Tunneling Anisotropic Magnetoresistance in Co/AlOx/Au Tunnel Junctions

We observe spin-valve-like effects in nano-scaled thermally evaporated Co/AlOx/Au tunnel junctions. The tunneling magnetoresistance is anisotropic and depends on the relative orientation of the magnetization direction of the Co electrode with respect to the current direction. We attribute this effect to a two-step magnetization reversal and an anisotropic density of states resulting from spin-orbit interaction. The results of this study points to future applications of novel spintronics devices involving only one ferromagnetic layer.Comment: 11 pages, 5 figures. Accpted for publishing on Nano Letters, 200

Spectroscopic characterization (Raman and infrared) of Aloe maculata from the north Argentina region

9 pags., 9 figs.In this work we present the Fourier-transform infrared (FTIR) and Raman spectra of Aloe maculata (A.maculata)(“maculata” = with spots) gel after elimination of the aloin fraction. The analyzed samples were harvested from two zones of different heights in northern Argentina. From the FTIR measurements it was possible to identify the presence of pectin in the gel, where an analysis of the degree of esterification was done on the basis of characteristic marker bands for the different aloe samples. The effect of the storage time of both samples was also monitored revealing that the degree of esterification undergoes a decrease upon the storage time in all samples. By this way, it was determined that the samples of A. maculata collected from the high lands, present a higher esterification degree in pectins than those collected from the low lands. In order to better follow the distribution of the different spectral signals, we performed a Raman mapping in a selected area. The Raman measurements helped to determine the characteristics of the different fibers of the Aloe gel. Furthermore, theoretical calculations carried out on a molecular model of one important aloe gel component, the acemannan, aided in the assignment of the modes of the groups present in the gel samples. This investigation is important in order to assess the influence of the harvesting place and the storage time on the use and commercialization of the aloe products, since a higher degree of esterification gives rise to a higher viscosity and, consequently, a better bioavailability.We thank PIUNT (D620/3), CONICET (PIP 002 and 1529) of R. Argentina for the research grants. This work has also been supported by the Spanish Ministerio de Ciencia e Innovación and the European Union FEDER funds under PID2020-113900RB-I00/AEI/10.13039/501100011033 project

Direct observation of field and temperature induced domain replication in dipolar coupled perpendicular anisotropy films

International audienceDipolar interactions in a soft/Pd/hard ͓CoNi/ Pd͔ 30 / Pd/ ͓Co/ Pd͔ 20 multilayer system, where a thick Pd layer between two ferromagnetic units prevents direct exchange coupling, are directly revealed by combining mag-netometry and state-of-the-art layer resolving soft x-ray imaging techniques with sub-100-nm spatial resolution. The domains forming in the soft layer during external magnetic field reversal are found to match the domains previously trapped in the hard layer. The low Curie temperature of the soft layer allows varying its intrinsic parameters via temperature and thus studying the competition with dipolar fields due to the domains in the hard layer. Micromagnetic simulations elucidate the role of ͓CoNi/Pd͔ magnetization, exchange, and anisotropy in the duplication process. Finally, thermally driven domain replication in remanence during temperature cycling is demonstrated

Magnetization reversal of ferromagnetic nanowires studied by magnetic force microscopy

The magnetization reversal of two-dimensional arrays of parallel ferromagnetic Fe nanowires embedded in nanoporous alumina templates has been studied. By combining bulk magnetization measurements (superconducting quantum interference device magnetometry) with field-dependent magnetic force microscopy (MFM), we have been able to decompose the macroscopic hysteresis loop in terms of the irreversible magnetic responses of individual nanowires. The latter are found to behave as monodomain ferromagnetic needles, with hysteresis loops displaced (asymmetric) as a consequence of the strong dipolar interactions between them. The application of field-dependent MFM provides a microscopic method to obtain the hysteresis curve of the array, by simply registering the fraction of up and down magnetized wires as a function of applied field. The observed deviations from the rectangular shape of the macroscopic hysteresis loop of the array can be ascribed to the spatial variation of the dipolar field through the inhomogeneously filled membrane. The system studied proves to be an excellent example of the two-dimensional classical Preisach model, well known from the field of hysteresis modeling and micromagnetism.This work was part of the research program of the Stichting voor Fundamenteel Onderzoek der Materie (FOM), which is supported by the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NOW). C.U. and F.L. acknowledge grants funded by the European Union in the framework of its TMR Marie Curie Program. M.K. acknowledges a grant funded by Deutsche Forschungsgemeinschaft (DFG)