98 research outputs found
Circularly polarized resonant soft x-ray diffraction study of helical magnetism in hexaferrite
Magnetic spiral structures can exhibit ferroelectric moments as recently
demonstrated in various multiferroic materials. In such cases the helicity of
the magnetic spiral is directly correlated with the direction of the
ferroelectric moment and measurement of the helicity of magnetic structures is
of current interest. Soft x-ray resonant diffraction is particularly
advantageous because it combines element selectivity with a large magnetic
cross-section. We calculate the polarization dependence of the resonant
magnetic x-ray cross-section (electric dipole transition) for the basal plane
magnetic spiral in hexaferrite Ba0.8Sr1.2Zn2Fe12O22 and deduce its domain
population using circular polarized incident radiation. We demonstrate there is
a direct correlation between the diffracted radiation and the helicity of the
magnetic spiral.Comment: 4 pages, 4 figure
Covalency and vibronic couplings make a nonmagnetic j=3/2 ion magnetic
For 4d1 and 5d1 spin–orbit-coupled electron configurations, the notion of nonmagnetic j=3/2 quartet ground state discussed in classical textbooks is at odds with the observed variety of magnetic properties. Here we throw fresh light on the electronic structure of 4d1 and 5d1 ions in molybdenum- and osmium-based double-perovskite systems and reveal different kinds of on-site many-body physics in the two families of compounds: although the sizable magnetic moments and g-factors measured experimentally are due to both metal d–ligand p hybridisation and dynamic Jahn–Teller interactions for 4d electrons, it is essentially d−p covalency for the 5d1 configuration. These results highlight the subtle interplay of spin–orbit interactions, covalency and electron–lattice couplings as the major factor in deciding the nature of the magnetic ground states of 4d and 5d quantum materials. Cation charge imbalance in the double-perovskite structure is further shown to allow a fine tuning of the gap between the t2g and eg levels, an effect of much potential in the context of orbital engineering in oxide electronics
Commensurate lattice distortion in the layered titanium oxypnictides NaTiO ( As, Sb) determined by X-ray diffraction
We report single crystal X-ray diffraction measurements on
NaTiO ( = As, Sb) which reveal a charge superstructure that
appears below the density wave transitions previously observed in bulk data.
From symmetry-constrained structure refinements we establish that the
associated distortion mode can be described by two propagation vectors, and , with (Sb) or (As), and primarily involves in-plane displacements of the Ti atoms
perpendicular to the Ti--O bonds. The results provide direct evidence for
phonon-assisted charge density wave order in NaTiO and identify
a proximate ordered phase that could compete with superconductivity in doped
BaTiSbO
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Covalency and vibronic couplings make a nonmagnetic j=3/2 ion magnetic
For 4d1 and 5d1 spin–orbit-coupled electron configurations, the notion of nonmagnetic j=3/2 quartet ground state discussed in classical textbooks is at odds with the observed variety of magnetic properties. Here we throw fresh light on the electronic structure of 4d1 and 5d1 ions in molybdenum- and osmium-based double-perovskite systems and reveal different kinds of on-site many-body physics in the two families of compounds: although the sizable magnetic moments and g-factors measured experimentally are due to both metal d–ligand p hybridisation and dynamic Jahn–Teller interactions for 4d electrons, it is essentially d−p covalency for the 5d1 configuration. These results highlight the subtle interplay of spin–orbit interactions, covalency and electron–lattice couplings as the major factor in deciding the nature of the magnetic ground states of 4d and 5d quantum materials. Cation charge imbalance in the double-perovskite structure is further shown to allow a fine tuning of the gap between the t2g and eg levels, an effect of much potential in the context of orbital engineering in oxide electronics
The Final Chapter In The Saga Of YIG
The magnetic insulator Yttrium Iron Garnet can be grown with exceptional
quality, has a ferrimagnetic transition temperature of nearly 600 K, and is
used in microwave and spintronic devices that can operate at room temperature.
The most accurate prior measurements of the magnon spectrum date back nearly 40
years, but cover only 3 of the lowest energy modes out of 20 distinct magnon
branches. Here we have used time-of-flight inelastic neutron scattering to
measure the full magnon spectrum throughout the Brillouin zone. We find that
the existing model of the excitation spectrum, well known from an earlier work
titled "The Saga of YIG", fails to describe the optical magnon modes. Using a
very general spin Hamiltonian, we show that the magnetic interactions are both
longer-ranged and more complex than was previously understood. The results
provide the basis for accurate microscopic models of the finite temperature
magnetic properties of Yttrium Iron Garnet, necessary for next-generation
electronic devices.Comment: 10 pages, 3 figures, 4 supplementary figures, 1 table, 1
supplementary tabl
Chitosán más clorhexidina (Bexident®Post) en el control del dolor y la inflamación posoperatoria en implantologÃa oral: estudio piloto
Objetivos: Evaluación de la eficacia del chitosán más la clorhexidina en el control del dolor y la inflamación posoperatoria en cirugÃa implantológica oral. Material y métodos: Es un estudio clÃnico piloto prospectivo en pacientes a los que se les colocan implantes. A todos los pacientes se les pauta después de la cirugÃa Bexident®Post en gel, tres veces al dÃa durante siete dÃas. Se valora la inflamación, la apertura bucal, el nivel de dolor, el grado de cicatrización y la opinión sobre el producto. Resultados: Se han colocado 138 implantes en 54 pacientes. El 64% eran varones y la media de tiempo quirúrgico fue de 76 minutos. La inflamación y apertura bucal pre y postoperatoria no es significativa con una p= 0,000. Se han consumido 11 unidades analgésicas de media en los 7 dÃas del posoperatorio. El EVA ha sido de 3,0 (DS= 2,0) a las 6 horas, 2,0 (DS= 2,0) a las 24 horas, 2,02 (DS= 1,0) el segundo dÃa, 1,0 (DS= 1,0) el tercer y cuarto dÃa y 0,0 el quinto, sexto y séptimo dÃa. El grado de cicatrización es bueno en el 88,9% (48 pacientes); regular, en el 7,4% (4 pacientes) y malo, en el 3,7% (2 pacientes). 45 pacientes (83,3%) responden positivamente a todas las preguntas referentes al producto. Conclusiones: El producto se muestra fácil de usar, el sabor es adecuado y en este estudio la inflamación, el dolor y el consumo de medicamentos han sido mÃnimo
Coupling of magnetic order to planar Bi electrons in the anisotropic Dirac metals AMnBi2 (A = Sr, Ca)
We report powder and single crystal neutron diffraction measurements of the
magnetic order in AMnBi2 (A = Sr and Ca), two layered manganese pnictides with
anisotropic Dirac fermions on a Bi square net. Both materials are found to
order at TN approx 300 K in k = 0 antiferromagnetic structures, with ordered Mn
moments at T = 10 K of approximately 3.8 muB aligned along the c axis. The
magnetic structures are Neel-type within the Mn--Bi layers but the inter-layer
ordering is different, being antiferromagnetic in SrMnBi2 and ferromagnetic in
CaMnBi2. This allows a mean-field coupling of the magnetic order to Bi
electrons in CaMnBi2 but not in SrMnBi2. We find clear evidence that magnetic
order influences electrical transport. First principles calculations explain
the experimental observations and suggest that the mechanism for different
inter-layer ordering in the two compounds is the competition between the
anteiferromagnetic superexchange and ferromagnetic double exchange carried by
itinerant Bi electrons.Comment: Accepted for publication in Physical Review B. Version 2 includes
additional sample characterisation and bulk measurements, and ab initio
electronic structure calculation
Spin dynamics and exchange interactions in CuO measured by neutron scattering
The magnetic properties of CuO encompass several contemporary themes in
condensed matter physics, including quantum magnetism, magnetic frustration,
magnetically-induced ferroelectricity and orbital currents. Here we report
polarized and unpolarized neutron inelastic scattering measurements which
provide a comprehensive map of the cooperative spin dynamics in the low
temperature antiferromagnetic (AFM) phase of CuO throughout much of the
Brillouin zone. At high energies (\,meV) the spectrum displays
continuum features consistent with the des Cloizeax--Pearson dispersion for an
ideal Heisenberg AFM chain. At lower energies the spectrum
becomes more three-dimensional, and we find that a linear spin-wave model for a
Heisenberg AFM provides a very good description of the data, allowing for an
accurate determination of the relevant exchange constants in an effective spin
Hamiltonian for CuO. In the high temperature helicoidal phase, there are
features in the measured low-energy spectrum that we could not reproduce with a
spin-only model. We discuss how these might be associated with the
magnetically-induced multiferroic behavior observed in this phase
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