Papers by Bernard Barbara
International Journal of Cosmology, Astronomy and Astrophysics
Very simple experiments based on an analogy between two theories gravitation and capillarity allo... 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 (a few hours) 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.
Le Journal de Physique Colloques, 1988
Magnetization and specific heat experiments of usual magnetic and non-magnetic heavy fermions (CeMg,
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
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 of Low Temperature Physics
ABSTRACT
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.
Journal de Physique, 1987
NATO ASI Series, 1990
It is now well established that the static properties of amorphous magnets can be accurately desc... more It is now well established that the static properties of amorphous magnets can be accurately described by the random anisotropy model (1) beyond the mean field approximation (2), in which long range ferromagnetic order is broken under the effect of even weak random anisotropy field fluctuations (see ref.1–6 for theoretical considerations and ref.7–14 for experimental ones). We have recently started the study of the dynamics of these systems at low temperature and near the freezing point (15–21). In this paper we shall give a review on the results concerning low frequencies rotational dynamics (16–20) and moderate frequencies ac susceptibilities at low temperatures (21).
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
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 Physics: Conference Series, 2006
We investigate macroscopic quantum tunneling of magnetization in a a spinor Bose-Einstein condens... more We investigate macroscopic quantum tunneling of magnetization in a a spinor Bose-Einstein condensate trapped in a double-well potential. Using the mean field theory applicable for large condensates, and employing the single spatial mode approximation we derive dynamical equations for magnetization, independent from density mode, for certain initial conditions. We show that they can be reduced to standard Josephson junction dynamics equations under certain conditions.
Journal of Magnetism and Magnetic Materials, 1995
... ld be noted that ties particle size effect involves renses with the amorphous rose, H_ being ... more ... ld be noted that ties particle size effect involves renses with the amorphous rose, H_ being uced by Re. ... experiments and e:-.culat:ons are being performed in order to precise o^ understanding of the magnetic properties of these film; we will for example reduce the particle size. ...
IEEE Transactions on Magnetics, 2010
The magnetic properties of the soft underlayer (SUL) of perpendicular recording media affect the ... more The magnetic properties of the soft underlayer (SUL) of perpendicular recording media affect the recording performance significantly. We visualized and quantified the distribution and magnitude of magnetic flux in the recording layer and SULs of perpendicular recording media by electron holography. Pseudo-SULs with different permeability were deposited on the slider of perpendicular recording heads. The SUL with higher permeability produced higher write magnetic flux () as compared to the SUL with lower permeability, which results higher overwrite performance. Further, the magnitude profile of in the SUL thickness direction was different for the two SULs; the magnitude of magnetic flux in SUL is related to the occurrence of adjacent track erasure.
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
Arxiv preprint arXiv: …, 2010
In a recent letter, it has been predicted within first principle studies that Mn-doped ZrO 2 comp... more In a recent letter, it has been predicted within first principle studies that Mn-doped ZrO 2 compounds could be good candidate for spintronics application because expected to exhibit ferromagnetism far beyond room temperature. Our purpose is to address this issue experimentally for Mn-doped tetragonal zirconia. We have prepared polycrystalline samples of Y 0.15 (Zr 0.85-y Mn y)O 2 (y=0, 0.05, 0.10, 0.15 & 0.20) by using standard solid state method at equilibrium. The obtained samples were carefully characterized by using x-ray diffraction, scanning electron microscopy, elemental color mapping, X-ray photoemission spectroscopy and magnetization measurements. From the detailed structural analyses, we have observed that the 5% Mn doped compound crystallized into two symmetries (dominating tetragonal & monoclinic), whereas higher Mn doped compounds are found to be in the tetragonal symmetry only. The spectral splitting of the Mn 3s core-level x-ray photoelectron spectra confirms that Mn
Applied Physics Letters, 2005
A detailed study of exchange-biased Fe∕MnF2 bilayers using magneto-optical Kerr effect shows that... more A detailed study of exchange-biased Fe∕MnF2 bilayers using magneto-optical Kerr effect shows that the magnetization reversal occurs almost fully through domain wall nucleation and propagation for external fields parallel to the exchange-bias direction. For finite angles ϕ between bias and external field, the magnetization is aligned perpendicular to the cooling-field direction for a limited field range for decreasing fields. For external fields perpendicular to the bias direction, the magnetization aligns with the cooling-field direction for descending and ascending fields before fully reversing. The field range for which the magnetization is close to perpendicular to the external field can be estimated using a simple effective-field model.
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Papers by Bernard Barbara