57 research outputs found
Magnetic Excitations in the Ground State of
We report an extensive study on the zero field ground state of a powder
sample of the pyrochlore . A sharp heat capacity anomaly
that labels a low temperature phase transition in this material is observed at
280 mK. Neutron diffraction shows that a \emph{quasi-collinear} ferromagnetic
order develops below with a magnetic moment of
. High resolution inelastic neutron scattering
measurements show, below the phase transition temperature, sharp gapped
low-lying magnetic excitations coexisting with a remnant quasielastic
contribution likely associated with persistent spin fluctuations. Moreover, a
broad inelastic continuum of excitations at meV is observed from the
lowest measured temperature up to at least 2.5 K. At 10 K, the continuum has
vanished and a broad quasielastic conventional paramagnetic scattering takes
place at the observed energy range. Finally, we show that the exchange
parameters obtained within the framework of linear spin-wave theory do not
accurately describe the observed zero field inelastic neutron scattering data.Comment: 11 pages, 9 figures, Phys. Rev. B. (accepted
Magnetic structures and magnetoelastic coupling of Fe-doped hexagonal manganites LuMn1-xFexO3 (0 < x < 0.3)
We have studied the crystal and magnetic structures of Fe-doped hexagonal
manganites LuMn1-xFexO3 (x = 0, 0.1, 0.2, and 0.3) by using bulk magnetization
and neutron powder diffraction methods. The samples crystalize consistently in
a hexagonal structure and maintain the space group P63cm from 2 to 300 K. The
N\'eel temperature TN increases continuously with increasing Fe-doping. In
contrast to a single {\Gamma}4 representation in LuMnO3, the magnetic ground
state of the Fe-doped samples can only be described with a spin configuration
described by a mixture of {\Gamma}3 (P63'cm') and {\Gamma}4 (P63'c'm)
representations, whose contributions have been quantitatively estimated. The
drastic effect of Fe-doping is highlighted by composition-dependent spin
reorientations. A phase diagram of the entire composition series is proposed
based on the present results and those reported in literature. Our result
demonstrates the importance of tailoring compositions in increasing magnetic
transition temperatures of multiferroic systems.Comment: 18 pages, 9 figure
Magnetic Lattice Dynamics of the Oxygen-Free FeAs Pnictides: How Sensitive are Phonons to Magnetic Ordering?
To shed light on the role of magnetism on the superconducting mechanism of
the oxygen-free FeAs pnictides, we investigate the effect of magnetic ordering
on phonon dynamics in the low-temperature orthorhombic parent compounds, which
present a spin-density wave. The study covers both the 122 (AFe2As2; A=Ca, Sr,
Ba) and 1111 (AFeAsF; A=Ca, Sr) phases. We extend our recent work on the Ca
(122 and 1111) and Ba (122) cases by treating computationally and
experimentally the 122 and 1111 Sr compounds. The effect of magnetic ordering
is investigated through detailed non-magnetic and magnetic lattice dynamical
calculations. The comparison of the experimental and calculated phonon spectra
shows that the magnetic interactions/ordering have to be included in order to
reproduce well the measured density of states. This highlights a
spin-correlated phonon behavior which is more pronounced than the apparently
weak electron-phonon coupling estimated in these materials. Furthermore, there
is no noticeable difference between phonon spectra of the 122 Ba and Sr,
whereas there are substantial differences when comparing these to CaFe2As2
originating from different aspects of structure and bonding
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