Anisotropic susceptibility of ferromagnetic ultrathin Co films on vicinal Cu

We measure the magnetic susceptibility of ultrathin Co films with an in-plane uniaxial magnetic anisotropy grown on a vicinal Cu substrate. Above the Curie temperature the influence of the magnetic anisotropy can be investigated by means of the parallel and transverse susceptibilities along the easy and hard axes. By comparison with a theoretical analysis of the susceptibilities we determine the isotropic exchange interaction and the magnetic anisotropy. These calculations are performed in the framework of a Heisenberg model by means of a many-body Green's function method, since collective magnetic excitations are very important in two-dimensional magnets.Comment: 7 pages, 3 figure

Survey Sequencing and Comparative Analysis of the Elephant Shark (Callorhinchus milii) Genome

Owing to their phylogenetic position, cartilaginous fishes (sharks, rays, skates, and chimaeras) provide a critical reference for our understanding of vertebrate genome evolution. The relatively small genome of the elephant shark, Callorhinchus milii, a chimaera, makes it an attractive model cartilaginous fish genome for whole-genome sequencing and comparative analysis. Here, the authors describe survey sequencing (1.4× coverage) and comparative analysis of the elephant shark genome, one of the first cartilaginous fish genomes to be sequenced to this depth. Repetitive sequences, represented mainly by a novel family of short interspersed element–like and long interspersed element–like sequences, account for about 28% of the elephant shark genome. Fragments of approximately 15,000 elephant shark genes reveal specific examples of genes that have been lost differentially during the evolution of tetrapod and teleost fish lineages. Interestingly, the degree of conserved synteny and conserved sequences between the human and elephant shark genomes are higher than that between human and teleost fish genomes. Elephant shark contains putative four Hox clusters indicating that, unlike teleost fish genomes, the elephant shark genome has not experienced an additional whole-genome duplication. These findings underscore the importance of the elephant shark as a critical reference vertebrate genome for comparative analysis of the human and other vertebrate genomes. This study also demonstrates that a survey-sequencing approach can be applied productively for comparative analysis of distantly related vertebrate genomes

TRANSITION DU PREMIER ORDRE DANS LES CRISTAUX CUBIQUES INDUITE PAR UN CHAMP MAGNÉTIQUE ORIENTÉ SUIVANT UNE DIRECTION DE DIFFICILE AIMANTATION

Dans les cristaux cubiques, un champ magnétique dirigé suivant un axe de difficile aimantation, peut induire une transition de premier ordre. En utilisant le développement classique de l'énergie magnétocristalline, on a déterminé les relations existant entre les constantes d'anisotropie pour qu'une telle transition apparaisse. On donne pour exemple le fer et le nickel à 4,2 °K.In cubic crystals, a magnetic field applied along a hard direction can induce a first order transition. Using classical expansion of magnetocrystalline energy, we have determined the relations between anisotropy constants necessary for such a transition to appear. Iron and nickel at 4.2 °K are given as examples