Papers by Bernard Barbara
arXiv (Cornell University), Apr 23, 2022
Very simple experiments based on an analogy between two theories __ gravitation and capillarity _... more Very simple experiments based on an analogy between two theories __ gravitation and capillarity __ allowed us to construct a 2-dimensional-space toy-universe (U2D) composed of the surface of a 3D water tank with floating soap bubbles and bubble clusters. The experiments performed with or without a "black hole" suggest that our visible universe (U3D) is composed of the 3D "surface" of a 4D universe essentially filled with a heavy fluid that, interestingly, possesses all the properties presently attributed to "dark matter". The observations of this U2D and their implications for the structure and evolution of our U3D are discussed openly without preconceptions, not to say naively. This analogy led us to propose a scenario reproducing several observations made in our U3D. It would also allow us to schematically investigate the evolution of portions of our visible universe (stars, black holes, galaxies) at easily available timescales (seconds, to days) in contrast with the billions of years required for direct observations. More basically, it suggests that the 4D volume of our universe, which is inaccessible to us, constitutes a huge tank of heavy fluid sitting "below" our 3D surface universe and this has several consequences such as an original interpretation of the event horizon of black holes or a simple answer to the problem of missing dark matter. 1-Introduction Starting from an analogy between capillarity and gravitation we experimentally created __ approximately 15 years ago __ a model for a two-dimensional universe (U2D) and compared it to our own three-dimensional universe (U3D). This model simply consists of the observation of different static or dynamical configurations of soap bubbles floating on the surface of a tank filled with a liquid (water) which, through the capillary forces analogous to the Newton's gravitational forces, gather in aggregates that represent the massive objects of our U3D, such as planets and stars. After some improvements we also created a U2D black hole. The water menisci that form around each floating object __ from
Le Journal de Physique Colloques, 1988
Magnetization and specific heat experiments of usual magnetic and non-magnetic heavy fermions (CeMg,
Solid State Communications, 1985
Magnetization measurements have been performed on a single crystal of CeCu6 along the three main ... more Magnetization measurements have been performed on a single crystal of CeCu6 along the three main crystallographic directions between 1.5 and 300 K. The results are interpreted in terms of a crystal field calculation slightly modified by a spin fluctuation contribution of Kondo origin. Anisotropic magnetic properties of the Kondo lattice are discussed.
Journal de Physique, 1987
Journal of Physics F: Metal Physics, 1987
ABSTRACT Accurate measurements of the electrical resistivity ( rho ) and its temperature derivati... more ABSTRACT Accurate measurements of the electrical resistivity ( rho ) and its temperature derivative (d rho /dT) have been performed in a set of random anisotropy alloys a-DyxGd1-xNi (x=0.1, 0.25, 0.5, 0.75 and 1.0) exhibiting magnetic freezing at temperatures (Tf) ranging from approximately 60 K to approximately 14 K, and a negative d rho /dT in the paramagnetic phase. For the Gd-rich samples, which have a low anisotropy energy D (D/J approximately 10-2; J=exchange energy), the magnetic resistivity ( rho m) increases steadily with temperature until saturation above Tf; in contrast, for the Dy-rich samples (large anisotropy, D approximately J) rho m decreases with increasing temperature near Tf. These results are interpreted qualitatively in terms of a schematic model based on the existence of effective antiferromagnetic pairs located at the boundary of Imry and Ma domains (1975). This interpretation is supported by magnetoresistance measurement performed in the authors' samples. They also analyse the x dependence of rho m along the series at constant reduced temperatures. An approximately linear dependence of rho m on x was found both above and below Tf (at least down to T/Tf approximately=0.5, for all the samples except x=0.1). Their d rho /dT results exhibit pronounced anomalies near Tf, which enable the accurate determination of Tf in the samples investigated. Accurate measurements of the electrical resistivity ( rho ) and its temperature derivative (d rho /dT) have been performed in a set of random anisotropy alloys a-DyxGd1-xNi (x=0.1, 0.25, 0.5, 0.75 and 1.0) exhibiting magnetic freezing at temperatures (Tf) ranging from approximately 60 K to approximately 14 K, and a negative d rho /dT in the paramagnetic phase. For the Gd-rich samples, which have a low anisotropy energy D (D/J approximately 10-2; J=exchange energy), the magnetic resistivity ( rho m) increases steadily with temperature until saturation above Tf; in contrast, for the Dy-rich samples (large anisotropy, D approximately J) rho m decreases with increasing temperature near Tf. These results are interpreted qualitatively in terms of a schematic model based on the existence of effective antiferromagnetic pairs located at the boundary of Imry and Ma domains (1975). This interpretation is supported by magnetoresistance measurement performed in the authors' samples. They also analyse the x dependence of rho m along the series at constant reduced temperatures. An approximately linear dependence of rho m on x was found both above and below Tf (at least down to T/Tf approximately=0.5, for all the samples except x=0.1). Their d rho /dT results exhibit pronounced anomalies near Tf, which enable the accurate determination of Tf in the samples investigated.
This paper deals with the broad class of magnetic systems having a single or collective spin S wi... more This paper deals with the broad class of magnetic systems having a single or collective spin S with an energy barrier, such as Rare-Earth elements and their compounds, Single Molecule Magnets with uniaxial anisotropy and more generally any other anisotropic quantum system made of single or multiple objects with discrete energy levels. Till now, the reversal of the magnetization of such systems at zero Kelvin required to make use of quantum tunneling with a significant transverse field or transverse anisotropy term, at resonance. Here, we show that another very simple method exists. It simply consists in the application of a particular sequence of electromagnetic radiations in the ranges of optical or microwave frequencies, depending on the characteristics of the system (spin and anisotropy values for magnetic systems). This produces oscillations of the Rabi type that pass above the barrier, thus extending these oscillations between the two energy wells with mixtures of all the 2S + 1 states. In addition to its basic character, this approach opens up new directions of research in quantum information with possible breakthroughs in the current use of multiple quantum bits.
Physical Review Letters, 1980
Neutron diffraction experiments under perturbations, such as uniaxial stress and hydrostatic pres... more Neutron diffraction experiments under perturbations, such as uniaxial stress and hydrostatic pressure, suggest strongly that CeA1& exhibits bvo magnetic phases: a single-q collinear modulated structure and a type-II antiferromagnetic structure.
Solid State Communications, 1985
Values for the random anisotropy (D) and exchange (J) constants in amorphous DyxGd 1-xNi have bee... more Values for the random anisotropy (D) and exchange (J) constants in amorphous DyxGd 1-xNi have been obtained from an analysis of the measured magnetization curves in terms of the H.P.Z. model. Within the molecular field approximation this model is suitable in high magnetic fields In low fields, other properties, characteristic of random anisotropy systems, arise which are not taken into account in this model.
Solid State Communications, 1977
Physics of the Solid State, 2001
ABSTRACT The process of rearrangement of the magnetic structure of the low-spin cluster V15 in su... more ABSTRACT The process of rearrangement of the magnetic structure of the low-spin cluster V15 in superhigh magnetic fields is investigated. At low temperatures, this process is shown to manifest itself as three quantum jumps, each of which is a transition causing the spin of the complex to increase by two unities. The nature of these quantum jumps is discussed. The magnetization curve and the magnetic susceptibility are calculated.
Physica C: Superconductivity, 1988
The thermal conductivity of YBa2Cu307-& has been measured between 0.1 and 7 K. The data are simil... more The thermal conductivity of YBa2Cu307-& has been measured between 0.1 and 7 K. The data are similar in magnitude and temperature dependence to data for other sintered ceramics.
Physica B: Condensed Matter, 1994
The magnetic susceptibility chi(H, T) of the paramagnetic Y0.5Ni0.5 amorphous alloy was measured ... more The magnetic susceptibility chi(H, T) of the paramagnetic Y0.5Ni0.5 amorphous alloy was measured with a SQUID at low fields (H<500Oe) and in the temperature range 1.3<T<25K. Besides a small field independent Curie-like contribution C/T due to about 100 ppm of magnetic rare-earth impurities in Y, we find that chi(H, T) presents a &surd;T dependence: chi(H, T)=C/T+chio(H)-A(H)&surd;T, A(H) being a linear function of chio(H). The results are analyzed in terms of the quantum corrections to the magnetic susceptibility in the weak localization regime in 3-dimensional systems.
Journal of Physics: Condensed Matter, 1992
The authors report on the magnetic relaxation of thin films of Fe of 1000 AA thickness separated ... more The authors report on the magnetic relaxation of thin films of Fe of 1000 AA thickness separated by layers of Ag of 15 AA thickness. It is argued that the flattening of the magnetic viscosity at low temperature may be due to quantum diffusion of domain walls. Both the crossover temperature, Tc, from the classical to the quantum regime and the magnetic viscosity extrapolated to T=0 depend on the value of the applied field, in agreement with theories of quantum tunnelling in magnets.
Journal of Magnetism and Magnetic Materials, 1997
The passage of a 180° domain wall (DW) from a 1000 Å thick uniaxial GdFe amorphous layer to a 500... more The passage of a 180° domain wall (DW) from a 1000 Å thick uniaxial GdFe amorphous layer to a 500 Å layer through a thin TbFe layer is presented. In this system, the TbFe layer acts as a potential energy barrier for the DW. The propagation field Hp at which the DW crosses the barrier is shown to increase linearly
Journal of Magnetism and Magnetic Materials, 1997
GdFe amorphous layers have been prepared with well defined in-plane magnetic anisotropy. The best... more GdFe amorphous layers have been prepared with well defined in-plane magnetic anisotropy. The best results were obtained when the sample was deposited on glass substrate kept at 90 K during the deposition process. When the substrate was kept at room temperature the anisotropy is less well defined and a perpendicular anisotropy component appears as the thickness of the layer increases.
Bulletin of the American …, 2011
The onset of correlation effects in the magnetic Ho$^{3+}$-subsystem in LiHo$_{x}$Y$_{1-x}$ F$_{4... more The onset of correlation effects in the magnetic Ho$^{3+}$-subsystem in LiHo$_{x}$Y$_{1-x}$ F$_{4}$ single crystals is studied by comparing measurements and simulations of the field and frequency dependent magnetic AC susceptibility at 1.8 K and field and temperature ...
Europhysics Letters (EPL), 1993
A GdFe (100 nm) / TbFe (e) / GdFe (50 nm) trilayer, where the thickness e of the TbFe layer can b... more A GdFe (100 nm) / TbFe (e) / GdFe (50 nm) trilayer, where the thickness e of the TbFe layer can be as thin as 0.2 nm, constitutes a domain wall junction. In this device, a 180=B0 domain wall nucleated in the thicker GdFe layer crosses the artificial potential energy barrier due to TbFe layer by thermal activation for temperatures higher than 1K. Below this temperature, anomalous behaviours are observed in the dynamical measurements of the crossing of the barrier. Quantum tunnelling of magnetisation is suggested.
Philosophical Magazine B, 2000
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Papers by Bernard Barbara