Volume 89, Issue 11, 01 June 2001
Index of content:
- MAGNETISM AND SUPERCONDUCTIVITY (PACS 74-76)
89(2001); http://dx.doi.org/10.1063/1.1367877View Description Hide Description
In order to clarify the effect of oxygen in the sputtering atmosphere on the microstructure and giant magnetoresistance, Co/Cu multilayers were fabricated under a sputtering atmosphere into which regulated impurity oxygen gas was introduced. After being pumped down the sputtering chamber to the ultimate pressure (less than Torr), oxygen was introduced into the chamber until its content in processing Ar gas was about 0.1 ppm to 0.1%. The magnetoresistance(MR) ratio drastically increased from less than 20% to 54% when the content of impurity oxygen was slightly increased from 20 to 80 ppm, then nearly vanished when the content became more than 200 ppm. In the former region where the MR ratio steeply increased, the root mean square roughness of the multilayers decreased from 6.5 to 4.5 Å accompanied by a reduction in grain size as the oxygen content was increased. The partial oxidation of the multilayers is the most probable mechanism by which the flattening of the interfaces in the multilayer can be explained. We conclude that the impurity oxygen in the sputtering atmosphere serves as an obstruction of grain growth in the multilayer, not as a surfactant for the film growth.
89(2001); http://dx.doi.org/10.1063/1.1368398View Description Hide Description
Nitrogen incorporates into Fe thin films during reactively sputtered TiN capping layer deposition. The influence that this nitrogen incorporation has both on the structure and magnetic properties is discussed for a series of Fe(001) thin filmsgrown at different temperatures. A higher nitrogen content is accompanied by distortion in the Fe lattice and by reduction in the Fe magnetization saturation as well as in the effective anisotropy constant, K. The reduction of K brings as a consequence lowering in the coercive field with respect to equivalent Fe films with no nitrogen present.
89(2001); http://dx.doi.org/10.1063/1.1370369View Description Hide Description
Enhanced low-field magnetoresistance(MR) of polycrystallinelanthanumstrontium manganite thin films is demonstrated using an approach in which effective barriers are formed by the heat-treatment induced reaction with an insulating substrate. The heat treatment induces two chemically different processes in the film, i.e., grain growth and chemically reactive penetration. In the former process, the MR decreases due to reduction of the number of grain boundaries, while in the latter the penetration of an insulating substrate and reacted materials forms effective barriers for the electron tunneling between ferromagnetic grains. The formation of effective barriers causes a factor of 3 larger MR than as-prepared films. These results suggest that the MR can be prospectively controlled in this fashion.
89(2001); http://dx.doi.org/10.1063/1.1369408View Description Hide Description
Magnetitenanorods have been prepared by the sonication of aqueous iron(II)acetate in the presence of β-cyclodextrin. The properties of the magnetitenanorods were characterized by x-ray diffraction, Mössbauer spectroscopy,transmission electron microscopy, thermogravimetric analysis, and magnetization measurements. The as-prepared magnetitenanorods are ferromagnetic and their magnetization at room temperature is The particle sizes measured from transmission electron micrographs are about 48/14 nm (L/W). A mechanism for the sonochemical formation of magnetitenanorods is discussed.
89(2001); http://dx.doi.org/10.1063/1.1345866View Description Hide Description
Granular Co/AlN multilayers, with Co thicknesses varying from 0.2 to 3 nm, were prepared by sputtering. The goal was to prepare Co clusters embedded in a ceramic matrix and to study their magnetic properties. The local surrounding of the Co atoms was characterized via x-ray absorption spectroscopy. The magnetic properties were found to depend markedly on the Co thickness. The findings can be explained in terms of strong chemical interaction between Co and AlN.