A High-Resolution Combined Scanning Laser- and Widefield Polarizing Microscope for Imaging at Temperatures from 4 K to 300 K

Polarized light microscopy, as a contrast-enhancing technique for optically anisotropic materials, is a method well suited for the investigation of a wide variety of effects in solid-state physics, as for example birefringence in crystals or the magneto-optical Kerr effect (MOKE). We present a microscopy setup that combines a widefield microscope and a confocal scanning laser microscope with polarization-sensitive detectors. By using a high numerical aperture objective, a spatial resolution of about 240 nm at a wavelength of 405 nm is achieved. The sample is mounted on a $^4$He continuous flow cryostat providing a temperature range between 4 K and 300 K, and electromagnets are used to apply magnetic fields of up to 800 mT with variable in-plane orientation and 20 mT with out-of-plane orientation. Typical applications of the polarizing microscope are the imaging of the in-plane and out-of-plane magnetization via the longitudinal and polar MOKE, imaging of magnetic flux structures in superconductors covered with a magneto-optical indicator film via Faraday effect or imaging of structural features, such as twin-walls in tetragonal SrTiO$_3$. The scanning laser microscope furthermore offers the possibility to gain local information on electric transport properties of a sample by detecting the beam-induced voltage change across a current-biased sample. This combination of magnetic, structural and electric imaging capabilities makes the microscope a viable tool for research in the fields of oxide electronics, spintronics, magnetism and superconductivity.Comment: 14 pages, 11 figures. The following article has been accepted by Review of Scientific Instruments. After it is published, it will be found at http://aip.scitation.org/journal/rs

Magnetic study of the M-type doped barium ferrite nanocrystalline powders

We have studied the static magnetic properties of three different M‐type doped barium ferrite compounds prepared by the glass crystallization method. The zero‐field‐cooled (ZFC) and field‐cooled (FC) processes have been recorded at low field and they all show the typical features of a small particle system. The ZFC curves display a broad peak at a temperature TM, which depends on the distribution of particle volumes in the sample. Isothermal magnetization curves M(H) at several temperatures and saturation magnetization Ms as a function of temperature have been measured for the Co‐Ti sample (BaFe10.4Co0.8Ti0.8O19). The dependence on temperature of the macroscopic magnetic parameters has been analyzed. The distribution of blocking temperatures is studied from the derivative of the remanent‐to‐saturation magnetization ratio with respect to temperature and it is fitted to a lognormal distribution, leading to a mean blocking temperature 〈TB〉=(81±40) K. The distribution of volumes of the magnetic unit is also obtained from this fitting. The dependence on temperature of the coercive field follows a Tk‐law below 35 K. The value of the k exponent is discussed within the scope of two models: (i) the aligned case (k=0.5) and (ii) the random case (k=0.77)

La transmission du droit et l'internet juridique

Le droit est le fruit d une intelligence collective. Il s'agit d'une dynamique qui devient naturellement complexe à observer sur l'internet puisque tous les droits s expriment sur les réseaux. Face à ce flot d'informations, la transmission du droit, des droits, devient un enjeu à considérer. Sans oublier l'informatique juridique, nous chercherons à isoler, sur l'internet, la dynamique derrière les expressions humaines. À cette échelle, globale, c est tout un ensemble qui doit être apprécié, l'internet juridique n'est pas seulement de l informatique juridique, ce n est pas non plus une discipline isolée, mais l élément d un maillage, mêlant toute sorte d informations, d émotions, d usages et de technologies qui, bien qu étant souvent étrangères au droit, doivent être également considérés. En insistant sur le projet JurisPedia, nous verrons cette seule dimension humaine en action en soulignant les problèmes non négociables tenant à la fiabilité des informations juridiques. Mais nous verrons également qu il est possible de canaliser ces expressions et de considérer l intelligence, connective sur l internet, pour parfaire la connaissance des droits du monde, par la médiation nécessaire à toute transmission mais également par la mise en place de structures sémantiques fiables.The law is the consequence of a collective intelligence. This dynamic becomes naturally complex to observe, specially when the worldwide laws are considered or when they are expressed on the networks. In front of this flood of informations, the transmission of the law, the laws, becomes an issue to consider. We don t forget the computer law but we ll try to isolate, on the Internet, the dynamic behind human expressions. On this global level, it s a whole that must be considered. The legal Internet is not only the computer law and it is not an isolated disciplines too. Legal Internet is the element of a mesh, mixing all kinds of information, emotions, customs and technologies which, although often unknown to the law, should also be considered. While insisting on the JurisPedia project, we will see this only human dimension in action by underlining the unnegotiable problems holding with the reliability of the legal information. Then we will see that it s possible to channel these expressions around an instable project and, especially, to consider intelligence, connected on the Internet, to increase the knowledge of the worldwide law, with the mediation needed for any transmissions, but also by the installation of relevants semantics structures.MONTPELLIER-BU Droit (341722102) / SudocSudocFranceF

Erasing the glassy state in magnetic fine particles

BaFe10.4Co0.8Ti0.8O19 magnetic fine particles exhibit most of the features attributed to glassy behavior, e.g., irreversibility in the hysteresis loops and in the zero-field-cooling and field-cooling curves extends up to very high fields, and aging and magnetic training phenomena occur. However, the multivalley energy structure of the glassy state can be strongly modified by a field-cooling process at a moderate field. Slow relaxation experiments demonstrate that the intrinsic energy barriers of the individual particles dominate the behavior of the system at high cooling fields, while the energy states corresponding to collective glassy behavior play the dominant role at low cooling fields

Magnetic Properties of Barium Hexaferrite Powders

In this paper, the magnetic properties of unsubstituted and substituted barium hexaferrite powders are examined. The powders were prepared by the glass crystallization method and characterized geometrically by electron microscopy, and magnetically by measurements of remanence curves. From an analysis of the energy barrier distributions determined from the differential of the primary remanence curves, it is shown that changing the substitution level influences the effective mean anisotropy field of the particles. Consequently this influences the magnetic microstructure as the coupling between the easy axis and the moment of the particle changes. Transverse susceptibility measurements were also made to obtain the values of the anisotropy field which are compared to VSM measurements. © 1994