3,966 research outputs found
Anomalous quartic WWgamma gamma, ZZgamma gamma, and trilinear WWgamma couplings in two-photon processes at high luminosity at the LHC
We study the W/Z pair production via two-photon exchange at the LHC and give
the sensitivities on trilinear and quartic gauge anomalous couplings between
photons and W/Z bosons for an integrated luminosity of 30 and 200 fb^{-1}. For
simplicity and to obtain lower backgrounds, only the leptonic decays of the
electroweak bosons are considered.Comment: 22 pages, 17 figures, sumitted to Phys. Rev.
Anisotropic interactions opposing magnetocrystalline anisotropy in SrNiIrO
We report our investigation of the electronic and magnetic excitations of
SrNiIrO by resonant inelastic x-ray scattering at the Ir L edge.
The intra- electronic transitions are analyzed using an atomic model,
including spin-orbit coupling and trigonal distortion of the IrO
octahedron, confronted to {\it ab initio} quantum chemistry calculations. The
Ir spin-orbital entanglement is quantified and its implication on the magnetic
properties, in particular in inducing highly anisotropic magnetic interactions,
is highlighted. These are included in the spin-wave model proposed to account
for the dispersionless magnetic excitation that we observe at 90 meV. By
counterbalancing the strong Ni easy-plane anisotropy that manifests
itself at high temperature, the anisotropy of the interactions finally leads to
the remarkable easy-axis magnetism reported in this material at low
temperature
Magnetic order in the frustrated Ising-like chain compound SrNiIrO
We have studied the field and temperature dependence of the magnetization of
single crystals of Sr3NiIrO6. These measurements evidence the presence of an
easy axis of anisotropy and two anomalies in the magnetic susceptibility.
Neutron powder diffraction realized on a polycrystalline sample reveals the
emergence of magnetic reflections below 75 K with magnetic propagation vector k
~ (0, 0, 1), undetected in previous neutron studies [T.N. Nguyen and H.-C zur
Loye, J. Solid State Chem., 117, 300 (1995)]. The nature of the magnetic ground
state, and the presence of two anomalies common to this family of material, are
discussed on the basis of the results obtained by neutron diffraction,
magnetization measurements, and symmetry arguments
Magneto and ferroelectric phase transitions in HoMn2O5 monocrystals
From the physical point of view multiferroics present an extremely
interesting class of systems and problems. These are essentially of two kinds.
One is what are the microscopic conditions, and sometimes constrains, which
determine the possibility to combine in one system both magnetic and
ferroelectric properties. This turned out to be a quite nontrivial question,
and usually, in conventional systems, these two phenomena tend to exclude one
another. Why it is the case is an important and still not completely resolved
issue. In the present article we report our results from magnetic properties
measurements on HoMn2O5 with short discussion about it possible origin
Electric field control of the magnetic chiralities in ferroaxial multiferroic RbFe(MoO4)2
The coupling of magnetic chiralities to the ferroelectric polarisation in
multiferroic RbFe(MoO) is investigated by neutron spherical
polarimetry. Because of the axiality of the crystal structure below
= 190 K, helicity and triangular chirality are
symmetric-exchange coupled, explaining the onset of the ferroelectricity in
this proper-screw magnetic structure - a mechanism that can be generalised to
other systems with "ferroaxial" distortions in the crystal structure. With an
applied electric field we demonstrate control of the chiralities in both
structural domains simultaneously.Comment: 5 pages, 4 figure
Gallium Substituted "114" YBaFe4O7: From a ferrimagnetic cluster glass to a cationic disordered spin glass
The study of the ferrites YBaFe4-xGaxO7 shows that the substitution of Ga for
Fe in YBaFe4O7 stabilizes the hexagonal symmetry for 0.40 < x < 0.70, at the
expense of the cubic one. Using combined measurements of a. c. and d. c.
magnetization, we establish that Ga substitution for Fe in YBaFe4O7 leads to an
evolution from a geometrically frustrated spin glass (for x = 0) to a cationic
disorder induced spin glass (x = 0.70). We also find an intermediate narrow
range of doping where the samples are clearly phase separated having small
ferrimagnetic clusters embedded in a spin glass matrix. The origin of the
ferrimagnetic clusters lies in the change in symmetry of the samples from cubic
to hexagonal (and a consequent lifting of the geometrical frustration) as a
result of Ga doping. We also show the presence of exchange bias and domain wall
pinning in these samples. The cause of both these effects can be traced back to
the inherent phase separation present in the samples.Comment: 25 pages, 10 figure
Quantitative MR renography using a calibrated internal signal (ERETIC)
To measure MR renograms, cortical and medullary kidney signal intensity evolution is followed after contrast agent injection. To obtain an accurate quantitative signal measurement, the use of a reference signal is necessary to correct the potential MRI system variations in time. The ERETIC method (Electronic Reference To access In vivo Concentrations) provides an electronic reference signal. It is synthesized as an amplitude modulated RF pulse applied during the acquisition. The ERETIC method was as precise as the external tube reference method but presents major advantages like its free adjustability (shape, location and magnitude) to the characteristics of the organ studied as well as its not taking room inside the magnet. Even though ERETIC showed a very good intrinsic stability, systems’ variations still affect its signal in the same way as real NMR signals are affected. This method can be easily implemented on any imaging system with two RF channels
Geometric and disorder -- type magnetic frustration in ferrimagnetic "114" Ferrites: Role of diamagnetic Li+ and Zn2+ cation substitution
The comparative study of the substitution of zinc and lithium for iron in the
"114" ferrites, YBaFe4O7 and CaBaFe4O7, shows that these diamagnetic cations
play a major role in tuning the competition between ferrimagnetism and magnetic
frustration in these oxides. The substitution of Li or Zn for Fe in the cubic
phase YBaFe4O7 leads to a structural transition to a hexagonal phase
YBaFe4-xMxO7, for M = Li (0.30 < x < 0.75) and for M = Zn (0.40 < x < 1.50). It
is seen that for low doping values i.e. x = 0.30 (for Li) and x = 0.40 (for
Zn), these diamagnetic cations induce a strong ferrimagnetic component in the
samples, in contrast to the spin glass behaviour of the cubic phase. In all the
hexagonal phases, YBaFe4-xMxO7 and CaBaFe4-xMxO7 with M = Li and Zn, it is seen
that in the low doping regime (x ~ 0.3 to 0.5), the competition between
ferrimagnetism and 2 D magnetic frustration is dominated by the average valency
of iron. In contrast, in the high doping regime (x ~ 1.5), the emergence of a
spin glass is controlled by the high degree of cationic disorder, irrespective
of the iron valency.Comment: 2 tables, 7 figure
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