga nuclear quadrupolar
resonance (NQR) local-probe investigations of the kagom\'e compound
PrGaSiO. Small quasi-static random internal fields develop below
40 K and persist down to our base temperature of 21 mK. They originate from
hyperfine-enhanced Pr nuclear magnetism which requires a non-magnetic
Pr crystal-field (CF) ground state. Besides, we observe a broad maximum
of the relaxation rate at K which we attribute to the population of
the first excited magnetic CF level. Our results yield a Van-Vleck paramagnet
picture, at variance with the formerly proposed spin-liquid ground state.Comment: minor change
Persistent spin dynamics intrinsic to amplitude-modulated long-range magnetic order
An incommensurate elliptical helical magnetic structure in the frustrated
coupled-spin-chain system FeTe2O5Br is surprisingly found to persist down to
53(3) mK (T/T_N ~ 1/200), according to neutron scattering and muon spin
relaxation. In this state, finite spin fluctuations at T -> 0 are evidenced by
muon depolarization, which is in agreement with specific-heat data indicating
the presence of both gapless and gapped excitations. We thus show that the
amplitude-modulated magnetic order intrinsically accommodates contradictory
persistent spin dynamics and long-range order and can serve as a model
structure to investigate their coexistence.Comment: 5 pages + supplementar
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.
Recovering Metallicity in A4C60: The Case of Monomeric Li4C60
The restoration of metallicity in the high-temperature, cubic phase of Li4C60
represents a remarkable feature for a member of the A4C60 family (A = alkali
metal), invariably found to be insulators. Structural and resonance technique
investigations on Li4C60 at T > 600 K, show that its fcc structure is
associated with a complete (4e) charge transfer to C60 and a sparsely populated
Fermi level. These findings not only emphasize the crucial role played by
lattice symmetry in fulleride transport properties, but also re-dimension the
role of Jahn-Teller effects in band structure determination. Moreover, they
suggest the present system as a potential precursor to a new class of
superconducting fullerides.Comment: 4 pages, 3 figure
Evolution of magnetic and crystal structures in the multiferroic FeTe2O5Br
Neutron diffraction and nuclear quadrupole resonance (NQR) measurements were
employed to investigate magnetic order in the non-ferroelectric phase preceding
the low-temperature multiferroic state in FeTe2O5Br. Refnement of the neutron
diffraction data and simulations of 79,81Br NQR spectra reveal that the
incommensurate magnetic ordering in the non-ferroelectric state comprises
amplitude-modulated magnetic moments, similarly as in the multiferroic state.
The two ordered states differ in the orientation of the magnetic moments and
phase shifts between modulation waves. Surprisingly, all symmetry restrictions
for the electric polarization are absent in both states. The different
ferroelectric responses of the two states are thus argued to arise from the
differences in the phase shifts between certain modulation waves, which cancel
out in the non-ferrolectric state.Comment: 9 pages, 8 figures including appendix, published in PR
Spin-stripe phase in a frustrated zigzag spin-1/2 chain
Motifs of periodic modulations are encountered in a variety of natural
systems, where at least two rival states are present. In strongly correlated
electron systems such behaviour has typically been associated with competition
between short- and long-range interactions, e.g., between exchange and
dipole-dipole interactions in the case of ferromagnetic thin films. Here we
show that spin-stripe textures may develop also in antiferromagnets, where
long-range dipole-dipole magnetic interactions are absent. A comprehensive
analysis of magnetic susceptibility, high-field magnetization, specific heat,
and neutron diffraction measurements unveils -TeVO as a nearly
perfect realization of a frustrated (zigzag) ferromagnetic spin-1/2 chain.
Strikingly, a narrow spin stripe phase develops at elevated magnetic fields due
to weak frustrated short-range interchain exchange interactions possibly
assisted by the symmetry allowed electric polarization. This concept provides
an alternative route for the stripe formation in strongly correlated electron
systems and may help understanding other widespread, yet still elusive,
stripe-related phenomena.Comment: accapted in Nature Communication
Electron Spin Resonance of SrCu2(BO3)2 at High Magnetic Field
We calculate the electron spin resonance (ESR) spectra of the
quasi-two-dimensional dimer spin liquid SrCu2(BO3)2 as a function of magnetic
field B. Using the standard Lanczos method, we solve a Shastry-Sutherland
Hamiltonian with additional Dzyaloshinsky-Moriya (DM) terms which are crucial
to explain different qualitative aspects of the ESR spectra. In particular, a
nearest-neighbor DM interaction with a non-zero D_z component is required to
explain the low frequency ESR lines for B || c. This suggests that crystal
symmetry is lowered at low temperatures due to a structural phase transition.Comment: 4 pages, 4 b&w figure
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