304 research outputs found
SQUID measurements of remanent magnetisation in refillable 3He spin filter cells SFC
A strong influence of external magnetic fields on the relaxation time constant T1 of glass cells serving as 3He neutron spin filters, observed for different glass types in alkali metal coated cells, was initially associated with the presence of a large number of ferromagnetic clusters on the glass surface. Later experiments showed the presence of the so called T1 hysteresis phenomenon with a similar distinctiveness also in uncoated cells made of pure synthetic quartz glass. It suggests that the origin of such relaxation is a macroscopic magnetisation in the bulk material of the cell. We present the results of a multi SQUID system investigation on magnetised and non magnetised quartz glass cells, Cs coated as well as bare wall, to be used as neutron spin filters at HMI Berlin. The presence of a macroscopic remanent magnetic moment in the cells after their exposition to external magnetic fields has been experimentally shown. More than 80 of the remanent magnetic moment of the magnetised cells was found to be concentrated in the region around the glass valves. SQUID measurements reveal the existence of some remanent magnetisation in all valve parts and also in the vacuum grease, but most magnetic are the plastic parts and the O ring. Different valve and sealing types has been compared in order to find less magnetisable on
Low temperature magnetic structure of CeRhIn by neutron diffraction on absorption-optimized samples
Two aspects of the ambient pressure magnetic structure of heavy fermion
material CeRhIn have remained under some debate since its discovery:
whether the structure is indeed an incommensurate helix or a spin density wave,
and what is the precise magnitude of the ordered magnetic moment. By using a
single crystal sample optimized for hot neutrons to minimize neutron absorption
by Rh and In, here we report an ordered moment of . In
addition, by using spherical neutron polarimetry measurements on a similar
single crystal sample, we have confirmed the helical nature of the magnetic
structure, and identified a single chiral domain
Neutron inelastic scattering study of rare-earth orthoferrite HoFeO
By the single crystal inelastic neutron scattering the orthoferrite HoFeO3
was studied. We show that the spin dynamics of the Fe subsystem does not change
through the spin-reorientation transitions. The observed spectrum of magnetic
excitations was analyzed in the frames of linear spin-wave theory. Within this
approach the antiferromagnetic exchange interactions of nearest neighbors and
next nearest neighbors were obtained for Fe subsystem. Parameters of
Dzyaloshinskii-Moriya interactions at Fe subsystem were refined. The
temperature dependence of the gap in Fe spin-wave spectrum indicates the
temperature evolution of the anisotropy parameters. The estimations for the
values of Fe-Ho and Ho-Ho exchange interaction were made as well
Homo-chiral crystal growth and mono-chiral helimagnetism in inorganic chiral magnetic compounds
Trabajo presentado al International Workshop on Multipole Physics and Related Phenomena (J-Physics), celebrado en Hachimantai, Iwate (Japón) del 24 al 28 de septiembThis work was supported by JSPS KAKENHI Grant Number 25220803, 25390139, 26108719, 15H03680, 15H05885, 15H05886, 16KK0102, 17H02912, 17H02767, and 17H02815. JC acknowledges the Grant Number MAT2015-68200-C2-2-P from the Spanish Ministry of Economy and Competitiveness.Peer Reviewe
Tunable Emergent Heterostructures in a Prototypical Correlated Metal
At the interface between two distinct materials desirable properties, such as
superconductivity, can be greatly enhanced, or entirely new functionalities may
emerge. Similar to in artificially engineered heterostructures, clean
functional interfaces alternatively exist in electronically textured bulk
materials. Electronic textures emerge spontaneously due to competing
atomic-scale interactions, the control of which, would enable a top-down
approach for designing tunable intrinsic heterostructures. This is particularly
attractive for correlated electron materials, where spontaneous
heterostructures strongly affect the interplay between charge and spin degrees
of freedom. Here we report high-resolution neutron spectroscopy on the
prototypical strongly-correlated metal CeRhIn5, revealing competition between
magnetic frustration and easy-axis anisotropy -- a well-established mechanism
for generating spontaneous superstructures. Because the observed easy-axis
anisotropy is field-induced and anomalously large, it can be controlled
efficiently with small magnetic fields. The resulting field-controlled magnetic
superstructure is closely tied to the formation of superconducting and
electronic nematic textures in CeRhIn5, suggesting that in-situ tunable
heterostructures can be realized in correlated electron materials
Physics beyond the standard model with kaons at NA62
The NA62 experiment at CERN Super Proton Synchrotron was designed to measure BR(K+ \u2192 \u3c0+\u3bdv\u304) with an in-fight technique, never used before for this measurement. This decay is characterised by a very precise prediction in the Standard Model. Its branching ratio, which is expected to be less than 10-10, is one of the best candidates to indicate indirect effects of new physics beyond SM at the highest mass scales. NA62 result on K+ \u2192 \u3c0+\u3bdv\u304 from the full 2016 data set is described. Also a search for an invisible dark photon A\u2032 has been performed, exploiting the efficient photon-veto capability and high resolution tracking of the NA62. The signal stems from the chain K+ \u2192 \u3c0+\u3c00 followed by \u3c00 \u2192 A\u2032\u3b3. No significant statistical excess has been identified. Upper limits on the dark photon coupling to the ordinary photon as a function of the dark photon mass have been set, improving on the previous limits over the mass range 60 - 110 MeV/c2
Externalities and the nucleolus
In most economic applications, externalities prevail: the worth of a coalition depends on how the other players are organized. We show that there is a unique natural way of extending the nucleolus from (coalitional) games without externalities to games with externalities. This is in contrast to the Shapley value and the core for which many different extensions have been proposed
Search for π⁰ decays to invisible particles
The NA62 experiment at the CERN SPS reports a study of a sample of 4 × 109 tagged π0 mesons from K+ → π+π0(γ), searching for the decay of the π0 to invisible particles. No signal is observed in excess of the expected background fluctuations. An upper limit of 4.4 × 10−9 is set on the branching ratio at 90% confidence level, improving on previous results by a factor of 60. This result can also be interpreted as a model- independent upper limit on the branching ratio for the decay K+ → π+X, where X is a particle escaping detection with mass in the range 0.110–0.155 GeV/c2 and rest lifetime greater than 100 ps. Model-dependent upper limits are obtained assuming X to be an axion-like particle with dominant fermion couplings or a dark scalar mixing with the Standard Model Higgs boson
Searches for lepton number violating K+ decays
The NA62 experiment at CERN reports a search for the lepton number violating decays K+→π−e+e+ and K+→π−μ+μ+ using a data sample collected in 2017. No signals are observed, and upper limits on the branching fractions of these decays of 2.2 x 10^-10 and 4.2 x 10^-11 are obtained, respectively, at 90% confidence level. These upper limits improve on previously reported measurements by factors of 3 and 2, respectively
- …