249 research outputs found
The magnetoresistance tensor of La(0.8)Sr(0.2)MnO(3)
We measure the temperature dependence of the anisotropic magnetoresistance
(AMR) and the planar Hall effect (PHE) in c-axis oriented epitaxial thin films
of La(0.8)Sr(0.2)MnO(3), for different current directions relative to the
crystal axes, and show that both AMR and PHE depend strongly on current
orientation. We determine a magnetoresistance tensor, extracted to 4th order,
which reflects the crystal symmetry and provides a comprehensive description of
the data. We extend the applicability of the extracted tensor by determining
the bi-axial magnetocrystalline anisotropy in our samples
Unraveling Orbital Correlations via Magnetic Resonant Inelastic X-ray Scattering
Although orbital degrees of freedom are a factor of fundamental importance in
strongly correlated transition metal compounds, orbital correlations and
dynamics remain very difficult to access, in particular by neutron scattering.
Via a direct calculation of scattering amplitudes we show that instead magnetic
resonant inelastic x-ray scattering (RIXS) does reveal orbital correlations. In
contrast to neutron scattering, the intensity of the magnetic excitations in
RIXS depends very sensitively on both the symmetry of the orbitals that spins
occupy, and on photon polarizations. We show in detail how this effect allows
magnetic RIXS to distinguish between alternating orbital ordered and
ferro-orbital (or orbital liquid) states.Comment: 7 pages, 4 figures. Supplemental material adde
Optical control of magnetization of micron-size domains in antiferromagnetic NiO single crystals
We propose Raman-induced collinear difference-frequency generation (DFG) as a
method to manipulate dynamical magnetization. When a fundamental beam
propagates along a threefold rotational axis, this coherent second-order
optical process is permitted by angular momentum conservation through the
rotational analogue of the Umklapp process. As a demonstration, we
experimentally obtained polarization properties of collinear magnetic DFG along
a [111] axis of a single crystal of antiferromagnetic NiO with micro
multidomain structure, which excellently agreed with the theoretical
prediction.Comment: 11 pages, 3 figures, submitted to Physical Review Letter
Novel Field-Induced Phases in HoMnO3 at Low Temperatures
The novel field-induced re-entrant phase in multiferroic hexagonal HoMnO3 is
investigated to lower temperatures by dc magnetization, ac susceptibility, and
specific heat measurements at various magnetic fields. Two new phases have been
unambiguously identified below the Neel transition temperature, TN=76 K, for
magnetic fields up to 50 kOe. The existence of an intermediate phase between
the P[6]_3[c]m and P[6]_3c[m] magnetic structures (previously predicted from
dielectric measurements) was confirmed and the magnetic properties of this
phase have been investigated. At low temperatures (T<5 K) a dome shaped phase
boundary characterized by a magnetization jump and a narrow heat capacity peak
was detected between the magnetic fields of 5 kOe and 18 kOe. The transition
across this phase boundary is of first order and the magnetization and entropy
jumps obey the magnetic analogue of the Clausius-Clapeyron relation. Four of
the five low-temperature phases coexist at a tetracritical point at 2 K and 18
kOe. The complex magnetic phase diagram so derived provides an informative
basis for unraveling the underlying driving forces for the occurrence of the
various phases and the coupling between the different orders.Comment: 14 pages, 14 figure
Symmetry Analysis of Multiferroic Co_3TeO_6
A phenomenological explanation of the magnetoelectric behavior of Co_3TeO_6
is developed. We explain the second harmonic generation data and the magnetic
field induced spontaneous polarization in the magnetically ordered phase below
20K.Comment: Phys rev B Rapids, to appea
A Field-Induced Re-Entrant Novel Phase and A Ferroelectric-Magnetic Order Coupling in HoMnO3
A re-entrant novel phase has been observed in the hexagonal ferroelectric
HoMnO3 in the presence of magnetic fields, in the temperature ranges defined by
the plateau of the dielectric constant anomaly. The dielectric plateau evolves
with fields from a narrow sharp dielectric peak at the Mn-spin rotation
transition at 32.8 K in zero magnetic field. Such a field-induced dielectric
plateau anomaly appears both in the temperature sweep at a constant field and
in the field sweep at a constant temperature without detectable hysteresis.
This is attributed to the indirect coupling between the ferroelectric and
antiferromagnetic orders, arising from an antiferromagnetic domain wall effect,
where the magnetic order parameter of the Mn subsystem has to change sign
across the ferroelectric domain wall in the compound, that influences the
ferroelectric domains via a local magnetostrictive effect
Polar Antiferromagnets Produced with Orbital-Order
Polar magnetic states are realized in pseudocubic manganite thin films
fabricated on high-index substrates, in which a Jahn-Teller (JT) distortion
remains an active variable. Several types of orbital-orders were found to
develop large optical second harmonic generation, signaling
broken-inversion-symmetry distinct from their bulk forms and films on (100)
substrates. The observed symmetry-lifting and first-principles calculation both
indicate that the modified JT q2 mode drives Mn-site off-centering upon orbital
order, leading to the possible cooperation of "Mn-site polarization" and
magnetism.Comment: 5 pages, 4 figure
Weak Ferromagnetism Accompanying Loop current order in Underdoped Cuprates
We discuss the necessary symmetry conditions and the different ways in which
they can be physically realized for the occurrence of ferromagnetism
accompanying the loop current orbital magnetic order observed by polarized
neutron-diffraction experiments or indeed any other conceivable principal order
in the under-doped phase of cuprates. We contrast the Kerr effect experiments
in single crystals observing ferromagnetism with the direct magnetization
measurements in large powder samples, which do not observe it. We also suggest
experiments to resolve the differences among the experiments, all of which we
believe to be correct.Comment: 4 page
Low temperature dielectric anomalies in HoMnO_3: The complex phase diagram
The dielectric constant of multiferroic hexagonal HoMnO_3 exhibits an
unprecedented diversity of anomalies at low temperatures (1.8 K< T <10 K) and
under external magnetic fields related to magnetic phase transitions in the
coupled system of Ho moments, Mn spins, and ferroelectric polarization. The
derived phase diagram is far more complex than previously assumed including
reentrant phases, phase transitions with distinct thermal and field hysteresis,
as well as several multicritical points. Magnetoelastic interactions introduce
lattice anomalies at the magnetic phase transitions. The re-evaluation of the
T-H phase diagram of HoMnO_3 is demanded.Comment: 12 pages, 3 figure
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