41 research outputs found
High-Pressure Suppression of Long Range Magnetic Order in the Triangular Lattice Antiferromagnet CuFeO2
We succeeded in observing pressure-suppressed magnetic long range ordering
(LRO) in the triangular lattice antiferromagnet CuFeO, using neutron
diffraction experiments under an isotropic pressure. The magnetic LRO of the
four-sublattice ground state under ambient pressure in CuFeO almost
disappears at the high pressure of 7.9 GPa, and is replaced by an
incommensurate order with temperature-independent wave number of (0.192 0.192
1.5). The incommensurate wave number observed at 7.9 GPa corresponds to that
observed just above the temperature at which lattice distortion and magnetic
LRO simultaneously occur under ambient pressure. Therefore, the long-range
magnetic ordering disappears because the high pressure suppressed the lattice
distortion that otherwise relieves spin frustration and leads the spin system
to LRO.Comment: 4 pages, 3 figure
Magnons and electromagnons in a spin-lattice-coupled frustrated magnet CuFeO2 as seen via inelastic neutron scattering
We have investigated spin-wave excitations in a four-sublattice (4SL)
magnetic ground state of a frustrated magnet CuFeO2, in which `electromagnon'
(electric-field-active magnon) excitation has been discovered by recent
terahertz time-domain spectroscopy [Seki et al. Phys. Rev. Lett. 105 097207
(2010)]. In previous study, we have identified two spin-wave branches in the
4SL phase by means of inelastic neutron scattering measurements under applied
uniaxial pressure. [T. Nakajima et al. J. Phys. Soc. Jpn. 80 014714 (2011) ] In
the present study, we have performed high-energy-resolution inelastic neutron
scattering measurements in the 4SL phase, resolving fine structures of the
lower-energy spin-wave branch near the zone center. Taking account of the
spin-driven lattice distortions in the 4SL phase, we have developed a model
Hamiltonian to describe the spin-wave excitations. The determined Hamiltonian
parameters have successfully reproduced the spin-wave dispersion relations and
intensity maps obtained in the inelastic neutron scattering measurements. The
results of the spin-wave analysis have also revealed physical pictures of the
magnon and electromagnon modes in the 4SL phase, suggesting that collinear and
noncollinear characters of the two spin-wave modes are the keys to understand
the dynamical coupling between the spins and electric dipole moments in this
system.Comment: 8 pages, 6 figure
Identification of microscopic spin-polarization coupling in the ferroelectric phase of a magnetoelectric multiferroic CuFe1-xAlxO2
We have performed synchrotron radiation X-ray and neutron diffraction
measurements on magnetoelectric multiferroic CuFe1-xAlxO2 (x=0.0155), which has
a proper helical magnetic structure with incommensurate propagation wave vector
in the ferroelectric phase. The present measurements revealed that the
ferroelectric phase is accompanied by lattice modulation with a wave number 2q,
where q is the magnetic modulation wave number. We have calculated the Fourier
spectrum of the spatial modulations in the local electric polarization using a
microscopic model proposed by Arima [T. Arima, J. Phys. Soc. Jpn. 76, 073702
(2007)]. Comparing the experimental results with the calculation results, we
found that the origin of the 2q-lattice modulation is not conventional
magnetostriction but the variation in the metal-ligand hybridization between
the magnetic Fe^3+ ions and ligand O^2- ions. Combining the present results
with the results of a previous polarized neutron diffraction study [Nakajima et
al., Phys. Rev. B 77 052401 (2008)], we conclude that the microscopic origin of
the ferroelectricity in CuFe1-xAlxO2 is the variation in the metal-ligand
hybridization with spin-orbit coupling.Comment: 11 pages, 9 figures, to be published in Phys. Rev.