Exchange bias and interface electronic structure in Ni/Co3O4(011)

A detailed study of the exchange bias effect and the interfacial electronic structure in Ni/Co3O4(011) is reported. Large exchange anisotropies are observed at low temperatures, and the exchange bias effect persists to temperatures well above the Neel temperature of bulk Co3O4, of about 40 K: to ~80 K for Ni films deposited on well ordered oxide surfaces, and ~150 K for Ni films deposited on rougher Co3O4 surfaces. Photoelectron spectroscopy measurements as a function of Ni thickness show that Co reduction and Ni oxidation occur over an extended interfacial region. We conclude that the exchange bias observed in Ni/Co3O4, and in similar ferromagnetic metallic/Co3O4 systems, is not intrinsic to Co3O4 but rather due to the formation of CoO at the interface.Comment: 8 pages, 6 figures. Accepted for publication in Physical Review B

Interface and electronic characterization of thin epitaxial Co3O4 films

The interface and electronic structure of thin (~20-74 nm) Co3O4(110) epitaxial films grown by oxygen-assisted molecular beam epitaxy on MgAl2O4(110) single crystal substrates have been investigated by means of real and reciprocal space techniques. As-grown film surfaces are found to be relatively disordered and exhibit an oblique low energy electron diffraction (LEED) pattern associated with the O-rich CoO2 bulk termination of the (110) surface. Interface and bulk film structure are found to improve significantly with post-growth annealing at 820 K in air and display sharp rectangular LEED patterns, suggesting a surface stoichiometry of the alternative Co2O2 bulk termination of the (110) surface. Non-contact atomic force microscopy demonstrates the presence of wide terraces separated by atomic steps in the annealed films that are not present in the as-grown structures; the step height of ~ 2.7 A corresponds to two atomic layers and confirms a single termination for the annealed films, consistent with the LEED results. A model of the (1 * 1) surfaces that allows for compensation of the polar surfaces is presented.Comment: 8 pages, 7 figure

État expérimental de la question de l'antiferromagnétisme

Dans son rapport, l'auteur montre, d'une part que les résultats expérimentaux s'interprètent bien en supposant que les interactions négatives entre les ions magnétogènes sont du type indirect de Kramers, qu'elles se font par l'intermédiaire des anions et, d'autre part, que l'étude de l'anisotropie magnétique au-dessous de Tλ permet, dans quelques cas simples, de déterminer la ou les directions d'antiferromagnétisme spontané

Aimantations principales du chlorure et du bromure chromiques

The curves describing as a function of temperature, and for different values of the magnetic field, the principal magnetizations of chromic chloride and bromide show that these compounds are antiferromagnetic below 16.8 and 37.7 °K respectively.Les courbes représentant en fonction de la température, et pour différentes valeurs du champ magnétique, les aimantations principales du chlorure et du bromure chromiques montrent que ces composés sont antiferromagnétiques au-dessous respectivement de 16,8 et 37,7 °K

Susceptibilités magnétiques principales des chlorure, bromure et iodure cobalteux

Below Tλ, the direction of antiferromagnetism is perpendicular to the crystal axis in CoCl2 and CoBr2, and parallel to this axis in CoI2. The susceptibility χ〉 of CoI2 increases as the temperature decreases below T λ.Au-dessous de Tλ, la direction d'antiferromagnétisme est normale à l'axe du cristal dans le cas de CoCl2 et de C OBr2, parallèle à cet axe dans le cas de CoI2. La susceptibilité χ〉 de CoI2 croît lorsque la température s'abaisse au-dessous de Tλ